Marine Turtle Nesting Populations: Avoid Island Flatback Turtles, breeding season

Transcription

1 1 Marine Turtle Nesting Populations: Avoid Island Flatback Turtles, breeding season Nancy N. FITZSIMMONS and Colin J. LIMPUS DEPARTMENT OF ENVIRONMENT AND HERITAGE PROTECTION, QUEENSLAND TRUST FOR NATURE

2 Cover photographs: Scenes from the census of nesting flatback turtles, Natator depressus, at Avoid Island, November March Photos by Nancy FitzSimmons and Aly Ross. This report should be cited as: Nancy N. FITZSIMMONS and Colin J. LIMPUS (2015). Marine Turtle Nesting Populations: Avoid Island Flatback Turtles, breeding season. Queensland Government. Report produced for the Ecosystem Research and Monitoring Program Advisory Panel as part of Gladstone Ports Corporation Ecosystem Research and Monitoring Program. 19 pp. This report has been produced for the Ecosystem Research and Monitoring Program Advisory Panel as part of Gladstone Ports Corporation Ecosystem Research and Monitoring Program. The study was undertaken under a Consultancy Agreement (CA ) between Gladstone Ports Corporation and the Department of Environment and heritage Protection to monitor marine turtle nesting at Peak Island and Avoid Island. This publication has been compiled by the Queensland Department of Environment and Heritage Protection (EHP). Gladstone Ports Corporation Disclaimer: Except as permitted by the Copyright Act 1968, no part of the work may in any form or by any electronic, mechanical, photocopying, recording, or any other means be reproduced, stored in a retrieval system or be broadcast or transmitted without prior written permission of Gladstone Ports Corporation and/or the Ecosystem Research and Monitoring Program Advisory Panel. This document has been prepared with all due diligence and care, based on the best available information at the time of publication, without peer review, and the information contained herein is subject to change without notice. The copyright owner shall not be liable for technical or other errors or omissions contained within the document. The reader/user accepts all risks and responsibility for losses, damages, costs and other consequences resulting directly or indirectly from using this information. Any decisions made by other parties based on this document are solely the responsibility of those parties. Information contained in this document is from a number of sources and, as such, does not necessarily represent the policies of GPC or the government/departmental. Enquiries about reproduction, including downloading or printing the web version, should be directed to ermp@gpcl.com.au 2

3 MARINE TURTLE NESTING POPULATIONS: AVOID ISLAND FLATBACK TURTLES, BREEDING SEASON Colin J. LIMPUS and Nancy N. FITZSIMMONS EXECUTIVE SUMMARY This report summarises the results of monitoring the eastern Australian flatback turtle nesting population at a representative index beach towards the northern extent of the population s nesting range during the breeding season. A total of 68 individual flatback turtles were identified during the two-week census period from 23 November 06 December There were 95 nesting crawls and a total of 72 clutches laid. This is only the fourth season that census data have been collected, so meaningful trend analyses are not possible. As observed at other nesting beaches, the eastern Australian nesting flatback turtles at Avoid Island display a high fidelity to the island, with all remigrant turtles having been tagged previously at Avoid Island or Wild Duck Island. These turtles display normal demographic features for the eastern Australian flatback turtle stock: o Nesting females had a mean curved carapace length = 93.2 cm, and in marked nests there were, on average, 51 eggs per clutch. No turtles were observed to lay a successive clutch within the 14-day census period. Beach erosion from Cyclone Dylan in late January 2014 was still apparent, although the beach profile had filled in substantially. Cyclone Marcia on 19 February 2015 would have caused the loss of several flatback turtle clutches laid below the dunes after the first week of December. A post-cyclone survey was not conducted Reliable estimates of hatching success and hatchling emergence success were compromised by having to evacuate the island due to Cyclone Marcia half way through the trip. However, we were able to get data on 48 marked nests and an additional 14 nests that were dug up while searching for marked nests or were outside of the census period. The 48 marked nests had an average hatch success and hatchling emergence success of 86.4%. Existing management at Avoid Island is providing important protected habitat for the eastern Australian nesting population of flatback turtles in an area free of large terrestrial predators such as pigs, dogs, foxes and goannas. 3

