Routine Turtle and Dugong Monitoring Program Report Dredging Report 2

Transcription

1 Routine Turtle and Dugong Monitoring Program Report Dredging Report 2 Ichthys Nearshore Environmental Monitoring Program L384-AW-REP Prepared for INPEX July 2013

2 Document Information Prepared for Project Name File Reference Job Reference INPEX Date July 2013 L384_AW_REP_10246_0_Routine Turtle and Dugong Monitoring Program Report Dredging Report 2.docm L384-AW-REP Contact Information Cardno (NSW/ACT) Pty Ltd Cardno (WA) Pty Ltd Cardno (NT) Pty Ltd Level 9, The Forum 11 Harvest Terrace Level 6, 93 Mitchell Street 203 Pacific Highway West Perth WA 6005 Darwin NT 0800 St Leonards NSW 2065 Telephone: Telephone: Telephone: Facsimile: Facsimile: Facsimile: International: International: International: Document Control Version Date Author Author Initials Reviewer Reviewer Initials A 14/06/2013 Michelle Blewitt MLB Craig Blount CB Megan Rice MR Joanna Lamb JL B 28/06/2013 Megan Rice MR Craig Blount CB Lachlan Barnes LB Joanna Lamb JL C 18/07/2013 Michelle Blewitt MLB Craig Blount Joanna Lamb D 24/7/2013 Michelle Blewitt MLB Craig Blount Joanna Lamb CB JL CB JL 0 25/07/2013 Michelle Blewitt MLB Joanna Lamb JL This document is produced by Cardno solely for the benefit and use by the client in accordance with the terms of the engagement for the performance of the Services. Cardno does not and shall not assume any responsibility or liability whatsoever to any third party arising out of any use or reliance by any third party on the content of this document. Prepared for INPEX Cardno ii

3 Executive Summary A Turtle and Dugong Monitoring Program (TDMP) has been developed to monitor variability of turtle and dugong relative abundance and distribution in Darwin Harbour/Hope Inlet and surrounding areas during dredging and spoil disposal activities associated with the Ichthys Project in Darwin Harbour. The TDMP incorporates various visual survey techniques to estimate and monitor turtle and dugong populations within these areas. The key objectives of the TDMP are to: > Quantify the variability of turtle and dugong relative abundance and distribution in the inshore waters of Darwin Harbour and nearshore waters between and within surveys. Observe changes in these parameters over the duration of the dredging and post dredging periods; and > Assess fine-scale aspects of dugong and turtle populations within Darwin Harbour in relation to potential habitat use and identify foraging areas (if possible). This report outlines the findings of the second Dredging Phase survey undertaken between 9 May 2013 and 27 May 2013 (D2), approximately six months after the commencement of Cutter Suction Dredger (CSD) operations. Data collected via standardised aerial transects undertaken during the current survey has enabled a comparison of turtle and dugong sightings, population estimates and density at three locations - Bynoe Harbour (Control Location 1 - C1), Darwin Harbour/Hope Inlet region (Impact location - IM), and the Vernon Islands and Melville Island (Control Location 2 - C2) - with data collected prior to the initiation of CSD activities (Baseline Phase). The addition of land observations during the Dredging Phase has provided an opportunity to examine the use of alternate observational methods to identify finer-scale turtle and dugong habitat associations within Darwin Harbour. It should be noted that the third Baseline Phase survey (B3) completed in September 2012 and October 2012 was undertaken after the commencement of the Backhoe Dredger (BHD) operations, but prior to the start of CSD operations. During B3, sediment plumes from BHD operations were observed to be minimal and localised to a very small area and, as such, the first Dredging Phase survey was considered part of the Baseline Phase (i.e. B3) and has been reported previously as D1. The current survey is considered the first during dredging survey; however, to avoid confusion with B3 (D1), this survey has been recorded as D2. Aerial Surveys Aerial surveys collect data at a large spatial scale to meet the first objective of the TDMP. During D2, 1,358.5 km of linear transect was flown equating to a survey area of km 2 over approximately 38 hour flying period. The overall monitoring area (i.e. area within the transect boundaries) during D2 equated to 2,974 km 2 across all three geographical survey locations. Approximately 18% of the available area within each location was surveyed during D2. Dugongs Fewer dugongs were sighted within each location surveyed during D2 (33 individuals) compared to the average observed throughout the Baseline Phase (88 individuals). The mean numbers of dugongs sighted per replicate flight during D2 at C1 (2.0 ± 0.0 SE), IM (5.3 ± 1.9 SE) and C2 (5.5 ± 2.5 SE) were lower than those recorded at these locations during the Baseline Phase (C1 7.0, IM , C2-9.3). Dugong population estimates during D2, derived from the Marsh and Sinclair (1989a) and Pollock et al. (2006) methods, were 99 ± 48 SE and 90 ± 37 SE in IM, and 93 ± 45 SE and 67 ± 26 SE in C2, respectively. No population estimates could be calculated for C1 during D2 as there were too few dugong sightings. Population estimates derived from the Marsh and Sinclair (1989) and Pollock et al. (2006) methods during D2 for IM (99 ± 48 SE and 90 ± 37 SE) and C2 (93 ± 45 SE and 67 ± 26 SE) were lower than the average recorded during the Baseline Phase for IM (359 ± 147 SE and 231 ± 106 SE) and C2 (227 ± 74 SE and 148 ± 82 SE). Dugong population estimates during D2 and throughout the Baseline Phase were variable. This variability may have been as a result of the inherent behaviour of dugongs (i.e. highly mobile and constantly submerging), migration or seagrass seasonality, as well as environmental conditions experienced during aerial surveys such as changing sea states and high turbidity. During D2 the number of dugong sightings and associated population estimates were lower at all locations compared to the Baseline Phase. Prepared for INPEX Cardno iii

4 The greatest density of dugong sightings in IM during D2 were observed within the Shoal Bay and Lee Point areas. Recent seagrass mapping completed within Shoal Bay has recorded Halophila decipiens in the area (Geo Oceans 2013), which is a preferred diet of dugongs (Preen 1995). Given that an observed relationship between the distribution of dugongs and Halophila decipiens was also noted during the Baseline Phase, the presence, distribution, density and species composition of seagrass habitats is potentially important. Turtles Six hundred and twenty-seven turtles were sighted in D2 in comparison to an average of 598 turtles recorded during the Baseline Phase. The mean number of turtles sighted at C1 (91 ± 17.5 SE) was higher during D2 than the Baseline Phase (61). In contrast, the mean number of turtles sighted in IM (62.7 ± 11.0 SE) and C2 (83 ± 22.0 SE) during D2 was lower than during the Baseline Phase (IM: 84, C2: 86). However, estimated population sizes were lower at each location during D2 compared to the Baseline Phase, although variability was evident among the population estimates derived for turtles during D2 and the Baseline Phase. A decline in the densities of turtle sightings was recorded in IM across 60% of the grid cells in comparison to the Baseline Phase. Inter-survey variation in turtle densities may be a result of short-term movement in and out of specific areas, the pursuit of optimal foraging areas or an influx of turtles, for example, due to nesting activities. An increase in the density of turtle sightings in IM, specifically Middle Arm and Wickham Point, was recorded during D2 compared to a temporally similar period in the Baseline Phase. Such increases in the density of turtles may be associated with the physical characteristics, availability of suitable habitats or foraging activities within these areas. Further surveys have the potential to provide greater insight into the ongoing use of these areas by turtles within Darwin Harbour and surrounding regions. Land Surveys During May 2013, land observations were introduced to the TDMP as a replacement to boat-based surveys within Darwin Harbour and surrounding areas. Land observations were completed at Island and Cullen Bay, which were previously recognised as hotspots for marine megafauna sightings. Land surveys at identified hotspots address the second objective of the TDMP. At Island, over 100 turtles were sighted during the sampling period. Sixty-four per cent of turtles at Island were confirmed as green turtles and an estimated 89% of the total sightings were recorded as juveniles. Dive times were calculated for two juvenile green turtles at Island, with an average dive duration of ten minutes recorded for one of the juvenile turtles. At Cullen Bay, only two turtle sightings were made during the sampling period and a single dugong was sighted during a scheduled off effort sampling period. Prepared for INPEX Cardno iv

5 Glossary Term or Acromym Availability bias ACF B1, B2, B3 BHD BSS CI CL CSD CV Double platform DLPE DSDMP EBPC Act GEP GIS h HSE Definition A bias in the data affected by an animal being concealed by an environmental factor so that is not visible to the observer Availability Correction Factor Baseline Phase survey 1, Baseline Phase survey 2, Baseline Phase survey 3 Backhoe Dredger Beaufort Sea State is an empirical measure (0-12) for the intensity of the wind based mainly on seastate or wave conditions with 0 refering to calm, mirror like seas and 12 refers to hurricane conditions Confidence Interval Condifence Level Cutter Suction Dredger Coefficient of Variation is used to compare the standard deviations between populations with different means and it provides a measure of variation that is independent of the measurement units A sampling method using two observers to sample a given species in the same area at the same time. The two observers must be independent of each other and isolated visually and acoustically. On aerial surveys, the two observers are normally arranged as a front and rear observer Department of Lands, Planning and Environment Dredging and Spoil Disposal Management Plan East Arm The Commonwealth Environment Protection and Biodiversity Conservation Act (1999) Gas export pipeline Geographic Information System Hour/s Health Safety Environment Prepared for INPEX Cardno v

6 Term or Acromym IPDEP km/h kn LAT min MNES n NEMP NT NTU Paj PB PCF PERMANOVA Perception bias PF Population estimate p-perm PR QA/QC Recapture SB SE SF Definition Ichthys Project Dredging Expert Panel Kilometres per hour Knots: Nautical miles per hour Lowest Astronomical Tide Minute/s Matter of National Environmental Significance Sample size Ichthys Project Nearshore Environmental Monitoring Plan Northern Territory Nephelometric Turbidity Units Probability of availability which is used for population estimates Port observers - both front and rear Perception Correction Factor Permutational Analysis of Variance A bias in the data caused by an observer not seeing an animal despite it being visible Port observer - front only An estimate of the number of individual animals living in one place at the one time Equivalent to the traditional p-value but derived from a permutational analyses (PERMANOVA) Port observer - rear only Quality Assurance/Quality Control The event of one individual or group of animals being counted (and thus recorded) a subsequent time, usually by the rear observer during aerial surveys Starboard observers - both front and back observers Standard error of the mean Starboard observer - front only Prepared for INPEX Cardno vi

7 Term or Acromym SR TDMP Turbidity Definition Starboard observer - rear only Turtle and Dugong Monitoring Program Turbidity gives an indication of water clarity Prepared for INPEX Cardno vii

8 Table of Contents Executive Summary iii Glossary 1 Introduction Project Description Background Aims and Objectives 1 2 Methodology Sampling Locations Aerial Surveys Land Observations Monitoring Schedule Field Methods Aerial Surveys Land Observations Data Analysis Aerial Surveys Land Observations Assumptions and Constraints Aerial Surveys Land Observations Quality Assurance and Quality Control 8 3 Results Aerial Surveys Survey Effort Dugongs Turtles Land Observations Survey Effort Cullen Bay Rock Wall Quality Assurance and Quality Control 40 4 Discussion Aerial Surveys Dugongs Turtles Land Observations 42 5 Conclusions 45 6 Acknowledgements 46 7 References 47 v Prepared for INPEX Cardno viii

