Download Summary of Flatback turtle (Natator depressus)

Summary of Flatback turtle (Natator
depressus)
monitoring data for the Jardine River
site 2012-2014
2012-2014
Compiled by
Northern Peninsula Area Regional Council/Apudthama
Land and Sea Ranger Group
Threatened Species Unit Environment and Heritage
Protection
Western Cape Turtle Threat Abatement Alliance
Acknowledgements
This report presents the results of flatback turtle monitoring activities undertaken by the
Indigenous Land and Sea Rangers working under the Northern Peninsula Area Regional
Council and Apudthama Land Trust. These activities have been supported throughout by the
Western Cape Turtle Threat Abatement Alliance (WCTTAA) and the Threatened species Unit
of the Queensland Department of Environment and Heritage Protection. The authors would
also like to acknowledge the traditional owners upon whose land these activities occurred
and the Queensland Government for providing funding for monitoring activities.
Most importantly, none of this would have been possible without the tireless effort and
dedication of the entire ranger team.
Citation
Freeman, A.B., Strevens, W., Bell. I. and Karam, J. 2015. Summary of flatback turtle monitoring
data for the Jardine River site 2012-2014.
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ii
Cover images Alastair Freeman (top) middle and bottom (Kerry Trapnell)
Table of Contents
Acknowledgements ................................................................................................................................................. ii
List of Figures............................................................................................................................................................ iv
List of Tables ............................................................................................................................................................. iv
Abbreviations............................................................................................................................................................ iv
1
Background................................................................................................................................................... 1
2
Monitoring area .......................................................................................................................................... 2
3
Methodology ............................................................................................................................................... 3
4
Results ............................................................................................................................................................ 5
5
4.1
Turtle Monitoring .............................................................................................................................. 5
4.2
Measurements .................................................................................................................................... 6
4.3
Nesting turtle distribution along transect ............................................................................... 7
4.4
Nesting .................................................................................................................................................. 8
4.5
Nesting habitat .................................................................................................................................. 9
4.6
Hatching success ............................................................................................................................ 11
4.7
Satellite tracking 2014 .................................................................................................................. 11
4.8
Other turtle species recorded.................................................................................................... 12
Discussion................................................................................................................................................... 12
Management Summary ...................................................................................................................................... 16
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iii
References cited .................................................................................................................................................... 17
List of Figures
Figure 1: Study site locality in far northern Cape York .............................................................................. 2
Figure 2: Jardine River mouth monitoring transect .................................................................................... 2
Figure 3: Apudthama Land and Sea rangers tagging a flatback turtle, Jardine River mouth
monitoring site (image Kerry Trapnell) ............................................................................................................ 3
Figure 4: Location of Indicator nests with data loggers on Jardine river census beach................ 4
Figure 5: Satellite tagged flatback turtle (Image Ian Bell)......................................................................... 5
Figure 6: Nesting interval (days) for returning turtles (n=114). .............................................................. 6
Figure 7: Turtle records with accurate locality data for the 2013 (n=395) and 2014 (n=606)
nesting seasons......................................................................................................................................................... 7
Figure 8: Turtle nest habitat categories ........................................................................................................... 9
Figure 9: Nesting flatback turtle in foredune (Image Kerry Trapnell)................................................ 11
Figure 10: Track map of satellite tagged flatback turtles tagged in 2014 ....................................... 12
Figure 11: Pig shot in 2006 on west coast of Cape York with flat back hatchlings in stomach
(Image Lee and Kerlin) ........................................................................................................................................ 14
List of Tables
Table 1: Indicator nest locations and establishment and data logging dates. ................................. 4
Table 2: Summary statistics for CCL measurements for flatback turtles measured at the
Jardine River monitoring site during the 2013 and 2014 monitoring seasons (excluding within
season recaptures) ................................................................................................................................................... 7
Table 3: Number of flatback nests recorded on transect over three years of monitoring........... 8
Table 4: Predation levels recorded for flatback turtle nests over monitoring period .................... 8
Table 5: Number of feral pigs killed in helicopter control operations ................................................. 9
Table 6: Summary of nesting habitat recorded in 2013 and 2014 ........................................................ 9
Table 7: Summary of nest temperature data collected in 2014 .......................................................... 10
Table 8: Clutch size and nesting success recorded in the 2014 monitoring season ................... 11
Table 9: Non flatback turtle nests recorded 2012-2014. ........................................................................ 12
Abbreviations
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iv
CCL
EHP
GPS
NPARC
PDA
Curved carapace length
Queensland Department of Environment and Heritage Protection
Global Positioning System
Northern Peninsula Area Regional Council
Personal digital assistant
1
Background
The flatback turtle (Natator depressus) is an endemic species with all rookeries confined to
northern Australia from the Exmouth area of Western Australia to the south east coast of
Queensland. It is currently listed as Vulnerable under the Environmental Protection and
Biodiversity Conservation Act (EPBC) and Vulnerable under the Queensland Nature
Conservation Act (NCA). This turtle is a species that feeds in the waters over the Australian
continental shelf north to the Gulf of Papua New Guinea and coastal waters of West Papua in
Indonesia. Beyond the Australian continental shelf, the species has been recorded in the
coastal waters of Kei in south-eastern Maluku, Indonesia
The largest breeding aggregations for this species occur on Crab Island and the adjacent
west coast of Cape York Peninsula south to Kowanyama , as well as on some of the islands of
western Torres Strait. Nesting also occurs along the entire Northern Territory coastline and
into Western Australia as far south as Exmouth and along parts of the coastline in mid and
south-east Queensland (Limpus, 2007). This population forms part of genetically distinct
management unit which encompasses turtles from the western Torres Strait, Gulf of
Carpentaria and Northern Territory as far west as Darwin (Fitzsimmons and Limpus, 2014).