4 MARINE TURTLE NESTING POPULATIONS: AVOID ISLAND FLATBACK TURTLES, BREEDING SEASON INTRODUCTION This report has been produced for the Ecosystem Research and Monitoring Program Advisory Panel (ERMPAP) as part of Gladstone Ports Corporation s Ecosystem Research and Monitoring Program. The study was undertaken under a Consultancy Agreement (CA130032) between the Gladstone Ports Corporation ERMPAP and the Department of Environment and Heritage Protection to monitor marine turtle nesting populations on Peak Island and Avoid Island. This report provides a summary of results from monitoring marine turtle nesting at Avoid Island during the breeding season, the second year of study under this contract and the forth year that the population has been monitored. Avoid Island, o S, o E, is a continental island located just north of Broad Sound, lying approximately 18 km from the nearest mainland shore and approximately 125 km southeast of the city of Mackay on the mainland coast of eastern Australia (Figure 1a). The island is owned by the Queensland Trust for Nature (QTFN), which manages the island as a nature refuge. Avoid Island sits within a Habitat Protection Zone of the Great Barrier Reef Coast Marine Park and the Great Barrier Reef Marine Park. The island is closed to visitation by the general public and is uninhabited except by the turtle monitoring team during annual monitoring visits, and periodic visits by QTFN personnel for maintenance. As a consequence, the turtle nesting habitat of Avoid Island and the immediately adjacent inter-nesting habitat are managed to provide a high level of habitat protection to the nesting turtle population. There is a house, built in the 1970s, on the highest point on the island, and a shed. There are tracks that circle the island and a grass airstrip, which are maintained with a tractor mower. For the turtle monitoring, QTFN built four large tent platforms and erected four tents for the turtle research team and did maintenance on the house. The Island is approximately 1.6 km long and 0.4 km wide, and has undulating terrain with a rise on the northern end of the island. There are three main nesting beaches (South Beach, Middle Beach, North Beach) on the eastern side of the island that are bordered by rocky outcrops and each beach is fronted by tidal sandy mud flats with scattered rocky shelves (Figure 1b). These beaches are backed by dunes, providing nesting habitat on the beach slope and top of the dunes, particularly at South Beach. Other beaches on the island are either too narrow or rocky to provide suitable nesting habitat, though occasional nesting occurs on West Beach, the largest westerly facing beach (Jones and Venz, 2008, Kevin English, pers. comm.). Avoid Island appears to support a moderate density of nesting flatback turtles in the East Australian (EA) stock (Limpus et al. 2013) and has been selected as an index beach for long term monitoring of flatback turtles within the EA stock. An initial census of the Avoid Island flatback turtle nesting population was conducted during the breeding season (Jones and Venz 2008) and annual monitoring commenced in the breeding season (FitzSimmons, 2013; FitzSimmons and Limpus 2014) 4

5 METHODOLOGY Standard Queensland Turtle Conservation Project methodologies (Limpus et al., 1983; Limpus, 1985) were followed to monitor nesting females and their clutches. Nesting females Three beaches were monitored nightly from 23 November - 06 December 2014 in conjunction with students from a conservation biology class run through the University of New South Wales. We used two teams of three students and one-two experienced people to monitor the A3 (south) and A2 (middle) beaches and a third team to monitor the A1 (north) beach. Additional monitoring occurred from 7 10 December 2014 by experienced people, accompanied by students from the North Mackay and Sarina high schools during 9-10 December. Nightly monitoring began at least two hours before low tide and continued for about four hours after low tide, depending on if turtles were still active on the beach. Procedures included: Each turtle left the beach with a minimum of two titanium tags (manufactured by Stockbrands Australia) in the front left and right flipper tagging positions (Limpus, 1992), generally proximal to the flipper scute closest to the body. If scar tissue from previous tagging made this position unsuitable for tagging, tags were applied distally to this last scute. Passive Integrated Transponder (PIT) tags were injected into the upper left (or occasionally right) shoulder (just below the carapace) of nesting females. PIT tags were manufactured by Animal Electronic I.D. Systems. Curved carapace length (CCL ± 0.1 cm) was measured from the skin/carapace junction at the anterior edge of the nuchal scale, along the midline, to the posterior junction of the end post-vertebral scutes at the rear of the carapace using a flexible fibreglass tape measure. This was done multiple times by students and checked against the measurements of an experienced person. Any barnacles living along the midline of the carapace were removed prior to measuring. Any damage to the turtle or unusual features were recorded. If egg laying was observed, a nest tag (fluoro flagging tape approximately 20cm long) was placed in the nest. On the nest tags, the date of laying and a tag number of the turtle was written using a no-water-soluble ballpoint pen. The nest tag enabled identification of individual clutches of eggs when excavated following hatchling emergence some two months later. Nest locations were recorded using a hand held GPS (global positioning system) unit (± 4 m) and measurements (± 1 cm) were taken to at least two nearby trees or shrubs using a 30 m tape measure and a map drawn for reference. Habitat type of the nest location was recorded. Emergence Success A second trip to Avoid Island to determine emergence and incubation success for the previously marked nests, was started on 16 February 2015 but the trip was cut short on 18 February due to Tropical Cyclone Marcia approaching. Nest locations were determined using GPS locations and nest maps and confirmed by the presence of nest tags. 5