9 Tables Table 2-1 Monitoring schedule for the TDMP Baseline Phase 5 Table 3-1 Details of group size estimates and correction factors used in the population estimates for dugongs for D2 aerial surveys (using Marsh and Sinclair (1989) method only) 18 Table 3-2 Sighting histories for dugong groups sighted during D2 aerial surveys in May 2013 by individual observers 19 Table 3-3 Comparison of dugong population estimates for each block during D2 and the Baseline Phase based on Marsh and Sinclair (1989) and Pollock et al. (2006) 19 Table 3-4 Results of univariate PERMANOVA testing for differences in the density of dugongs per km 2 based on: a) Marsh and Sinclair (1989); and b) Pollock et al. (2006) population estimates methods between the three Baseline Phase surveys (B1, B2 and B3) among two Treatments (IM and C1/C2) 22 Table 3-5 Results of univariate PERMANOVA testing for differences in the density of dugongs per km 2 based on raw sightings between two Phases (Baseline and Dredging), Phase (B1, B2 and B3 within Baseline Phase and D2 within Dredging Phase), two Treatments (Control and Impact) and three Blocks (C1 and C2 within Control and IM within Impact) 23 Table 3-6 Details of turtle group size estimates and correction factors used in population estimates for the D2 aerial survey 31 Table 3-7 Sighting histories for turtles observed during all D2 aerial surveys by individual observers 32 Table 3-8 Comparison of Turtle population estimates for each block during D2 and the Baseline Phase based on Marsh and Sinclair (1989) and Pollock et al. (2006) methods 32 Table 3-9 Results of univariate PERMANOVA tests for differences in the density of turtles per km based on: a) the Marsh and Sinclair (1989) population estimate method; and b) the Pollock et al. (2006) population estimate method; and c) raw sightings between two Phases (Baseline and Dredging), Phase (B1, B2 and B3 within Baseline Phase and D2 within Dredging Phase), two Treatments (Control and Impact) and three Blocks (C1 and C2 within Control and IM within Impact) 35 Table 3-10 Survey effort for land-based observations during D2 37 Table 3-11 Number of marine mammal and turtle sightings from land survey sites during D2 in May Figures Figure 2-1 Aerial survey blocks encompassing Bynoe Harbour (C1), Darwin Harbour/Hope Inlet region (IM) and Vernon Islands (C2) 3 Figure 2-2 Land observation sites in Darwin Harbour during D2 - Cullen Bay Rock Wall (left) and (right) 4 Figure 3-1 Distribution of dugong sightings during D2 aerial survey 11 Figure 3-2 Mean counts per replicate (± SE) of dugongs in each block (C1, IM, C2) during D2 aerial survey. The mean number of dugongs recorded in the Baseline Phase in each block is indicated by the solid lines 12 Figure 3-3 Density of dugong sightings (based on raw counts) within 6 km x 6 km grids at IM during D2 aerial survey in May Figure 3-4 Relative difference in the density of dugong sightings (based on raw counts) within 6 km x 6 km grids in IM during D2 compared to the Baseline Phase 14 Figure 3-5 Proportion of dugong sightings within different depth (m) ranges at: a) C1; b) IM; and c) C2 during D2 and the Baseline Phase 16 Figure 3-6 Proportion of dugong sightings with respect to benthic habitat types at: a) C1; b) IM and c) C2 during D2 and the Baseline Phase 17 Prepared for INPEX Cardno ix

10 Figure 3-7 Mean population estimates for dugongs in each block during D2 and the Baseline Phase based on: a) Marsh and Sinclair (1989); and b) Pollock et al. (2006) population estimate methodologies 20 Figure 3-8 Mean dugong density per km 2 (±SE) at each location during D2 and the Baseline Phase based on: a) Marsh and Sinclair population estimate method; b) Pollock et al. population estimate method; and c) raw sightings 21 Figure 3-9 Distribution of turtles during D2 aerial survey in May Figure 3-10 Mean counts per replicate (±SE) of turtles in each block (C1, IM, C2) during D2. The mean number of turtles recorded during the Baseline Phase at each block is indicated by the solid line 25 Figure 3-11 Density of turtle sightings (based on raw counts) within 6 km x 6 km grids at IM during D2 aerial survey in May Figure 3-12 Relative difference in the density of turtle sightings (based on raw counts) within 6 km x 6 km grids at IM during D2 compared to the Baseline Phase 27 Figure 3-13 Proportion of turtle sightings within different depth (m) ranges at: a) C1; b) IM; and c) C2 during D2 and the Baseline Phase 29 Figure 3-14 Proportion of turtle sightings with respect to benthic habitat types at: a) C1; b) IM; and c) C2 during D2 and the Baseline Phase 30 Figure 3-15 Mean population estimates turtles within each block during D2 and the Baseline Phase based on: a) Marsh and Sinclair (1989); and b) Pollock et al. (2006) population estimate methodologies 33 Figure 3-16 Mean turtle density per km 2 (±SE) at each location during D2 and the Baseline Phase based on: a) the Marsh and Sinclair population estimate method; b) the Pollock et al. population estimate method; and c) raw sightings 36 Figure 3-17 Distribution of marine mammal and turtle sightings from land-based sites during D2 in May Appendices Appendix A Summary of Aerial Survey Effort During Baseline and Dredging Phase Surveys Appendix B Tidal Ranges and Dugong Densities for Dredging and Baseline Phase Aerial Surveys Appendix C Summary of Dugong Sightings across Dredging and Baseline Phase surveys Appendix D Dugong Regional Relative Densities During Baseline Phase Surveys Appendix E Distribution of Dugongs and Turtles Recorded Across IM Block During Dredging and Baseline Phase surveys Appendix F Dugong Population Size Estimates During Dredging and Baseline Phase Surveys Appendix G Corrected Dugong Densities During Dredging and Baseline Phase Surveys Appendix H Dugong Group Size Data for Population Estimate Calculations Appendix I Summary of Turtle Sightings Across Dredging and Baseline Phase Surveys Appendix J Dugong Regional Relative Densitites During Baseline Phase Surveys Appendix K Turtle Population Size Estimates During Dredging and Baseline Phase surveys Appendix L Turtle Group Size Data for Population Estimate Calculations Appendix M Corrected Turtle Densities During Dredging and Baseline Phase Surveys Appendix N Tidal Ranges and Turtle Densities for Dredging and Baseline Phase Aerial Surveys Appendix O Land-based Observation Sightings Data Prepared for INPEX Cardno x

11 1 Introduction 1.1 Project Description INPEX is the operator of the Ichthys Gas Field Development Project (the Project). The Project comprises the development of offshore production facilities at the Ichthys Field in the Browse Basin, some 820 km westsouth-west of Darwin, an 889 km long subsea gas export pipeline (GEP) and an onshore processing facility and product loading jetty at Blaydin Point on Middle Arm Peninsula in Darwin Harbour. To support the nearshore infrastructure at Blaydin Point, dredging works will be carried out to extend safe shipping access from near East Arm Wharf to the new product loading facilities at Blaydin Point which will be supported by piles driven into the sediment. A trench will also be dredged to seat and protect the GEP for the Darwin Harbour portion of its total length. Dredged material will be disposed at the spoil ground located approximately 12 km north-west of Lee Point. A detailed description of the dredging and spoil disposal methodology is provided in Section 2 of the Dredging and Spoil Disposal Management Plan East Arm (DSDMP) (INPEX 2012). 1.2 Background This report outlines the findings of the second Dredging Phase survey of the Turtle and Dugong Monitoring Program (TDMP) undertaken in May 2013 (D2). It contains results from aerial surveys and land-based observations and compares these data with those collected during the Baseline Phase. Baseline Phase survey 3 (B3) was undertaken after the commencement of the Backhoe Dredger (BHD) operations on 27 August 2012 and originally termed Dredging Phase survey 1 (D1); however, given this was prior to the start of the Cutter Suction Dredger (CSD) on 4 November, it was renamed B3. This was further supported by statistical analyses, which found no statistical difference between the three surveys. As the May 2013 survey (D2) was the first survey during the Dredging Phase for the TDMP, the survey and subsequent results obtained from this period will be referred to as D2. The field protocol utilised in this program follows the methodology outlined in the Nearshore Environmental Monitoring Plan (NEMP) (Cardno 2012d). 1.3 Aims and Objectives The key objectives of the TDMP are to: > Quantify the variability of turtle and dugong relative abundance and distribution in the inshore waters of Darwin Harbour and nearshore waters between and within surveys. Observe changes in these parameters over the duration of the dredging and post dredging periods; and > Assess fine scale aspects of dugong and turtle populations within Darwin Harbour in relation to potential habitat use and identify foraging areas (if possible). The aim of this Report was to continue collection of robust data on turtle and dugong distribution and abundance around the monitoring area during the Dredging Phase that can then be used for temporal comparison with data collected during the Baseline Phase. Prepared for INPEX Cardno 1

12 2 Methodology Full details on methodology for aerial surveys and turtle tagging for the TDMP can be found in Appendix K of the NEMP (L384-AH-PLN-0003) and the TDMP Baseline Report and Dredging 1 Report (Cardno 2012c, 2013). Where methodology has been refined, or when there has been additional analysis utilised, details are provided. 2.1 Sampling Locations Aerial Surveys Aerial surveys were used to collect data over a broad spatial scale from three geographical regions (or blocks) (Figure 2-1): > Block 1 Bynoe Harbour (Control location 1 C1); > Block 2 encompassing Darwin Harbour/Hope Inlet to Gunn Point (Impact location - IM); and > Block 3 located to the east, from Gunn Point and the Vernon Islands and across to Melville Island (Control location 2 C2) Land Observations Data collected during the Baseline Phase boat surveys in 2012 indicated that vessel transects and point sampling methods resulted in very low observations for the effort with little additional yield of finer-scale data of turtles or dugongs around Darwin Harbour compared to the aerial surveys. Therefore, it was proposed by the Ichthys Project Dredging Expert Panel (IPDEP) that land observations from recognised hotspots around Darwin Harbour (discreet areas with potentially the highest number of marine fauna sightings) be introduced to replace vessel transects and point sampling. These hotspots would allow for longer observation periods and greater likelihood of encountering turtles or dugongs than vessel-based surveys, thus allowing more insight into finer-scale behaviour of turtles and dugongs. A review of historical sighting data, as well as consultation with local experts in the region, identified hotspots within the region to assist in finding suitable locations for land-based observations for turtles and dugongs. In D2, land observations were undertaken from two locations around Darwin Harbour - Island Bridge and Cullen Bay Rock Wall (Figure 2-2) - in order to assess finer scale aspects of turtle and dugong populations within Darwin Harbour in relation to habitat at frequently used areas. Prepared for INPEX Cardno 2

13 C2 IM C1 Figure 2-1 Aerial survey blocks encompassing Bynoe Harbour (C1), Darwin Harbour/Hope Inlet region (IM) and Vernon Islands (C2) Prepared for INPEX Cardno 3

14 Figure 2-2 Land observation sites in Darwin Harbour during D2 - Cullen Bay Rock Wall (left) and (right) Prepared for INPEX Cardno 4

15 2.2 Monitoring Schedule Survey D2 was undertaken in May 2013, following three Baseline Phase surveys undertaken in Table 2-1 outlines the monitoring schedule for the Baseline and Dredging Phases during the TDMP. Table 2-1 Monitoring schedule for the TDMP Baseline Phase Sampling Periods Baseline Phase Dredging Phase Field Method Site B1 B2 B3 D2 Aerial survey Darwin Harbour and surrounding waters Aerial Surveys (May/June 2012) Training and Safety Inductions 7 days, 2 replicate flights Aerial Surveys (July/August 2012) Training and Safety Inductions 14 days, 3 replicate flights Aerial Surveys (September/ October 2012) Training and Safety Inductions 17 days, 3 replicate flights Aerial Surveys (May 2013) Training and Safety Inductions 16 days, 2-3 replicate flights* Boat surveys Darwin Harbour and surrounding waters Transects and Point-Sampling (June/ July 2012) Training and Safety Inductions 6 days, 1 replicate of 15 point sampling sites and transects between sites Transects and Point-Sampling (August 2012) Training and Safety Inductions 11 days, 1 replicate of 20 point-sampling sites and transects between sites, 2 nd replicate of area from Lee Point to Vernon Islands Point-Sampling (October 2012) Training and Safety Inductions 10 days, 2 replicate of 20 point sampling sites No boat transects Land surveys Land observations (May 2013) Island Bridge Cullen Bay Rock Wall 4 days 1 x satellite tagging event, on foot Turtle tagging Island Bridge (September/ October 2012) 6 days 1 x satellite tagging event, net capture via boat (Nov 2012) 4 days Casuarina Beach 1 x satellite tagging event (September/ October 2012) 13 nights * D2 surveys: C1 and IM blocks: 3 replicate flights; C2: 2 replicate flights Prepared for INPEX Cardno 5

