What I learned from Limpus, Carter and Hamann (2001) and Quantifying a Nesting Season Identifying Sussing out Michael Guinea School of Environment Charles Darwin University Darwin 0909
Whole of season monitoring Bramble Cay Track counts Nesting success Tagging of individuals Marking nests Hatching success
Figure 5 Nightly successful nesting and unsuccessful tracks
Figure 6 Cumulative arrivals and departures of nesters with available nesters at any time
Nesting Season at Scott Reef Location Sahul Shelf Previous reports Bob Prince early 1990s Kellie Pendoley early 1990s and 2000s Nesting numbers highly variable seasonality poorly defined Mick Guinea 1994, 2006, 2008, 2009, 2010, 2012
Sandy Islet, Scott Reef, Indian Ocean
Genetic Stocks of Australian Breeding Green Turtles : 1 = southern GBR; 2 = Coral Sea; 3 = northern GBR; 4 = Gulf of Carpentaria; 5 = Ashmore Reefs; 6 = Scott Reef; 7 = Northwest Shelf.8 = The Aru Islands Indonesian breeding stock (Dutton et al. 2002).
Sandy Islet (300 m x 70 m)
Sandy Islet Structures
Population of greens and hawksbills
Time Line of Green Turtle Tagging at Sandy Islet, Scott Reef Cumulative Number of Green Turtles tagged 600 500 400 300 200 100 0 May- 90 Sep- 91 Jan- 93 Jun- 94 Oct- 95 Mar- 97 Jul- 98 Dec- 99 Apr- 01 Sep- 02 Jan- 04 May- 05 Oct- 06 Feb- 08 Jul- 09 Date Nov- 10 Number of Tagged Turtles
Surveys 2006 2010 (WEL Surveys) Date Number of nights Time Ashore (hr) #Green Turtles tagged 15 25 Feb-06 2 10 Sep-06 23 29 Nov-06 27 31 Aug-08 28 Sep- 3 0ct 08 10 16 Dec-08 25 Jan 1 Feb 2009 29 Jan 11 Feb 2010 Total 3 1 5 2 6 7 7 13 44 24.0 9.0 45.0 26.0 35.0 46.5 67.5 81.75 334.75 29 0 92 10 4 107 193 54 489 Mean # of tracks /night ± sd 16.2 ± 4.87 0 23.6 ± 7.57 9.3 ± 1.15 7.8± 5.89 53.1 ± 16.87 71.9 ± 6.98 13.2 ± 5.43
Maximum information is gained by a 14 day survey in the middle of the nesting season When is the middle of the season? Which turtles are the new arrivals? 100 90 80 70 60 50 40 30 20 10 0 0 20 40 60 80 100 120 140? Percentage Day of Nesting Season New Arrivals Departures Available Nesters Hatched Nests
Need to suss out the Nesting Season Cumulative Frequency Distributions Normal curve Sigmoid curve Logistic equation Which data sets are useful? How best to do it?
Solver (add in) Excel
Scott Reef 2008-9 Season Scott Reef 2008/2009 4000 3000 2000 1000 0 21-Jul-08 9-Sep-08 29-Oct-08 18-Dec-08 6-Feb-09 28-Mar-09 17-May-09 6-Jul-09 Date Cum Nest Logistic Predicted Values Cumulative Number of Nests
1/02/2009 8/02/2009 25/01/2009 18/01/2009 120 100 80 60 40 20 0 Track and Nest Data Scott Reef 2008-09 14/09/2008 21/09/2008 28/09/2008 5/10/2008 12/10/2008 19/10/2008 26/10/2008 2/11/2008 9/11/2008 16/11/2008 23/11/2008 30/11/2008 7/12/2008 14/12/2008 21/12/2008 28/12/2008 4/01/2009 11/01/2009 Date Tracks + Nests Total Tracks 31/08/2008 7/09/2008 24/08/2008 Number of tacks
Delambre Island, Pilbara, WA
Pronounced summer nesting Flatback population Delambre Nests 2010/2011 1400 1200 1000 800 600 400 200 0 19/09/2010 9/10/2010 29/10/2010 18/11/2010 8/12/2010 28/12/2010 17/01/2011 6/02/2011 26/02/2011 Date Cum Nest Logistic Predicted Values Cumulative Number of Nests
Flatbacks Delambre Nests 2011/2012 2000 1500 1000 500 0 14/09/2011 4/10/2011 24/10/2011 13/11/2011 3/12/2011 23/12/2011 12/01/2012 1/02/2012 21/02/2012 Date Cum Nest Logistic Predicted Values Cumulative Number of Nests
Bare Sand Island, NT
Protracted winter nesting population Bare Sand Island 2005 700 600 500 400 300 200 100 0 8-Apr-05 28-May-05 17-Jul-05 5-Sep-05 25-Oct-05 Date Cum Nest Logistic Predicted Values Number of nests
Flatback (average nesting numbers) Bare Sand 2011 Nests 1000 500 0 Cumulative Numbers 26-Feb-11 17-Apr-11 6-Jun-11 26-Jul-11 14-Sep-11 3-Nov-11 23-Dec-11 Date observed turtles Logistic
Flatback (low nesting numbers) Bare Sand Island 2012 400 300 200 100 0 1/04/20 12 21/04/2 012 11/05/2 012 31/05/2 012 20/06/2 012 10/07/2 012 30/07/2 012 19/08/2 012 8/09/20 12 Date Cum Nest Logistic Predicted Values Cumulative Number of Nests
Estimating the nesting population Number of nests per female per season Inter seasonal changes in internesting interval warm years vs cool years Intra seasonal changes in internesting interval early vs middle vs late in season Weather conditions warm calm seas = short interval (10 days) cool choppy seas = longer interval (21 days)
Is the logistic equation a useful descriptor of the nesting population? How much noise is in this metric? # Tracks > # nests > # turtles And what are we trying to measure? Is it the number of tracks? - crude metric Or number of nests? less crude metric Or number of turtles? better metric but difficult Or the contribution the nesting beach makes to the population i.e. nesting, hatching and emergence success?
My final 2 cents worth Change is inevitable! Keep on recording (record heaps) Be alert to changes Move off your patch once and a while If every nesting season was the same we would learn nothing new.
Thank You and thanks to The authors Col Limpus, Dave Carter and Mark Hamann, The late Daryl Riseley who left his delightful scribbles of the logistic equation on serviettes, table napkins, backs of envelopes and on my mind Volunteers, beach walkers, turtle whispers, and flatback fondlers of Bare Sand and Delambre Islands Rio Tinto Ltd Cape Lambert Woodside Energy Limited AusTurtle Inc