6 A clutch was assessed for incubation success and hatchling emergence success by excavating the nest, usually 24 hr after the hatchlings had left the nest. A count is made of hatched eggs, unhatched eggs with embryos, unhatched eggs with no signs of embryonic development (= undeveloped egg), eggs showing signs of predation by crabs or other animals (= predated egg), live hatchlings trapped in the nest, and dead hatchling within the nest. The number of hatched eggs was determined by the number of eggshell fragments that were larger than 50% of that expected from an entire egg. Estimated clutch count = hatched eggs + unhatched eggs + undeveloped eggs + predated eggs Hatching success = (hatched eggs estimated clutch count)*100 %; Emergence success = (hatched eggs [live + dead hatchlings] estimated clutch count)*100 %. The depth to the bottom of the egg chamber was measured (+ 5 mm) and observations on the nest environment were made, such as erosion and water inundation. Sand Temperature Monitoring Two sand temperature data loggers had been placed on site during the breeding season in representative nesting environments at a depth of 50 cm to monitor an open and a shaded nesting location. The temperature logger, which had been placed in the shady location on the upper beach slope, was washed away by Cyclone Dylan, subsequently found amongst beach debris and relocated onto higher ground on the first dune. Data from these data loggers was downloaded in 18 February 2015 and the loggers were replaced in situ to continue recording. Their locations are: shade logger at o S; o E5 and sun logger at o S o E. RESULTS Tagging Census A total of 68 individual flatback turtles engaged in nesting activities were identified during the two-week census period, 23 November 06 December 2014 (Table 1). One additional turtle was identified from December and six other turtles observed in that time period had been encountered during the census. No other species of turtle was recorded as nesting during this period. All data discussed below are restricted to the census data unless otherwise noted. During the season, no flatback turtle was recorded with tags that had been recorded nesting at any beach other than Avoid Island, although in the season year, one turtle was recorded that had been tagged originally at Wild Duck Island in It is too early in the study to accurately estimate the recruitment rate of first time breeding females into the adult nesting population, as measured by the proportion of first time tagged nesting females. As expected, this value has declined from 78.2% in (FitzSimmons 2013) to 66.7% in (FitzSimmons and Limpus 2014) and 50.0% in