16 2.3 Field Methods Aerial Surveys The aerial survey methodology followed the established strip transect aerial survey design technique (Marsh and Sinclair 1989). A Dornier 220 aircraft was used for the D2 aerial surveys. This was a different aircraft than that used for the Baseline Phase surveys (Casa 212), although the Dornier 220 has the same characteristics as the Casa 212 (i.e. high winged, turbine engine, twin pilots) and was flown at the same speed (approximately 110 kn) and at an altitude of 500 ft. Aerial surveys of marine megafauna were flown in three geographical survey blocks (refer to Section 2.1.1, Figure 2-1). Dolphins, dugongs and turtles were sighted and recorded in the surveys; however, it should be noted that dolphins were not reported as part of the TDMP. Raw data pertaining to dolphins sighted during aerial surveys will be supplied to the Department of Land Resources, Planning and Environment (DLRM). D2 surveys were undertaken from 9 May 2013 to 27 May Three replicate surveys were completed in C1 and IM, and two surveys in C2. A third replicate of C2 was not possible due to persistent unsuitable weather conditions for surveying. Further details of the aerial survey methods are given in the TDMP Baseline Report (Cardno 2012c) Land Observations Land observations were conducted at and Cullen Bay Rock Wall during D2. At each location, a total of eight hours of observations were undertaken per day for two days. Survey periods incorporated eight 30-minute observations, each separated by a 15 minute ( off effort ) window. During each observation period, observers continuously visually scanned the water (aided by polarised sunglasses) and reviewed water disturbance with the aid of binoculars. Surveys were initiated when the Beaufort Sea State (BSS) was less than or equal to three to maximise observability of turtles and dugongs, as well as other marine wildlife such as inshore dolphins. Environmental and water variables (BSS, glare and turbidity) were recorded at the start and end of each observation period and the position of each observer was recorded using a hand-held GPS and recorded on datasheets. The 30 minute observation period provided a record of the number of sightings in each observation period. Where possible, sightings were distinguished as individuals; however, individual recognition was generally not possible for turtles or dugongs. When an animal was sighted, information was recorded on a datasheet by each observer. If more than one animal was sighted at any one time, the focus was on gathering data for the first animal sighted. Identification rankings were given for each animal sighted with a ranking of certain, probable or uncertain given for both the type of animal recorded and the certainty of the species identified. For each sighting, information collected included the following parameters: > Date and time of each sighting; > Animal type: turtle, dugong or other incidental sightings (including an identification ranking e.g. certain, probable or uncertain). Species identification was also attempted and ranked certain or uncertain; > Number of individuals; > Bearing of sighting from the observer (using compass and/or binoculars); > Estimated distance from observer to animal; > Activity or sighting cue; > Surface time (for each surfacing); and > Dive time (N.B. if an individual was not recognisable as the same individual, dive duration was not possible) Two observers were used per survey at (Figure 2-2). The first observer was positioned on the northern side of the bridge observing north, while the second observer was located on the Prepared for INPEX Cardno 6

17 southern side of the bridge observing to the south. Each observer was situated in the middle of the bridge and observed the width of the channel on their observation side. Each observer scanned the water continuously for a 30-minute period using binoculars and the naked eye Cullen Bay Rock Wall Two observers were used per survey at the Cullen Bay Rock Wall. The observers were located at the beach end of the rock wall. One person observed the easterly to north quadrant, while the other observed the western to north quadrant. Each observer scanned the water continuously for a 30-minute period using binoculars and the naked eye. 2.4 Data Analysis Aerial Surveys Dugong and Turtle Population Estimates Dugong and turtle population estimates were calculated using methods described in Marsh and Sinclair (1989) and Pollock et al. (2006). Both of these population estimate methods correct for perception and availability biases associated with aerial visual surveys (Cardno 2012c). Population estimates were calculated for each block when five or more animals were sighted in a replicate flight. Marsh and Sinclair (1989) and Pollock et al. (2006) population estimates as well as density estimates derived from raw sighting data were used in subsequent statistical analyses Statistical Analysis Dugongs Spatial and temporal differences in dugong densities per km 2 (in raw form and as calculated from the population estimate methods of Marsh and Sinclair (1989) and Pollock et al. (2006)) were investigated using permutational univariate analyses of variance (PERMANOVA; Anderson 2001), using Euclidean dissimilarity resemblance matrices with unrestricted data permutation methodology. As there were very few dugong sightings in D2 and only one population estimate could be calculated for IM and C2, statistical analyses of the density of dugongs based on population estimation methods were restricted to analyses of the Baseline Phase. There were two factors in the analysis of density of dugongs based on population estimation methods. These were: > Survey (fixed): B1, B2 and B3; and > Treatment (fixed orthogonal): 2 levels (Impact, Controls). There were four factors in the analysis of density of dugongs based on raw data. These were: > Phase (fixed, orthogonal): 2 levels (Baseline Phase and Dredging Phase, equivalent to the Before After comparison in BACI); > Survey (random, nested within Phase): B1, B2 and B3 within Baseline Phase and D2 within Dredging; > Treatment (fixed orthogonal): 2 levels (Impact, Controls); and > Block (random, nested within Treatment): 1 (IM) and 2 levels (C1, C2). For each of the above analyses, pooling of lower-level terms with the residual term was done where appropriate (i.e. if the p- value of pooled term was 0.25). Results for both the pooled and the un-pooled versions were presented where applicable. Where a term (factor or interaction) was significant at p 0.05, pair-wise comparisons were used in post hoc analyses to identify between which levels of factors or interaction strata were significantly different. Prepared for INPEX Cardno 7

18 Turtles Turtle density estimates were derived from Marsh and Sinclair (1989) and Pollock et al. (2006) population estimation methods as well as from raw sighting data for each block during D2 and the Baseline Phase. Permutational univariate analyses using Euclidean dissimilarity resemblance matrices with unrestricted data permutation methodology (PERMANOVA; Anderson 2001) on untransformed density per km 2 data were used to test for differences in the density of turtles per kilometre among factors. Data for these analyses were derived from the three methods described above. The four factors examined within the permutational univariate analyses were: > Phase (fixed, orthogonal): 2 levels (Baseline and Dredging, equivalent to the Before After comparison in BACI); > Survey (random, nested within Phase): B1, B2 and B3 within Baseline Phase and D2 within Dredging Phase; > Treatment (fixed orthogonal): 2 levels (Impact, Controls); and > Block (random, nested within Treatment): 1 (IM) and 2 levels (C1, C2). Pooling of lower-level terms with the residual terms and post hoc analytical procedures were the same as those outlined for dugongs (see Section ) Land Observations Variability in the data arising from several sources, including variability in sea state, observing conditions, temporal changes and movements of the animals themselves resulted in a reduced statistical power to detect change. Land-based data have therefore been presented in a tabular format with spatial representation of sightings in the form of GIS mapping. 2.5 Assumptions and Constraints Aerial Surveys Wind was a constraint during D2, with the BSS calculated to be between BSS 3 and BSS 4, 47% of the time, resulting in the completion of two replicates for C2 (a complete set of three replicate flights for both C1 and IM block were completed). This differed to the same time during the Baseline Phase where survey conditions and visibility were suitable throughout the survey, with an average of BSS = 2 (Cardno 2012c). Flights during this survey were often conducted either in the early morning or late afternoon to avoid times during the middle of the day, which could potentially impede the ability to sight animals due sun angles and increased glare. During D2, a new plane was used (refer to Section 2.3.1); however, speed and operational constraints were the same as during the Baseline Phase surveys and were monitored continuously during D2 through communication between the co-pilot and environmental data collector so no constraints were incurred Land Observations Similar to boat-based surveys, an unavoidable constraint with the land-based surveys was the inability to successfully undertake a mark-recapture of animals (turtles or dugongs). In delphinids, this is possible by photographing individual markings on their dorsal fins ( mark ), which allows the animal to be re-identified during subsequent surveys ( recapture ). Therefore, the total number of sightings is likely to be greater than the actual number of individuals observed. 2.6 Quality Assurance and Quality Control Aerial survey observation data were transcribed and entered into an Access database post flight. Ten per cent of entries were randomly checked by observer teams and environmental data checked by the Environmental data collector. Once compiled, a final Quality Assurance (QA) process was undertaken by the survey leader in the master database, with 10% of the total number of transects flown randomly checked. Prepared for INPEX Cardno 8

19 Land survey data were recorded on datasheets and entered into an Excel spread sheet at the end of each sampling period. All entries were checked for completeness against field sheets and any missing cells or information. Ten per cent of edited files were checked for errors by random selection. Prepared for INPEX Cardno 9

20 3 Results 3.1 Aerial Surveys Survey Effort In total, 2,466 linear kilometres were flown over an approximate 38 hour period during D2, with 19:08 hours on transect. The total length of transects over water was 1,358.5 km, equating to an area of km 2 (based on a transect width of 400 m). The overall monitoring area (variable due to tidal level) was 2,974 km 2 across all three geographical blocks (Appendix A). Approximately 18% of the available area was surveyed across the three blocks. Tidal ranges for each of the replicate flights during D2 are given in Appendix B. Survey conditions and visibility were variable throughout D2. Turbidity was an average of 4 (based on a standardised turbidity scale used in aerial surveys, which refers to highly turbid water as reported in Hodgson et al. (2011)) across all surveyed blocks with BSS between 3 and 4, 47% of the time. In general, the wind was higher during D2 (BSS 3) compared to the Baseline Phase (average BSS = 2). Transects flown on each day were selected according to conditions, allowing for the best possible sampling conditions within each block (Figure 2-1) Dugongs Sightings and Distribution The distribution of dugong sightings during D2 within each block is presented in Figure 3-1. Dugong sightings were lower across all three survey blocks in D2 compared to the Baseline Phase. During D2, 33 dugongs were sighted (all flights, in all survey blocks and replicates) compared with an average of 88 dugongs recorded during the Baseline Phase (B1, n = 58; B2, n = 92; B3, n = 113). During D2 in C1 and C2, six and 11 dugongs were sighted respectively (C1: Rep 1 = 2 dugongs, Rep 2 = 2 dugongs, Rep 3 = 2 dugongs; C2 Rep 1 = 3 dugongs, Rep 2 = 8 dugongs). The greatest number of dugong sightings recorded during D2 (16 dugongs) was in IM (Rep 1 = 3 dugongs, Rep 2 = 4 dugongs, Rep 3 = 9 dugongs). On average, 19 and 25 dugongs were recorded in C1 and C2 respectively during surveys conducted in the Baseline Phase (Appendix C). The distributions of dugong sightings at C1 and C2 were generally similar between D2 and the Baseline Phase (Cardno 2012c). Based on raw sighting data, the mean number of dugongs sighted during D2 within each block (C1 = 2, IM = 5.3, C2 = 5.5), was lower compared to the mean number recorded during the Baseline Phase (C1 = 7, IM = 16.6, C2 = 9.3) (Figure 3-2). Dugong sightings within each block during D2 consisted predominantly of adult dugongs. One cow/calf pair was sighted in IM during D2. At a similar time during the Baseline Phase, calves were sighted in each of the blocks, with two calves recorded at IM (Appendix C). During D2, a high proportion of dugong sightings in IM, and consequently the density of dugongs sighted based on raw sightings within designated 6 km x 6 km grids, were recorded within Shoal Bay and habitats around Lee Point (grid cells 21, 22 and 28, Figure 3-3). These finding are generally consistent with those reported during the Baseline Phase (Appendix D). During D2, dugong sightings at IM within Shoal Bay, around Lee Point and Charles Point (grid cell 9) were within the vicinity of recently mapped seagrass (Figure 3-3, Appendix E) (Geo Oceans 2012, 2013). During D2, the density of dugong sightings, based on raw counts, at IM increased in 14% of grid cells (grid cells 3, 4, 21, 28, 30 and 42) compared to the Baseline Phase (Figure 3-4). In contrast, 56% (24 grid cells) displayed a decrease in dugong densities compared to the Baseline Phase (Figure 3-4). Thirty per cent of grid cells at IM have had no reported sightings of dugongs during either D2 or the Baseline Phase (Figure 3-4). Prepared for INPEX Cardno 10

21 Figure 3-1 Distribution of dugong sightings during D2 aerial survey Prepared for INPEX Cardno 11

22 18 Mean dugong count + SE C1 IM C2 Location Figure 3-2 Mean counts per replicate (± SE) of dugongs in each block (C1, IM, C2) during D2 aerial survey. The mean number of dugongs recorded in the Baseline Phase in each block is indicated by the solid lines Prepared for INPEX Cardno 12

23 Figure 3-3 Density of dugong sightings (based on raw counts) within 6 km x 6 km grids at IM during D2 aerial survey in May 2013 Prepared for INPEX Cardno 13

24 Figure 3-4 Relative difference in the density of dugong sightings (based on raw counts) within 6 km x 6 km grids in IM during D2 compared to the Baseline Phase Prepared for INPEX Cardno 14

25 Dugong Bathymetric Distribution and Habitat Associations During D2, dugongs were sighted in waters up to a depth of 24 m (not corrected for tides). Over the entire survey area, 94% of all dugongs were sighted in waters less than 20 m in depth, with 70% of those sightings occurring in water less than 5 m in depth (C1: 100%, C2: 27%, IM: 88%). This was consistent with sightings during the Baseline Phase, where 62% of all dugongs were sighted in waters less than five meters deep. A higher proportion of dugongs sighted were recorded within the 0 m to 5 m depth range at C1 and IM during D2 compared to the Baseline Phase. Dugongs were most frequently sighted in the 6 m to 10 m depth range at C2 during D2. Dugongs sighted at C2 were distributed more evenly among depth ranges than at C1 or IM. The depth distributions of sighted dugongs were generally consistent within each block between D2 and the Baseline Phase (Figure 3-5). All dugong sightings at C1 during D2 were reported over unknown benthic habitat. The proportion of dugongs sighted over unknown habitat type was similar to that reported during the Baseline Phase. In IM, 69% of dugong sightings were recorded over sand habitat, 19% in unknown habitat types and 6% recorded in reef and seagrass habitats (Figure 3-6). In comparison, the majority (55%) of dugongs at C2 were sighted over reef habitats with a further 45% of dugongs sighted over unknown habitat types (Figure 3-6). Prepared for INPEX Cardno 15

26 1 a) C1 Baseline Phase 0.8 D Proportion of dugong sightings b) IM Baseline Phase D2 1 c) C2 Baseline Phase 0.8 D Depth range (m) Figure 3-5 Proportion of dugong sightings within different depth (m) ranges at: a) C1; b) IM; and c) C2 during D2 and the Baseline Phase Prepared for INPEX Cardno 16

27 1 0.8 a) C1 Baseline Phase D Proportion of dugong sightings b) IM Baseline Phase D c) C2 Baseline Phase D Mangrove Unknown Reef Sand Seagrass Benthic habitat types Figure 3-6 Proportion of dugong sightings with respect to benthic habitat types at: a) C1; b) IM and c) C2 during D2 and the Baseline Phase Prepared for INPEX Cardno 17

28 Estimates of Dugong Population Size Mean group sizes, Perception Correction Factors (PCFs) and Availability Correction Factors (ACFs) used for estimating the size of the dugong populations in the aerial survey blocks C1, IM and C2 during each survey using the Marsh and Sinclair (1989) method only are presented in Table 3-1. It should be noted that all parameter estimates in Table 3-1 were based on all sightings, including those in the inside and outside zones, which refers to sightings inside or outside the 200 m transect on each side of the plane. Due to the small number of sightings, PCFs and ACFs were calculated using all dugong sightings during D2, while group sizes and coefficients of variation (CV) were calculated for each replicate flight where there were 5 individual sightings to derive population estimates. For calculation of PCF values using the Marsh and Sinclair (1989) method and for modelling of perception bias in MARK (program used in the calculation of population estimates) prior to performing the Pollock et al. (2006) population estimates, surveys were pooled by block instead of by replicate flight as in previous surveys. Unlike previous surveys conducted within the Baseline Phase, D2 surveys were performed with the same observer team for each replicate flight and replicates of each block were flown in a haphazard manner, not in chronological order. This, in combination with the lack of a third replicate for the C2 block and the similar environmental conditions within each block between replicate flights, was the reasoning for pooling D2 surveys in this manner for these calculations. As with previous analyses, group size and its CV were determined for each replicate flight. Table 3-1 Details of group size estimates and correction factors used in the population estimates for dugongs for D2 aerial surveys (using Marsh and Sinclair (1989) method only) Survey Block Replicate Mean group size (CV) PCF (CV) ACF (CV) Starboard Port C D2 May 2013 IM (0.22) 1.03 (0.02) 1.08 (0.06) 2.36 (0.24) (0.25) N/A C (0.02) 1.08 (0.06) 2.36 (0.24) -- No mean group size or CV calculated due to 5 sightings; N/A no 3 rd replicate flight flown in C2 Prepared for INPEX Cardno 18

29 Table 3-2 Survey Sighting histories for dugong groups sighted during D2 aerial surveys in May 2013 by individual observers Rep No. Number of dugong groups seen by: Total # dugong groups sighted % dugong groups sighted by both observers SF SR SB PF PR PB S'board Port D % 0% % 67% % 33% Combined D % 43% Starboard front (SF); starboard rear (SR); starboard both (SB); port front (PF); port rear (PR) and port both (PB); N.B. all dugong sightings combined were used for estimates of perception and availability correction factors in D2 survey. Due to the low number of sightings during D2 (Table 3-2), population estimates could only be calculated for the third replicate flight at IM and the second replicate flight at C2. A population estimate was not calculated for C1 in D2. The estimated population size of dugongs at IM was 90 ±37 SE and 99 ± 48 SE based on the Pollock et al. (2006) and Marsh and Sinclair (1989) methods respectively. In C2, dugong population estimates during D2 were 67 ±26 SE and 93 ±45 SE based on the Pollock et al. (2006) and Marsh and Sinclair (1989) methods respectively (Table 3-3). Mean population estimates derived in IM and C2 during D2 were lower than those reported during the Baseline Phase (Figure 3-7, Appendix F). Whilst population estimates can be calculated based on any number of sightings (including n = 1), it is recognised that the variance associated with these estimates would be large, reducing the reliability of the population estimate calculated. Therefore, population estimates were only undertaken for replicate flights when greater than five sightings were recorded (i.e. IM and C2). Table 3-3 Comparison of dugong population estimates for each block during D2 and the Baseline Phase based on Marsh and Sinclair (1989) and Pollock et al. (2006) N.B. insufficient data were available for population estimates to be made for C1 in D2 Baseline Phase D2 Estimation Method Block Est. SE Est. SE Marsh and Sinclair C IM C Pollock et al. C IM C Prepared for INPEX Cardno 19

30 600 a) Marsh and Sinclair Baseline Phase D2 300 Mean population estimate + SE b) Pollock et al. Baseline Phase D C1 IM C2 Location Figure 3-7 Mean population estimates for dugongs in each block during D2 and the Baseline Phase based on: a) Marsh and Sinclair (1989); and b) Pollock et al. (2006) population estimate methodologies N.B. insufficient data were available for population estimates to be made for C1 in D Dugong Density As per population estimations (see Section ), the density of dugongs per km 2 was calculated for the second and third replicate flights at C2 and IM respectively during D2. No densities were calculated for dugongs at C1 due to the low number of sightings recorded in this block during D2. The mean density of dugongs per km 2 ranged between 0.08 ± 0.03 SE to 0.09 ± 0.04 SE at IM and between 0.07 ± 0.03 SE to 0.09 ± 0.04 SE at C2, based on the Pollock et al. (2006) and Marsh and Sinclair (1989) population estimate methods respectively. Based on the two population estimate methods, mean dugong densities at IM and C2 were lower during D2 compared to the Baseline Phase (Figure 3-8; Appendix G). Raw data used for the calculation of population estimates and densities are presented in Appendix H. Prepared for INPEX Cardno 20

31 Figure 3-8 Mean dugong density per km 2 (±SE) at each location during D2 and the Baseline Phase based on: a) Marsh and Sinclair population estimate method; b) Pollock et al. population estimate method; and c) raw sightings N.B. insufficient data were available for population estimates to be made for C1 in D2 Prepared for INPEX Cardno 21

32 Based on Marsh and Sinclair (1989) population estimates, no significant difference in the mean density of dugongs was detected between Surveys within the Baseline Phase irrespective of Treatment or among Treatments irrespective of Survey (Table 3-4). A significant Survey x Treatment interaction (p = 0.04) was detected in the mean density of dugongs based on Pollock et al. (2006) population estimates (Table 3-4). Pairwise comparisons revealed that the mean density of dugongs per km 2 in Control locations (C1 and C2) was significantly higher during B2 (0.39 ± 0.17 SE) compared to B1 (0.12 ± 0.02 SE) and B3 (0.12 ± 0.04 SE). There were no significant differences in the mean density of dugongs per km 2 within Control locations between B1 (0.12 (± 0.02 SE) and B3 (0.12 (± 0.04 SE). Similarly, no significant differences in the mean density of dugongs per km 2 were detected between the Control (C1 and C2) and Impact (IM) locations during any particular Survey within the Baseline Phase (Table 3-4). No significant Phase x Treatment interaction was detected for the density of dugongs derived from raw sightings (Table 3-5). In addition, there was no difference in the mean density of dugongs among Treatments within Phases and between Phases within Treatments. There were also no significant differences between Phases (irrespective of Treatment) and Treatment (irrespective of Phase) indicating that the density of dugongs did not significantly differ from D2 to the Baseline Phase or between Control (C1 and C2) and Impact (IM) locations (Table 3-5). Table 3-4 Results of univariate PERMANOVA testing for differences in the density of dugongs per km 2 based on: a) Marsh and Sinclair (1989); and b) Pollock et al. (2006) population estimates methods between the three Baseline Phase surveys (B1, B2 and B3) among two Treatments (IM and C1/C2) ( ) Pooled with those for the Residual term in final analysis RED Redundant, as lower order interactions differed significantly Source of Variation df MS Pseu-F p-(perm) df MS Pseu-F p-(perm) a) Marsh and Sinclair b) Pollock et al. Survey RED Treatment < RED Survey x Treatment (2) (0.01) (1.54) Residual/Pooled 13 < <0.01 Total <0.01 Pairwise Comparisons (ranked from largest (left) to smallest (right) Control: B2 > B1 Control: B1 = B3 Control: B2 > B3 IM: B2 = B1 IM: B1 = B1 IM: B3 = B2 B1: IM = Control B2: Control = IM B3: IM = Control Prepared for INPEX Cardno 22