7 The mean nightly number of turtles coming ashore for nesting (track count) was 6.8 (SD = 3.8, n = 14, range = Table 2, Figure 2). The mean number of clutches laid per night was 5.1 (SD = 2.7, n = 14, range = 0-10). There were 95 recorded flatback turtle nesting crawls during the census period. Ten additional nesting crawls occurred from December. Most nesting activity occurred on South Beach (A3), which is the largest beach (Figure 3). Nesting success, the proportion of nesting crawls that resulted in eggs being laid by the turtle, was 75.8% for the island during the census period, which is higher than last season (59.8%). Nesting success was 81.2% at North Beach (n = 11) and 74.4 % at South Beach (n = 82). Only two turtles nested on Middle Beach, both of which laid eggs. For three missed turtles it could not be determined whether or not they had nested. The mean return interval for a turtle returning to attempt to lay eggs following an unsuccessful nesting attempt was 1.4 days (SD = 0.8, n = 9, range = 0-3 days). One turtle did not nest until her third emergence, all returning turtles successfully nested. Eleven turtles were observed during a second nesting attempt. Of these 11 turtles, 10 had known dates of egg laying. Nine of the turtles had a re-nesting interval of 13 days, the remaining turtle nesting again after 12 days. The observed second nests of six of the turtles occurred outside of the census period on 9 and 10 December Size of nesting females The mean size of the nesting female flatback turtles was CCL = 93.2 cm (SD = 2.8, n = 67, range = ; Table 3, Figure 4). The mean CCL of primary tagged turtles, which includes first time breeding females and previously untagged remigrants, was 2.1 cm less than that of remigrant turtles. It is not possible to assess whether there is a difference in the size of actual first time versus remigrant breeders until more of the turtles are tagged. Remigration Remigration interval, the number of years between recorded breeding seasons, for adult female flatback turtles at Avoid Island during the 23 November 6 December 2014 census period can be assessed for turtles that were observed in the two pervious breeding seasons. This included 24 turtles observed in 2012 and four turtles from 2013 to give a mean remigration interval of 1.9 years (Table 3). Additionally, 10 remigrant turtles were originally tagged in 2007 at Avoid Island, four of which nested in Nesting, incubation success and hatchlings The first clutch observed producing hatchlings occurred on 06 December Only one other clutch emergence was observed after the census period on 9 December A total of 72 clutches were laid during the two-week census and all of these were marked for determining emergence success (Table 2). The field trip to document emergence and hatch success started on 16 February 2015 but was cut short by the threat of Tropical Cyclone Marcia, and the team was evacuated on 18 February A total of 48 marked nests were found in the limited time period in addition to 4 nests laid outside of the census period, eight nests that were found after 7

8 observing hatchling tracks and 10 nests found while digging for marked nests, some of which could have been marked nests but without the nest tag in place. The average number of eggs in census nests was 50.8 counted after hatchling emergence, and both hatching success and emergence success were 86.4%, as no live or dead hatchlings were found in the 48 nests (Table 4). If the 14 nests that were found either accidentally, or outside of the census period are included in the calculations there is little change in the data (51 eggs, 85% success). The eight nests found by observing hatchling tracks had higher success ratios of 92%, which is expected, given that nests with poor or no success have a reduced probability of being observed. There were no observations of incubating clutches having been dug into by turtles. There were no terrestrial mammalian predators on this island. The only predators of the clutches were crabs, which preyed on eight nests, which was 18.2% of nests, but accounted for a loss of only 23 eggs, from an estimated total of 2237 eggs laid (1.2%). The highest level of predation by crabs was observed in the nest located below the higher high water zone. Turtles selected preferred habitat for nesting, with most nests laid on the slope between the dune and the recent high tide mark, either in bare sand, grass or under trees or shrubs. For all nesting activity, 86.5% of nests were located on the slope, 12.2% on the 1 st dune and 1.4% below slope where they would be inundated by higher high tides. Health and injuries None of the nesting turtles at Avoid Island displayed recent fractures, though one turtle had relatively recent evidence of a shark attack with bite marks on the right shoulder and teeth rake marks along the carapace. Three turtles displayed healed scars from propeller damage and another two had healed major fractures to the carapace (Figure 8). No fibropapilloma tumours were observed on any of the turtles. Sand Temperature Monitoring Temperature profiles since 2012 were successfully downloaded from the data loggers in both the sunny and shady locations (Figure 9). Temperatures from the sunny location on the 1 st dune indicate that during the and seasons, similar locations would have produced mostly female hatchlings, but that during the season, mostly males would have been produced (Figure 10). Temperatures from the shade location on the 1 st dune indicate that temperatures in partial shade vary around the pivotal temperature for flatback turtles and would be expected to produce both female and male hatchlings (Figure 11). DISCUSSION This study has conducted the fourth year of monitoring nesting flatback turtles at Avoid Island, which is a moderate - sized nesting population towards the northern extremity of the breeding range for the eastern Australian stock. The numbers of individual tagged flatback turtles, track counts, and clutches laid during the breeding season were less than that recorded for the and (FitzSimmons 2013; FitzSimmons and Limpus 2014) breeding seasons (Figure 5). It is expected that there will be some yearly fluctuation in the numbers of turtles 8