33 Table 3-5 Results of univariate PERMANOVA testing for differences in the density of dugongs per km 2 based on raw sightings between two Phases (Baseline and Dredging), Phase (B1, B2 and B3 within Baseline Phase and D2 within Dredging Phase), two Treatments (Control and Impact) and three Blocks (C1 and C2 within Control and IM within Impact) ( ) Pooled with those for the Residual/Pooled term in the final analysis Source of Variation df MS Pseu-F p-(perm) Raw sightings Phase 1 < Treatment 1 < Phase x Treatment 1 < Survey(Phase) 2 < Block(Treatment) 1 < Phase x Block(Treatment) 1 < Treatment x Survey(Phase) 2 < Survey(Phase) x Block(Treatment) (2) (<0.01) (0.40) 0.67 Residual/Pooled 26 <0.01 Total 31 Pairwise Comparisons (ranked from largest (left) to smallest (right) Turtles Sightings and Distribution Baseline: B2 = B1 Baseline: B3 > B1 Baseline: B3 > B2 Treatment: Control > Impact Six hundred and twenty seven turtles were sighted across all three survey blocks during D2. Observations consisted mainly of individual turtle sightings; however, groups with more than one individual were recorded across all three survey blocks, with one group of five individuals recorded in C1 (Appendix I). The distribution of turtle sightings recorded during D2 is presented in Figure 3-9. During D2 the distributions of turtle sightings were similar to those recorded during surveys completed within the Baseline Phase (Cardno 2012c, 2013). In D2, the mean number of turtle sightings per replicate flight at C1 was higher (91 ±17.5 SE) than for the Baseline Phase (Figure 3-10). In contrast, the mean number of turtle sightings per replicate flight in IM (62 ± 11.0 SE) was lower in D2 compared to the Baseline Phase. The mean number of turtle sightings per replicate flight at C2 was comparable between D2 (83 ±22.0 SE) and the Baseline Phase (Figure 3-10). A high proportion of turtle sightings and subsequent densities within designated 6 km x 6 km grids at IM during D2 were recorded within Darwin Harbour and the north-eastern edge of Shoal Bay (Figure 3-11). The density of turtle sightings in offshore grids (e.g. 2-6) and those near the centre of Shoal Bay (e.g. 13, 14, 22 and 23) were low relative to sightings in other grids at IM during D2 (Figure 3-11). The distribution of areas of high and low turtle sighting densities at IM during D2 were generally similar to those recorded during surveys completed within the Baseline Phase (Cardno 2012c, 2013). During D2, the density of turtle sightings at IM, based on raw counts, increased in 35% of grid cells (15 grid cells) compared to the Baseline Phase (Figure 3-12, Appendix J). In contrast, 60% (26 grid cells) displayed a decrease in turtle sighting densities during D2 compared to the Baseline Phase (Figure 3-12). Two grid cells (5%) had no change in the density of turtle sightings between D2 and the Baseline Phase (Figure 3-12). Prepared for INPEX Cardno 23

34 Figure 3-9 Distribution of turtles during D2 aerial survey in May 2013 Prepared for INPEX Cardno 24

35 120 Mean turtle count + SE C1 IM C2 Location Figure 3-10 Mean counts per replicate (±SE) of turtles in each block (C1, IM, C2) during D2. The mean number of turtles recorded during the Baseline Phase at each block is indicated by the solid line Prepared for INPEX Cardno 25

36 Figure 3-11 Density of turtle sightings (based on raw counts) within 6 km x 6 km grids at IM during D2 aerial survey in May 2013 Prepared for INPEX Cardno 26

37 Figure 3-12 Relative difference in the density of turtle sightings (based on raw counts) within 6 km x 6 km grids at IM during D2 compared to the Baseline Phase Prepared for INPEX Cardno 27

38 Turtle Bathymetric Distribution and Habitat Associations Turtles were sighted across all depth ranges within each block during D2. At C1, 74% of all turtles were observed in water depths between 0 m and 5 m. The majority of turtle sightings at IM (44%) and at C2 (58%) were also recorded in this shallow depth range (Figure 3-13). The depth distributions of turtle sightings recorded during D2 at each block were similar to those reported during the Baseline Phase (Figure 3-13). During D2, turtles sighted at C2 were observed in water depths almost 50 m deep which were associated with deep channel habitats near the Vernon Islands. The majority of turtle sightings at C1 (94%), C2 (79%) and IM (56%) were reported over unknown (i.e. unsurveyed) habitat types during D2 (Figure 3-14) and this is consistent with these habitat types having the greatest representation within locations. Given the great proportion of unsurveyed areas in locations, particularly C1 and C2, it is impossible to determine turtle preferred habitat from the aerial survey data. No turtle sightings were recorded at C1 over mangrove, reef or seagrass habitats, while 6% of sightings at C1 were made over sand habitats during D2. Of the known habitats in IM, 24% turtles were sighted over sand, 18% on reef and 2% on seagrass (Figure 3-14). The habitat associations of turtle sightings within each block during D2 are consistent with those observed during the Baseline Phase (Figure 3-14). Prepared for INPEX Cardno 28

39 1 0.8 a) C1 Baseline Phase D Proportion of turtle sightings b) IM Baseline Phase D c) C2 Baseline Phase D Depth range (m) Figure 3-13 Proportion of turtle sightings within different depth (m) ranges at: a) C1; b) IM; and c) C2 during D2 and the Baseline Phase Prepared for INPEX Cardno 29

40 1 0.8 a) C1 Baseline Phase D Proportion of turtle sightings b) IM Baseline Phase D2 1 c) C2 Baseline Phase 0.8 D Mangrove Unknown Reef Sand Seagrass Benthic habitat types Figure 3-14 Proportion of turtle sightings with respect to benthic habitat types at: a) C1; b) IM; and c) C2 during D2 and the Baseline Phase Prepared for INPEX Cardno 30

41 Estimates of Turtle Population Size Details of the mean group sizes and correction factors used for estimating turtle population size in each of the aerial survey blocks (C1, C2 and IM) during D2 are provided in Table 3-6. It was not possible to correct for availability bias for turtles because of the lack of aerial survey experimental and field data from turtle studies to use as a standard. The ACF for turtles was therefore set to 1, with a SE of 0 for the Marsh and Sinclair (1989) population estimate method and similarly the probability of availability (Paj) and its SE were set to 1 and 0 respectively for the Pollock et al. (2006) population estimate method. For calculation of the PCF values using the Marsh and Sinclair (1989) method, and for modelling of perception bias in MARK prior to performing Pollock et al. (2006) population estimates, surveys were pooled by block instead of by replicate flight as in previous surveys. D2 surveys were performed with the same observer team for each replicate flight and replicates of each block were flown randomly and not in chronological order. This, in combination with the lack of a third replicate for the C2 block and the similar environmental conditions within each block between replicates, was the reason for pooling D2 surveys in this manner for these calculations. As with previous analyses, group size and its CV were determined on a replicate flight basis. Perception Correction Factors for turtle population size estimations were similar across the blocks and between the port and starboard side in D2, ranging from 1.22 (IM) to 1.70 (C2) (Table 3-6). These results were lower than during the Baseline Phase, but more comparable to other aerial surveys that estimate turtle population sizes in Western Australia (see Preen et al. 1997, PCF range 1.11 to 1.67). During D2, PCFs calculated for turtles were lower compared to surveys completed within the Baseline Phase as a result of increased recaptures between observers (between 21% and 41%; Table 3-7). This is in contrast to the proportion of turtle recaptures recorded during the Baseline Phase which ranged from 2% to 43% (Cardno 2012c). This variation is likely a result of the increased experience of observers during D2 compared to the Baseline Phase. Table 3-6 Details of turtle group size estimates and correction factors used in population estimates for the D2 aerial survey These parameters were used in the Marsh and Sinclair (1989) and Pollock et al. (2006) population estimate methods. Due to a lack of a standard for turtles, the ACF could not be estimated PCF: Perception Correction Factor; all Parameter estimates in this table were based upon all sightings (including those in the inside and outside zones) Survey Block Replicate Mean group size (CV) PCF (CV) Starboard Port (0.03) 1.06 (0.03) 1.15 (0.06) C (0.07) 1.59 (0.08) (0) 1.02 (0.02) 1.04 (0.02) D2 IM 1.22 (0.04) 1.41 (0.07) (0.02) 1.01 (0.01) NA C (0.06) 1.70 (0.11) Prepared for INPEX Cardno 31

42 Table 3-7 Sighting histories for turtles observed during all D2 aerial surveys by individual observers Survey Block Number of turtle seen by: Total # turtles sighted % of turtles sighted by both observers SF SR SB PF PR PB S'board Port C % 24 % D2 IM % 30 % C % 21 % SR: starboard front; SR: starboard rear; SB: starboard both; PF: port front; PR: port rear; PB: port both Population estimates for turtles derived from the Marsh and Sinclair (1989) method at C1, IM and C2 were 792 ± 134 SE, 412 ± 72 SE and 626 ± 127 SE respectively during D2 (Table 3-8). Similarly, Pollock et al. (2006) derived population estimates (±SE) of turtles at C1, IM and C2 were 782 ± 174 SE, 433 ± 103 SE and 720 ± 140 SE respectively during D2 (Table 3-8). Mean turtle population estimates during D2 in C1 and C2 were similar to the mean population estimates calculated during the Baseline Phase (Figure 3-15, Appendix K). In contrast, mean population estimates for turtles at IM were lower, although the difference was not statistically significant during D2 compared to the Baseline Phase (see Section ). Similarities in the population estimates of turtles derived from the Marsh and Sinclair (1989) and Pollock et al. (2006) methods were expected given the similar availability corrections that were applied and the perception bias corrections that were derived by the same family (Lincoln-Petersen) of mark-recapture models. By standardising the availability corrections between population estimation methods, the Pollock et al. (2006) method loses its ability to correct for differential availability of individual sightings due to spatial heterogeneity such as turbidity and sea state. An independent study that could provide an appropriate standard for turtle availability, and therefore enable the calculation of availability corrections for each method, would greatly enhance the accuracy of turtle estimates in the Darwin area. Raw data used for the calculation of population estimates and densities are presented in Appendix L. Table 3-8 Comparison of Turtle population estimates for each block during D2 and the Baseline Phase based on Marsh and Sinclair (1989) and Pollock et al. (2006) methods Baseline Phase D2 Est. Method Block Est. SE Est. SE Marsh and Sinclair C IM C Pollock et al. C IM C Prepared for INPEX Cardno 32

43 a) Marsh and Sinclair Baseline Phase D2 Mean population estimate + SE b) Pollock et al. Baseline Phase D C1 IM C2 Location Figure 3-15 Mean population estimates turtles within each block during D2 and the Baseline Phase based on: a) Marsh and Sinclair (1989); and b) Pollock et al. (2006) population estimate methodologies Prepared for INPEX Cardno 33

44 Turtle Density The mean density of turtles per km 2 ranged between 0.96 ± 0.07 SE to 0.97 ± 0.03 SE at C1 based on Pollock et al. (2006) and Marsh and Sinclair (1989) population estimate methods respectively. Based on Marsh and Sinclair (1989) and Pollock et al. (2006), the mean density (±SE) of turtles per km 2 ranged between 0.36 ± 0.02 SE to 0.38 ± 0.03 SE at IM and 0.61 ± 0.06 SE to 0.71 ± 0.07 SE at C2 respectively. The mean density (±SE) of turtles per km 2 based on raw sightings at C1 was 0.65 ± 0.13 SE, at IM 0.30 ± 0.05 SE and at C ± 0.16 SE during D2. Based on the two population estimate methods, mean turtle densities across all three survey blocks were lower in D2 compared to the Baseline Phase (Figure 3-16, Appendix M). Based on the Marsh and Sinclair (1989) population estimate method there was a significant difference in the mean density of turtles per km 2 among Surveys within the Baseline Phase (p = 0.05) (Table 3-9). Pairwise comparisons were unable to resolve between which Surveys the mean density of turtles per km 2 was significantly different during the Baseline Phase (Table 3-9). The mean density of turtles per km 2 during B2 was 1.23 ± 0.27 SE, which was higher than that recorded during B3 (0.84 ± 0.09 SE) and B1 (0.60 ± 0.09 SE). No significant Phase x Treatment interaction was detected in the density of turtles per km 2 based on the Marsh and Sinclair (1989) and Pollock et al. (2006) population estimate methods. Similarly, there were no significant differences in the mean density of turtles per km 2 between Phases irrespective of Treatment or Treatment irrespective of Phase (Table 3-9) based on these two methods to estimate population size. Based on density estimates derived from raw turtle sightings there was a significant difference in the mean density of turtles per km 2 among Surveys within the Baseline Phase (p = 0.05) (Table 3-9). Pairwise comparisons revealed that the mean density (± SE) of turtle sightings during B3 (0.61 ± 0.07 SE) was significantly higher than during B2 (0.37 ± 0.05 SE) and B1 (0.31 ± 0.04 SE). There was no significant difference in the density per km 2 of turtles based on raw sightings between B1 and B2. The density of turtles per km 2 based on raw sightings differed significantly between Treatments irrespective of Phase (p = 0.04) (Table 3-9). The mean density of turtles was significantly higher at Control locations (0.48 ± 0.05 SE) compared to IM (0.38 ± 0.05 SE). No significant Phase x Treatment interactions or Phase irrespective of Treatment differences were detected in the mean density of turtles per km 2 based on raw sightings (Table 3-9). Prepared for INPEX Cardno 34

45 Table 3-9 Results of univariate PERMANOVA tests for differences in the density of turtles per km based on: a) the Marsh and Sinclair (1989) population estimate method; and b) the Pollock et al. (2006) population estimate method; and c) raw sightings between two Phases (Baseline and Dredging), Phase (B1, B2 and B3 within Baseline Phase and D2 within Dredging Phase), two Treatments (Control and Impact) and three Blocks (C1 and C2 within Control and IM within Impact) ( ) Pooled with those for the Residual/Pooled term in the final analysis ^ No. permutations < 100 so Monte Carlo calculated p-value presented Source of Variation df MS Pseu -F p- (perm) df MS Pseu -F p- (perm) df MS Pseu -F p- (perm) (a) Marsh and Sinclair (b) Pollock et al. (c) Raw sightings Phase ^ ^ <0.01 <0.01 ^0.96 Treatment Phase x Treatment Survey(Phase) > <0.01 Block(Treatment) (1) (0.33) (1.36) 0.26 (1) (0.20) (0.78) 0.39 (1) (0.03) (1.01) 0.33 Phase x Block(Treatment) Treatment x Survey(Phase) Survey(Phase) x Block(Treatment) (1) (0.02) (0.07) 0.78 (1) (<0.01) (0.02) 0.88 (1) (2) (<0.01) (0.02) 0.97 (2) (<0.01) (0.02) 0.98 (2) (2) (0.31) (1.12) 0.34 (2) (0.27) (0.92) 0.41 (2) (0.03) (1.36) 0.26 (<0.01) (0.09) 0.92 (0.02) (1.00) 0.39 Residual/ Pooled Total Pairwise Comparisons (ranked from largest (left) to smallest (right) Baseline: B2 = B1 Baseline: B3 = B1 Baseline: B2 = B1 Baseline: B3 > B1 Baseline: B2 = B3 Baseline: B3 > B2 Treatment: Control > Impact Prepared for INPEX Cardno 35

46 Figure 3-16 Mean turtle density per km 2 (±SE) at each location during D2 and the Baseline Phase based on: a) the Marsh and Sinclair population estimate method; b) the Pollock et al. population estimate method; and c) raw sightings Prepared for INPEX Cardno 36

47 3.2 Land Observations Survey Effort Weather conditions varied between the two land survey locations, with an average BSS of 2 at and 3 at Cullen Bay during D2. During Replicate 1, observations were undertaken on a neap tide with a 2 m tidal difference, with the survey beginning at low tide (Table 3-10). Replicate 2 observations were undertaken on spring tides, beginning on the high tide, with a 5 m tidal difference during the observation period. Raw data for each field day are presented in Appendix O. Table 3-10 Survey effort for land-based observations during D2 Date Location surveyed Survey start time Hours Observing* Tidal window (cm) 20 May : * May 2013 Cullen Bay Rock Wall 07: * May : * May 2013 Cullen Bay Rock Wall 07: * * includes 15 minute off effort period between on effort survey periods Cullen Bay Rock Wall Two turtles were sighted over the two replicate sampling days at the Cullen Bay Rock Wall (Table 3-11). The turtle sighted on the first replicate day was classified as a probable turtle which was observed approximately 50 m from the rock wall (Figure 3-17). The turtle sighted on the second replicate sampling day was observed approximately 30 m from the observation area in a easterly direction and was classified as a probable green turtle (likely a juvenile) (Figure 3-17). No dugongs were sighted during on effort on either observation day. It is noteworthy that a dugong was sighted approximately 200 m from shore at Cullen Bay during an off effort period. The dugong was sighted three times over a 3-minute period, travelling in a north-easterly direction, from Cullen Bay towards Casuarina Beach The number of turtle and dugong sightings at was considerably greater than at Cullen Bay Rock Wall. At, turtles were the prevalent fauna observed, with a 106 sightings recorded (Table 3-11). Sixty-four per cent of turtle sightings were identified as green turtles (62 certain, 6 uncertain). A further 38 (36%) turtle sightings were unable to be identified to species level. The majority (89%) of turtles observed from were considered to be juvenile. The remainder of turtles observed were classified as sub-adults. Three Indo-Pacific humpback dolphins (Sousa chinensis) and one unidentified dolphin were also observed at (Table 3-11, Figure 3-17). Prepared for INPEX Cardno 37

48 Table 3-11 Number of marine mammal and turtle sightings from land survey sites during D2 in May 2013 Cullen Bay Rock Wall Replicate 1 Replicate 2 Sightings Individuals* Sightings Individuals* Dugong Indo-Pacific humpback dolphin Unidentified dolphin Green turtle Unidentified turtle Total sightings Replicate 1 Replicate 2 Sightings Individuals* Sightings Individuals* Dugong Indo-Pacific humpback dolphin Unidentified dolphin Green turtle Unidentified turtle Total sightings Prepared for INPEX Cardno 38

49 Figure 3-17 Distribution of marine mammal and turtle sightings from land-based sites during D2 in May 2013 Prepared for INPEX Cardno 39

50 3.3 Quality Assurance and Quality Control For the aerial survey observer database, there were 282 line entries quality checked with six corrections found (2%). With the Environmental database quality control check, there were 324 line entries checked with 11 errors (3%). During the master database quality check, there were 664 entries checked, with nine corrections (1%). All errors were subsequently corrected. For the land-based survey observer database, 182 line entries were checked and 10 data entry errors were found (6%). All errors were subsequently corrected. Prepared for INPEX Cardno 40

51 4 Discussion The Turtle and Dugong Monitoring Program incorporates various visual survey techniques to estimate and monitor turtle and dugong populations within Darwin Harbour, Hope Inlet, Shoal Bay, Bynoe Harbour, Vernon Islands and across to Melville Island. Current sampling was completed in May 2013, approximately six months after the commencement of CSD operations. Data collected via standardised aerial transects undertaken during D2 has enabled a comparison of turtle and dugong sightings, population estimates and density at three locations - Bynoe Harbour (C1), Darwin Harbour/Hope Inlet (IM) and around the Vernon Islands (C2) - with data collected during the Baseline Phase. The addition of land observations during the current monitoring phase has provided an opportunity to examine the use of alternate observational methods to identify finer-scale turtles and dugong habitat associations within Darwin Harbour. 4.1 Aerial Surveys Dugongs Fewer dugongs were sighted within each location surveyed during D2 (33 individuals in total) compared to the overall average observed throughout the Baseline Phase (average of 88 individuals). The mean numbers of dugongs sighted per replicate flight within each location were lower than those recorded during the Baseline Phase. Based on the Marsh and Sinclair (1989) and Pollock et al. (2006) methods respectively, dugong population estimates for D2 were 99 ± 48 SE and 90 ± 37 SE in IM, and 93 ± 45 SE and 67 ± 26 SE in C2. Due to very few dugong sightings in C1, population estimates could not be calculated for this area in D2. Population estimates for dugongs in D2 were lower than the average recorded in the Baseline Phase for IM (359 ± 147 SE and 231 ± 106 SE) and C2 (227 ± 74 SE and 148 ± 82 SE) based on Marsh and Sinclair (1989) and Pollock et al. (2006) methods, respectively. Dugong population estimates during D2 and throughout the Baseline Phase have been spatially and temporally variable. Such variability is likely to be associated with the inherent behaviour of dugongs (i.e. they are migratory, highly mobile and submerge constantly (Bayliss and Freeland 1989; Marsh et al. 2002)), the conditions experienced during aerial surveys, such as changing sea states and high turbidity, and changes in the distribution of seagrass which they feed on almost exclusively (Lanyon 1991). The number of dugongs in D2 was most comparable to survey B1 in the Baseline Phase which was undertaken at the same time of year (May/June 2012). Temporal variability in the number of dugongs between surveys may be associated with dugong behaviour. Dugong distribution and seagrass mapping provide insight into spatial variability of dugong numbers within surveys and among surveys. Maps for dugong and seagrass distribution in Darwin were produced from data collected during the Baseline Phase and D2 and provided evidence that seagrass, particularly Halophila decipiens, has an important influence on dugong density. Although dugongs have been observed (possibly transiting between foraging areas) throughout the monitoring areas, the greatest densities of dugong sightings in IM during D2 were observed around Shoal Bay and Lee Point. Recent seagrass mapping in May 2013 showed Halophila decipiens was present in those areas; however, this species was only recorded in small areas in other parts of Darwin Harbour (Geo Oceans 2013). In May 2013, seagrass was also recorded to the west of Lee Point but this was Halodule spp., with only small areas of Halophila decipiens. During the Baseline Phase, dugong sightings were associated with mapped seagrass around Fannie Bay and Shoal Bay (Cardno 2012c, Geo Oceans 2012). At this time, although Halodule spp. was present, these areas were dominated by Halophila decipiens. Other studies have shown a close association between Halophila spp dominated seagrass habitats and dugongs within the Moreton Bay region, with dugongs preferring to eat Halophila spp over Halodule spp (Preen 1992). It has been suggested that dugongs actively select seagrass on the basis of nutritional value and Halophila spp has higher nitrogen content and less fibre than other seagrasses (Preen 1992). Prepared for INPEX Cardno 41