9 nesting and the breeding season had a higher number of track counts than in the census where there were 63 crawls and an average of 4.5 (S.D. = 3.3) crawls observed per night. Beach erosion from Cyclone Dylan in 2014 was still apparent on South Beach, particularly with regard to a steeper dune profile, making limited access to the 1 st dune by turtles, but much of the slope below the dunes has filled in (Figure 6). On North Beach, the northern end of the beach continues to have inundation of all clutches laid below the 1 st dune on the higher tides (Figure 7). Hatchling production from Avoid Island during the breeding season was likely compromised for any clutches laid after the third week of December due to erosion from Cyclone Marcia, given the average incubation duration for flatback turtles is 53.4 days (range 47-58) for the Bundaberg coast (Limpus 2007). The proportion of new recruits has continued to fall each season, by 11.5% from to and by an additional 16.6% in All remigrants in were originally tagged on Avoid Is. To date, only two turtles originally tagged at Wild Duck Island have been observed on Avoid Island, once in the season and once in It is too soon to compare the nesting behaviour and nesting success of new versus remigrant turtles until more of the turtles in the population have been tagged. Existing management at Avoid Island is providing an important island nesting site that is free of predation by pigs, dogs, foxes and goannas, which are a potential problem at mainland sites. ACKNOWLEDGEMENTS The Avoid Island flatback turtle project was conducted as a cooperative project between the Queensland Trust for Nature (QTFN), Wild Mob, the University of New South Wales and the Turtle Conservation Project of the Threatened Species Unit, Department of Environment and Heritage Protection. Ben O Hara, Director of QTFN provided logistic support, organised transport and supplied accommodation for the field studies. Thanks to Kevin and Marie English for transporting equipment by barge and for keeping the airstrip and paths mowed. Thanks to Glen Leigh-Smith of Island Air for our safe transport. Thanks to the Wild Mob team of Andrew Elphinstone and Amanda Scrivernor, Jaz Lawes from University of New South Wales faculty and all student volunteers. Thanks to students Aly Ross, Charlotte Beloe and Wayne Hillier who came back after the nesting census period and helped dig up emerged clutches. Everyone s assistance is gratefully acknowledged. REFERENCES FitzSimmons, N. N Avoid Island Flatback Turtle (Natator depressus) Nesting Study Final Report to Queensland Trust for Nature. (20 February 2013). FitzSimmons, N. N. and Limpus, C. J. (2014). Marine Turtle Nesting Populations: Avoid Island Flatback Turtles, breeding season. Department of Environment and Heritage Protection, Queensland Government: Brisbane. Report produced for the Ecosystem Research and Monitoring Program Advisory Panel as 9

10 part of Gladstone Ports Corporation Ecosystem Research and Monitoring Program. 16 pp. Jones, M. and Venz H Queensland Turtle Conservation Project: Avoid Island Flatback Turtle Study, Report to EPA Tenure Actions Branch and Queensland Trust for Nature. 31 pp. Limpus, C. J. (1985). A study of the loggerhead turtle, Caretta caretta, in eastern Australia. PhD thesis, Zoology Department, University of Queensland. Limpus, C. J. (1992). Estimation of tag loss in marine turtle research. Wildlife Research 19, Limpus, C. J A biological review of Australian marine turtles: 5. Flatback turtle, (Natator depressus) (Garman). State of Queensland, Environmental Protection Agency. ISBN Limpus, C. J., Parmenter, C. J., Baker, V., and Fleay, A. (1983). The Crab Island sea turtle rookery in north eastern Gulf of Carpentaria. Australian Wildlife Research 10, Limpus C.J., Parmenter C.J. and Chaloupka M. (2013). Monitoring of Coastal Sea Turtles: Gap Analysis 5. Flatback turtles, Natator depressus, in the Port Curtis and Port Alma Region. Department of Environment and Heritage Protection Report produced for the Ecosystem Research and Monitoring Program Advisory Panel as part of Gladstone Ports Corporation s Ecosystem Research and Monitoring Program. 26 pp. 10

11 Table 1. Tagging history of flatback turtles, Natator depressus, recorded nesting at Avoid Island during 23 November 06 December Tagging history of turtles N First time tagged females (Primary tagged turtles) 34 Recaptures from past nesting seasons at Avoid Island Recaptured with tags previously recorded at Avoid Island (n =31) o 2007 (only) 6 o 2007, o 2012 (only) 20 o Recaptured with tag scars only, previously applied 3 tags lost, identified from PIT identification TOTAL 68 Table 2. Nightly census of nesting flatback turtles, Natator depressus, at Avoid Island during 23 November 06 December 2014: track count, observed clutches laid and clutches of hatchlings emerging. Date No. tracks No. clutches laid No. clutches of hatchlings emerged 23 Nov Nov Nov Nov Nov Nov Nov Nov Dec Dec Dec Dec Dec Dec Total

12 Table 3. Summary of curved carapace measurements and remigration intervals of nesting flatback turtles, Natator depressus, at Avoid Island during the 23 November 6 December 2013 census period. 1 st breeding season and previously untagged remigrants (primary taggings) Curved carapace length (cm) Mean SD Range N All known remigrant turtles All Turtles Remigration interval (yr) All remigrant turtles Table 4. Flatback turtle, Natator depressus, nest descriptions, incubation and hatchling emergence success at Avoid Island during the breeding season. Mean SD Range # Clutches Census Marked clutches Eggs per clutch Hatching success of eggs (%) Hatchling emergences success (%) Nest depth Clutches outside Census and found accidentally Eggs per clutch Hatching success of eggs (%) Hatchling emergences success (%) Nest depth Clutches found by observing hatchling tracks Eggs per clutch Hatching success of eggs (%) Hatchling emergences success (%) Nest depth

13 Figure 1a. Location of Avoid Island in relation to nearby landmarks. Figure 1b. Turtle nesting beaches at Avoid Island and infrastructure locations. 13

14 15 Undetermined nesting success (n = 2) Did not lay (n = 21) Laid (n = 72) FREQUENCY Oct 1 Oct 7 Oct 14 Oct 21 Oct 28 Nov 1 Nov 7 Nov 14 DATE Nov 21 Nov 28 Dec 1 Dec 7 Dec 14 Dec 21 Figure 2. Nightly number of flatback turtles, Natator depressus, ashore for nesting on Avoid Island during the standard mid season census period in 23 November 6 December FREQUENCY OF NESTING CRAWLS Undetermined nesting success (n = 2) Did not lay (n =21) Clutches laid (n = 72) A1 A2 A3 NESTING BEACH Figure 3. Frequency distribution of nesting crawls (tracks) and nesting success by beach location at Avoid Island during 23 November 6 December A1 = North Beach, A2 = Middle Beach, A3 = South Beach. 14

15 20 Measured females (n = 67) 15 FREQUENCY CURVED CARAPACE LENGTH (cm) Figure 4. Size frequency distribution of nesting flatback turtles at Avoid Island during the breeding season. TOTAL COUNT 90 Mean tracks/night Total tagged females 70 Total clutches BREEDING SEASON MEAN TRACKS PER NIGHT Figure 5. Comparison per season of total number of nesting females, total clutches laid and mean track counts per night during the mid-season nesting census of flatback turtles, Natator depressus at Avoid Island. 15

16 Figure 6. Beach profile of South Beach, Avoid Island after Cyclone Dylan (Mar 2014), showing extensive erosion, and before Cyclone Marcia (Feb 2015), showing the filled in beach profile. (Mar 2014 photo courtesy A. Elphinstone) Figure 7. Northern end of North Beach, Avoid Island is where turtle nesting locations are inundated at the higher high tides, photo 18 Feb 2015, just prior to Cyclone Marcia. 16

17 Figure 8. Nesting flatback turtles with healing fracture and damage, Avoid Island, December Figure 9. Locations of multi-year temperature probes in shaded and sunny flatback turtle nesting locations on the first dune slope, Avoid Island, February

18 Figure 10. Temperature profile from a sunny nesting location on the 1 st dune slope, Avoid Island, February

19 Figure 11. Temperature profile from a sunny nesting location on the 1 st dune slope, Avoid Island, February