52 4.1.2 Turtles Six hundred and twenty-seven turtles were sighted in D2 in comparison to an average of 598 turtles recorded during the Baseline Phase. The mean number of turtle sightings in C1 was higher during D2 compared to the Baseline Phase. In contrast, the mean number of turtle sightings per replicate flight in IM was lower during D2 compared to the Baseline Phase. Turtle sightings in C2 were comparable between D2 and the Baseline Phase. Estimated population sizes based on Marsh and Sinclair (1989) and Pollock et al. (2006) methods were considerably lower in IM during D2 compared to the average population estimate throughout the Baseline Phase. Similarly, although not as evident, population estimates within C1 and C2 were slightly lower during D2 compared to the Baseline Phase. However, considerable variability was evident among the population estimates derived for turtles based on sightings within each location surveyed among survey replicates. The densities of turtles based on raw sightings within Darwin Harbour/Hope Inlet (IM) were lower during D2 compared to the Baseline Phase. However, turtle densities (per km 2 ) based on the two population estimate methods employed (Marsh and Sinclair (1989) and Pollock et al. (2006)) during D2 (0.61 (± 0.06) to 0.71 (± 0.07)) were comparable to those reported in Western Australia (Shark Bay 0.43 per km 2, Preen et al. 1997) and the Torres Strait (2.1 per km 2, Marsh and Lawler 1992), although these densities were considerably less than the results from Ningaloo, where the density of turtles was estimated to be 4.9 per km 2 (Marsh and Lawler 1992). Within Darwin Harbour/Hope Inlet (IM), a decline in the densities of turtle sightings was recorded across 60% of the grid cells in comparison to the Baseline Phase. Inter-survey variation in turtle densities may be a result of short-term movement in and out of specific areas, the pursuit of optimal foraging areas or an influx, for example, of nesting turtles. Within the Darwin Harbour/Hope Inlet area, nesting activities have been monitored at Casuarina Beach since the mid-1990s. Flatback turtles are the most commonly encountered nesting species within the Darwin region with peak nesting periods occurring around September each year (Chatto and Baker 2008). On Bare Sand Island, approximately 50 km to the west of Darwin, nesting flatback turtles have been monitored during peak nesting periods from June to August (M. Guinea 2012, pers. comm.). An increase in the density of turtle sightings was recorded in grid cells within central Darwin Harbour/Hope Inlet (IM), specifically Middle Arm and Wickham Point during D2 compared to a temporally similar period within the Baseline Phase. Such increases in the density of turtles may be associated with the physical characteristics, availability of suitable habitats or foraging activities within these areas. Future TDMP surveys have the potential to provide greater insight into the ongoing use of these areas by turtles within inner Darwin Harbour. The distributions of turtles within each surveyed location were similar during D2 compared with the Baseline Phase. Turtle sightings to date have most frequently been recorded within relatively shallow water, but given there is limited information about habitat types in the survey locations it is difficult to interpret whether turtles prefer particular habitats over others. Where benthic habitats have been identified, turtles were sighted over reef, sand and seagrass. Known foraging habitats of green turtles include coral and rocky reefs, and inshore areas that support algae and/or seagrass (Whiting 2000; Limpus 2008). It is unclear whether the turtles sighted over particular habitats were travelling or foraging. 4.2 Land Observations During May 2013, land observations were introduced as a replacement to boat-based surveys to provide additional information on finer-scale behaviour, habitat use and species identification of turtles and dugongs around Darwin Harbour. During boat surveys conducted in October 2012, approximately 65% of turtles were unable to be identified to species level. Land-based observations at recognised hotspots, including Island and Cullen Bay, have increased the capability of the monitoring program in addressing the objectives of the TDMP, with only 34% of turtles remaining unidentified in the current survey. No statistical comparisons were undertaken on land data collected during D2 due to insufficient data. During the survey period, observation counts at Cullen Bay were small, with two turtle sightings during on effort sampling. The general location of these turtles was over what was assumed to be sandy bottom, near a small patch of seagrass that had been previously mapped (Geo Oceans 2012). However, it is evident that seagrass distribution varies considerably in the Darwin area (e.g. Geo Oceans 2012, 2013), so it is highly probable that it has changed in these areas and may be one of the reasons as to the lack of sightings in this Prepared for INPEX Cardno 42

53 area. During an off effort period at Cullen Bay, a single dugong was also observed close to a highconfidence seagrass habitat (Geo Oceans 2013). Although sighting counts of turtles and dugongs around Cullen Bay were low, local experts identified this as a potential hotspot. The small number of sightings may either be due to environmental conditions during survey periods or a small number of animals available in the area for observation on the given days. Higher winds, increased sea state and wave action may have reduced the ability of observers to observe turtles. This was particularly evident during Replicate 1 at Cullen Bay, where average sea state was 3. Lower winds and more optimal conditions on the second day were recorded; however, this did not increase the sightings in the area. After only two replicates of the area, it was unclear whether this result is a reflection of a lower number of species utilising this habitat as a whole, or purely a result of the animals available in the area on the given days. In contrast to Cullen Bay, there were no sightings of dugongs at Island, but observations of turtles were considerably higher, with over 100 turtle sightings over the two day period. Of these, 64% were confirmed as green turtles and an estimated 89% of the total sightings were recorded as juveniles. Previous studies have recorded large numbers of turtles around Island suggesting that it is an important habitat for green turtles and may indicate an important foraging ground (Cardno 2012c, 2013; Whiting 2004). In the Northern Territory, green turtles have been recorded nesting in bioregions across the north and the east of the Top End, on islands and mainland beaches (Chatto and Baker 2008). Immature green turtles are year-round foraging residents to specific regions, where they feed in coastal waters and are almost totally herbivorous, feeding principally on seagrass, algae and mangrove fruits (Limpus 2008). After a number of years in the open ocean juvenile turtles, with a carapace length of between 40 cm and 50 cm, recruit to shallow water habitats where they occupy distinct home ranges as they feed and grow to maturity (Makowski et al. 2006). Juvenile turtles may remain in these areas for extended periods, possibly decades (Limpus and Chaloupka 1997). A recent study of a satellite tagged juvenile green turtle at Island depicted minimal movement patterns over a period of two months, with high-accuracy GPS positions indicating a maximum movement of only 600 m from the capture location (Cardno 2013). It is most probable that green turtles, as well as many of the individuals that were not identified at this site, are resident animals, and will remain in the area for many years. During land observations at, two turtles were individually identified due to recognisable markings on their heads and/or carapace. An indication of turtle dive time durations were able to be obtained by monitoring these individuals. One juvenile green turtle was identified on the southern side of the bridge, surfacing three times within the space of two minutes at a maximum distance of 60 m from the observer. Another juvenile green turtle (approximately 35 cm Curved Carapace Length (CCL)) was observed surfacing at a maximum distance of 15 m away from the observer on the northern side of the bridge with dive durations of approximately 10 minutes over a 50-minute period. During these dives the juvenile turtle may have been foraging on the nearby reef habitat. The dive times of this second juvenile green turtle were similar to the dive duration of green turtles off Heron Island in Queensland where their dive duration was measured to be 13.1 minutes (± 1.2) (Southward et al. 2003). Tidal variation at Island may also have influenced the number of turtles observed in the area. Larger counts of turtles were recorded during the neap tide (n = 70) than the spring tide (n = 45). Although the spring tide increases the available areas for turtles and other species for foraging, during the extreme high tide (maximum of approximately 7.5 m), no turtles were recorded. It is probable that in extreme spring tides, tidal currents within the channel are too strong for turtles to swim against (BSS 3 on the northern side of the bridge during the outgoing tide). It is feasible that turtles swim with the outgoing tide into the northern and southern channels where currents are likely to be slower and wait until the tide settles as a means of conserving energy. Observations from the boat during turtle netting surveys noted similar behaviour, with turtles moving into the deeper channels to the north and south on the outgoing tide (Cardno 2012c). This would be an adaptive strategy for smaller animals, such as turtles, to conserve energy. Higher abundance of turtles were not recorded until at least two hours before the low tide (between 3.16 m and 2.16 m) where the tide had dropped 4 m from the time that observations had begun and the current appeared to have slowed. Ongoing land-based observations will likely enable a greater understanding of fine-scale behaviour of dugong and turtle species within the locations studied. Prepared for INPEX Cardno 43

54 It is recognised that Island provides important habitat and foraging grounds for turtles, and possibly also for dugongs and inshore delphinids. Land observations at this site were successful, with large numbers of turtle sightings recorded in this area. Reef and foraging grounds extend below the observation platform (bridge) bringing turtles closer to observers and increasing the potential for observers to detect and identify turtle species. Information recorded at this land observation site provides useful data on finer-scale behaviour of turtles and meets the second objective of the TDMP. Prepared for INPEX Cardno 44

55 5 Conclusions It is important to gain a comprehensive understanding of abundance, density and distribution of turtles and dugongs in Darwin Harbour and surrounding nearshore waters, in order to monitor these species adequately temporally, spatially and during potential disturbance. Aerial surveys were appropriate for the collection of data on a broader spatial scale to meet the objectives of the TDMP. Aerial surveys in D2 (May 2013) for the TDMP resulted in only a small number of dugongs sighted, with some areas recordings less than five individuals. This restricted the calculation of population estimates for some flight replicates. Differences in dugong and turtle distribution during surveys to date suggest that movement patterns may be dictated by a number of variables, including seasonal movements relating to water temperature, local tidal influences or changes in seagrass distribution. It is possible that dugongs and turtles change their patterns of movement in search of foraging areas and may vary with fluctuations in seagrass distribution. Nonetheless, statistical analyses revealed no significant differences in the mean density of dugongs between C1/C2 and IM between D2 and the Baseline Phase. The mean density of turtles was significantly higher in C1/C2 compared to IM; however, this was consistent between D2 and the Baseline Phase. The calculations of regional relative densities for both turtles and dugongs was used in identifying potential hotspots around the Darwin Harbour and surrounding waters and changes over time. Correlation of results from the Seagrass Monitoring Program with turtle and dugong distribution and densities over time assists identification of these potential sites within the survey locations. It was evident through the Baseline Phase of the monitoring program that, although aerial surveys provide adequate data in assessing population distribution and abundance, it was not possible to distinguish turtle species. Boat-based observations used in the Baseline Phase surveys were unable to distinguish turtle species and, therefore, land observations were introduced at recognised hotspots around Darwin Harbour; Cullen Bay and Island. Observations of turtles at Island provided useful data on species identification and dive durations and confirmed the importance of this area as a critical habitat for resident turtles in Darwin Harbour. Prepared for INPEX Cardno 45

56 6 Acknowledgements This report was written by Dr Michelle Blewitt, Megan Rice and Dr Lachlan Barnes and reviewed by Dr Craig Blount and Joanna Lamb. Fieldwork was undertaken by Megan Rice, Dr Glenn Dunshea, Dr Susan Gibbs, Barry Krueger, Paul Tod and Dr Michelle Blewitt. GIS support was provided by Liz Fulton and the Wollongong Cardno office. Data analysis was undertaken by Dr Glenn Dunshea, Megan Rice, Dr Lachlan Barnes and Dr Michelle Blewitt. The figures, tables and appendices were prepared by Megan Rice, Dr Michelle Blewitt and Dr Glenn Dunshea. The TDMP was reviewed by Professor Helene Marsh from James Cook University. The authors would like to thank the Ichthys Project Dredging Expert Panel (IPDEP) members for constructive criticism throughout the ongoing monitoring program. Prepared for INPEX Cardno 46

57 7 References Anderson, M.J. (2001). A new method for non-parametric multivariate analysis of variance. Austral Ecology 26, pp Bayliss, P. and Freeland, W.J. (1989). Seasonal distribution and abundance of dugongs in the Western Gulf of Carpentaria. Australian Wildlife Research 16, pp Cardno (2012c). Turtle and Dugong Monitoring Program Baseline Report.. Prepared for INPEX. November 2012, pp Cardno (2012d). Nearshore Environmental Monitoring Plan. Prepared for INPEX August Cardno (2013). Routine Turtle and Dugong Monitoring Program Report Dredging Report 1. Ichthys Nearshore Environmental Monitoring Program. Prepared for INPEX, January 2013, pp Chatto, R. and Baker, B. (2008). The Distribution and Status of Marine Turtle Nesting in the Northern Territory. Technical Report 77. Parks and Wildlife Service, Department of Natural Resources, Environment, The Arts and Sport. Geo Oceans (2012). : Seagrass Habitat Monitoring Survey, October Technical Report. Prepared for Cardno on behalf of INPEX, November Geo Oceans (2013). : Seagrass Habitat Monitoring Survey, May Technical Report. Prepared for Cardno on behalf of INPEX, June Hodgson, A., Marsh, H., Marsh, L., Grech, A., McMahon, A. and Parra, G. (2011). Dugong Aerial Survey Manual. James Cook University, Townsville. INPEX (2012). Dredging and Spoil Disposal Management Plan. pp Lanyon, J.M. (1991). The nutritional ecology of the dugong (Dugong dugon) in tropical north Queensland. Ph.D. Thesis, Monash University, Melbourne. Limpus, C.J (2008). Green turtle, Chelonia mydas (Linnaeus). In: A Biological Review of Australian Marine Turtles. Queensland Government Environmental Protection Agency. Limpus, C.J. and Chaloupka, M. (1997). Nonparametric regression modelling of green sea turtle growth rates (southern Great Barrier Reef). Marine Ecology Progress Series 149, pp Makowski, C., Seminoff, J.A. and Salmon, M. (2006). Home range and habitat use of juvenile Atlantic green turtles (Chelonia mydas L.) on shallow reef habitats in Palm Beach, Florida, USA. Marine Biology. 148, pp Marsh, H. and Lawler, I. (1992). The Status of Dugongs, Sea Turtles and Dolphins in the Torres Strait Region. Report to The Australian Fish Management Authority. June Marsh, H. and Sinclair, D.F. (1989). Correcting for visibility bias in strip transect aerial surveys of aquatic fauna. Journal of Wildlife Management 53, pp Marsh, H., Penrose, H., Eros, C. and Hughes, J. (2002). Dugong: status reports and action plans for countries and territories in its range. Cambridge, UK: IUCN. Pollock, K., Marsh, H., Lawler, I. R. and Alldredge, M.W. (2006). Estimating animal abundance in heterogeneous environments: an application to aerial surveys for dugongs. Journal of Wildlife Management 70: Preen, A.R. (1992). Interactions between dugongs and seagrasses in a sub-tropical environment. Ph.D. Thesis. James Cook University, Townsville. Preen, A. (1995). Impacts of dugong foraging on seagrass habitats: observational and experimental evidence for cultivation grazing. Marine Ecology Progress Series 124, pp Preen A.R., Marsh, H., Lawler, I.R., Prince, R.I.T. and Shepherd, R. (1997). Distribution and abundance of dugongs, turtles, dolphins and other megafauna in Shark Bay, Ningaloo Reef and Exmouth Gulf, Western Australia. Wildlife Research 24, pp Whiting, S.D. (2000). The ecology of immature green and hawksbill turtles foraging on two reef systems in northern Australia. Ph.D. Thesis. Northern Territory University, Darwin. Whiting, S.D. (2004). Conserving dugongs in Darwin Harbour. Report to Natural Heritage Trust, Coast and Clean Seas Project, # Prepared for INPEX Cardno 47

58 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Ichthys Nearshore Environmental Monitoring Program APPENDIX A SUMMARY OF AERIAL SURVEY EFFORT DURING BASELINE AND DREDGING PHASE SURVEYS Prepared for INPEX Cardno 2

59 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Appendix A: Summary of aerial survey effort for each block (C1, IM and C2) during Baseline and Dredging Phase surveys Bynoe Harbour (C1) Darwin Harbour (IM) Vernon Islands (C2) Baseline Survey Period B1 B2 B3 D2 B1 B2 B3 D2 B1 B2 B3 D2 Number of transects Total length transects (km) Total sampled area (km²) Overall surveyed area (km²) Proportion surveyed* (%) Average survey duration (h: min: sec) :54:17 1:23:23 1:27:53 1:06:32 1:25:47 1:25:36 1:26:55 1:36:53 1:36:17 1:12:08 1:20:36 1:15:09 *The proportion of surveyed area is averaged in the calculation of total area surveyed. B1 = 2 replicates, B2 and B3 = 3 replicates; D2 = 2/3 replicates. Prepared for INPEX Cardno 52

60 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Ichthys Nearshore Environmental Monitoring Program APPENDIX B TIDAL RANGES AND DUGONG DENSITIES FOR DREDGING AND BASELINE PHASE AERIAL SURVEYS Prepared for INPEX Cardno

61 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Appendix B: Summary of dugong densities and tidal ranges recorded within the IM (Darwin Harbour) block for D2 and Baseline Phase aerial surveys (B1, B2 and B3). Within each tidal area (1-8), tidal ranges (cm) were calculated according to flight time. Densities (number/km2) were calculated on the area of water sampled within each grid cell. Baseline Phase Tidal Area Grid cell B1 B2 B3 D2 Tidal Range Tidal Range Tidal Range Tidal Range Rep 1 Rep 2 Density Rep 1 Rep 2 Rep 3 Density Rep 1 Rep 2 Rep 3 Density Rep 1 Rep 2 Rep 3 Density Prepared for INPEX Cardno 54

62 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Baseline Phase Tidal Area Grid cell B1 B2 B3 D2 Tidal Range Tidal Range Tidal Range Tidal Range Rep 1 Rep 2 Density Rep 1 Rep 2 Rep 3 Density Rep 1 Rep 2 Rep 3 Density Rep 1 Rep 2 Rep 3 Density Prepared for INPEX Cardno 55

63 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Ichthys Nearshore Environmental Monitoring Program APPENDIX C SUMMARY OF DUGONG SIGHTINGS ACROSS DREDGING AND BASELINE PHASE SURVEYS Prepared for INPEX Cardno

64 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Appendix C: Summary of the number of dugongs recorded during Dredging and Baseline Phase Surveys. All areas Total Survey period D2 B1 B2 B3 Replication number R1 R2 R3 Total Number of observations Number of animals Number of calves Maximum group size Bynoe Harbour (C1) Total Survey period D2 B1 B2 B3 Replication number R1 R2 R3 Total Number of observations Number of animals Number of calves Maximum group size Darwin Harbour (IM) Total Survey period D2 B1 B2 B3 Replication number R1 R2 R3 Total Number of observations Number of animals Number of calves Maximum group size Vernon Islands (C2) Total Survey period D2 B1 B2 B3 Replication number R1 R2 R3 Total Number of observations 2 6 * Number of animals 3 8 * Number of calves 0 0 * Maximum group size 2 3 * *No Flight undertaken due to weather; R= replicate Prepared for INPEX Cardno 56

65 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Ichthys Nearshore Environmental Monitoring Program APPENDIX D DUGONG REGIONAL RELATIVE DENSITIES DURING BASELINE PHASE SURVEYS Prepared for INPEX Cardno

66 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Prepared for INPEX Cardno 57

67 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Prepared for INPEX Cardno 58

68 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Prepared for INPEX Cardno 59

69 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Ichthys Nearshore Environmental Monitoring Program APPENDIX E DISTRIBUTION OF DUGONGS AND TURTLES RECORDED ACROSS IM BLOCK DURING DREDGING AND BASELINE PHASE SURVEYS Prepared for INPEX Cardno

70 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Appendix E: Distribution of dugongs and turtles in Darwin Harbour (IM), overlaid with confirmed seagrass habitat (seagrass data: Geo Oceans 2013). Note B2 sightings data have not been overlaid on seagrass maps as no seagrass mapping was undertaken during this period Prepared for INPEX Cardno 60

71 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Ichthys Nearshore Environmental Monitoring Program APPENDIX F DUGONG POPULATION SIZE ESTIMATES DURING DREDGING AND BASELINE PHASE SURVEYS Prepared for INPEX Cardno 61

72 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Appendix F: Comparison of dugong population size estimates (± SE) during Dredging (D2) and Baseline Phase surveys (B1, B2 and B3) Marsh and Sinclair Pollock et al. Block Month Replicate Est. SE Est. SE C1 C2 IM June (B1) July (B2) Sep/Oct (B3) May (D2) June (B1) July (B2) Sep/Oct (B3) May (D2) June (B1) July (B2) Sep/Oct (B3) May (D2) Prepared for INPEX Cardno 62

73 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Ichthys Nearshore Environmental Monitoring Program APPENDIX G CORRECTED DUGONG DENSITIES DURING DREDGING AND BASELINE PHASE SURVEYS Prepared for INPEX Cardno 63

74 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Appendix G: Dugong density (± CI) for blocks C1, C2 and IM during Dredging (D2) and Baseline Phase surveys (B1, B2 and B3 using the Marsh and Sinclair (1989a) method Marsh and Sinclair Pollock et al. Block Month Replicate Est. SE Est. SE C1 C2 IM June (B1) July (B2) Sep/Oct (B3) May (D2) June (B1) July (B2) Sep/Oct (B3) May (D2) June (B1) July (B2) Sep/Oct (B3) May (D2) Prepared for INPEX Cardno 64

75 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Ichthys Nearshore Environmental Monitoring Program APPENDIX H DUGONG GROUP SIZE DATA FOR POPULATION ESTIMATE CALCULATIONS Prepared for INPEX Cardno

76 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Appendix H: Raw Data for Calculating Dugong Population Size in Aerial Surveys *Note this is not all groups - only groups in transect (i.e. not including sightings on the outside or inside zones) Aerial Survey - Dugong Group Sightings Data Survey Block Replicate Transect Total Length Total Area Port groups Stbd Groups D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control Prepared for INPEX Cardno 65

77 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Aerial Survey - Dugong Group Sightings Data Survey Block Replicate Transect Total Length Total Area Port groups Stbd Groups D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control Prepared for INPEX Cardno 66

78 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Aerial Survey - Dugong Group Sightings Data Survey Block Replicate Transect Total Length Total Area Port groups Stbd Groups D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact Prepared for INPEX Cardno 67

79 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Aerial Survey - Dugong Group Sightings Data Survey Block Replicate Transect Total Length Total Area Port groups Stbd Groups D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact Prepared for INPEX Cardno 68

80 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Aerial Survey - Dugong Group Sightings Data Survey Block Replicate Transect Total Length Total Area Port groups Stbd Groups D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Impact D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control Prepared for INPEX Cardno 69

81 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Aerial Survey - Dugong Group Sightings Data Survey Block Replicate Transect Total Length Total Area Port groups Stbd Groups D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control Prepared for INPEX Cardno 70

82 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Aerial Survey - Dugong Group Sightings Data Survey Block Replicate Transect Total Length Total Area Port groups Stbd Groups D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Control D2 Impact 1 29a D2 Impact 2 29a D2 Impact 3 29a D2 Impact 1 29b D2 Impact 2 29b D2 Impact 3 29b D2 Impact 1 30a D2 Impact 2 30a D2 Impact 3 30a D2 Impact 1 30b D2 Impact 2 30b D2 Impact 3 30b D2 Impact 1 31a D2 Impact 2 31a D2 Impact 3 31a D2 Impact 1 31b D2 Impact 2 31b D2 Impact 3 31b D2 Impact 1 32a Prepared for INPEX Cardno 71

83 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Aerial Survey - Dugong Group Sightings Data Survey Block Replicate Transect Total Length Total Area Port groups Stbd Groups D2 Impact 2 32a D2 Impact 3 32a D2 Impact 1 32b D2 Impact 2 32b D2 Impact 3 32b Prepared for INPEX Cardno 72

84 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Ichthys Nearshore Environmental Monitoring Program APPENDIX I SUMMARY OF TURTLE SIGHTINGS ACROSS DREDGING AND BASELINE PHASE SURVEYS Prepared for INPEX Cardno

85 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Appendix I: Summary of the number of turtles recorded during Dredging and Baseline Phase Surveys All Areas Total Survey period D2 B1 B2 B3 Replication number R1 R2 R3 Total Number of observations Number of animals Maximum group size Bynoe Harbour (C1) Total Survey period D2 B1 B2 B3 Replication number R1 R2 R3 Total Number of observations Number of animals Maximum group size Darwin Harbour (IM) Total Survey period D2 B1 B2 B3 Replication number R1 R2 R3 Total Number of observations Number of animals Maximum group size Vernon Islands (C2) Total Survey period D2 B1 B2 B3 Replication number R1 R2 R3 Total Number of observations * Number of animals * Maximum group size 2 2 * *No flight due to weather; R=replicate. Prepared for INPEX Cardno 73

86 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Ichthys Nearshore Environmental Monitoring Program APPENDIX J DUGONG REGIONAL RELATIVE DENSITITES DURING BASELINE PHASE SURVEYS Prepared for INPEX Cardno

87 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Prepared for INPEX Cardno 74

88 Routine Turtle and Dugong Monitoring Program Report- Dredging Report 2 Prepared for INPEX Cardno 75