The current monitoring is part of a larger project that aims to study the breeding biology,
habitat utilisation, diets and health of flatback turtles originating from Jardine River beach
and Crab Island, in the Northern Peninsula Area (NPA) region, Queensland. The nesting turtle
monitoring program has been established to determine what contribution flatback turtles in
NPA are making to the greater flatback populations and Queensland Turtle Conservation
Project. Annual monitoring of turtle nesting beaches provides valuable information about the
status of nesting populations, detects changes within the population, and measures the
effectiveness of planning and management tools. The Queensland Turtle Conservation (QTC)
project is a long-term research, monitoring and conservation management project in
operation within the Department of Environment and Heritage Protection (EHP). The data
collected is collated within a central EHP database and is summarised in annual reports
produced by EHP staff and volunteer team leaders.
Year-round nesting, with a June to August winter peak is the norm along the western Cape
York coastline with average clutch sizes of around 50 eggs (Limpus, 2007). Flatback turtles
nest on the Jardine River beach and it is now a major nesting index site. Data have been
collected on nesting activity at this site during the nesting seasons of 2012, 2013 and 2014.
Nesting activity was monitored by Apudthama Land and Sea Rangers with the assistance of
Threatened Species Unit staff from Environment and Heritage Protection. During 2013 and
2014, data on nesting turtles were also collected. This report summarises the nesting and
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turtle data collected during these three monitoring seasons.
2
Monitoring area
Nest monitoring occurs along the coastline
adjacent to the Jardine River in far northern Cape
York Peninsula (Figure 1).
Turtles are monitored on the beach along a 10
kilometre transect from the western side of the
mouth of the Jardine River to the tip of a small,
sandy peninsula to the south west (Figure 2).
Figure 1: Study site locality in far northern Cape York
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Figure 2: Jardine River mouth monitoring transect
3
Methodology
Monitoring of nests has occurred over three nesting seasons (2012-2014). The position,
habitat and any signs of predation on nests were recorded with a handheld PDA (personal
digital assistant) using Cybertracker software.
Monitoring of turtles took place over a period of four and half weeks in 2013 and eight
weeks in 2014. During this time rangers – and some volunteers – were based in a camp
adjacent to the nesting beaches. The beaches were checked by rangers for nesting activity at
intervals during the early evening and into the night. Nesting turtles were observed as they
were encountered coming ashore. As each turtle began laying eggs, rangers recorded the
location of nesting activity with the GPS function of the PDAs. Turtles were checked for
flipper tags and tag numbers of recaptures were recorded. Untagged turtles were tagged
with a flipper tag and curved carapace length (CCL) was recorded using a dress maker’s tape
measure. The position of each nest on the beach was also recorded according to whether it
was on or above the high tide mark, in the dunes or on the edge of the adjacent vegetation.
Figure 3: Apudthama Land and Sea rangers tagging a flatback turtle, Jardine
River mouth monitoring site (image Kerry Trapnell)
Data loggers were placed in ten indicator nests to record temperature, of which 9 were
recovered. These loggers were Thermochron (DS1921G) buttons housed in small plastic
cases, as used for the storage of SD memory cards. These were placed in the top of nesting
chambers after laying was completed, prior to burying of the nest. Temperature data loggers
were placed in nests between July and September 2014. Details of the locations,
establishment dates and start and end dates of temperature data recording are provided
below (Table 1). All data loggers were programmed to record temperatures in degrees
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3
Celsius at half hour intervals.
Table 1: Indicator nest locations and establishment and data logging dates.
Nest
number
1
2
3
4
5
6
7
8
9
10
Latitude
Longitude Date est'd
Temp Start
Temp End
-10.9144
-10.9144
-10.9146
-10.9146
-10.9145
-10.9147
-10.9147
-10.9155
-10.9163
-10.9166
142.2023
142.2051
142.2064
142.2065
142.2059
142.1991
142.2074
142.1944
142.1917
142.1891
24/07/2014
not recovered
24/07/2014
24/07/2014
24/07/2014
3/08/2014
3/08/2014
6/08/2014
7/08/2014
2/09/2014
5/09/2004
24/07/2014
24/07/2014
24/07/2014
24/07/2014
24/07/2014
6/08/2014
6/08/2014
8/08/2014
1/09/2014
1/09/2014
5/09/2014
5/09/2014
5/09/2014
15/09/2014
15/09/2014
18/09/2014
19/09/2014
15/10/2014
The location of data loggers are shown in Figure 4. All indicator nests were located in the
4
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Figure 4: Location of Indicator nests with data loggers on Jardine river census beach
most easterly 2km of the 10km census area. This may not be representative of the entire
census area, though it is the area of highest density nesting, as described in the results
section below.
Satellite tracking is an ideal method to study migration, movement and habitat use, and sea
turtles are ideal candidates to use this technology on, as they frequently come to the surface
to breathe. Indeed satellite technology has been used in many turtle studies to great effect.
In 2014, two satellite transmitters were purchased by the ranger program to place on
flatback turtles from the Jardine River monitoring area. These were SPLASH tags, data
archiving tags that transmit to the Argos satellite system.
These were secured on two
females using a harness system (Figure 5).
Figure 5: Satellite tagged flatback turtle (Image Ian Bell)
4
Results
4.1 Turtle Monitoring
From the 6th of August to the 9th September 2013 a total of 367 (not including recaptures)
nesting flatback turtles were recorded and tagged during the monitoring period. Twentyfive out of the 367 turtles were recorded attempting to nest twice over the period of the
monitoring. One further turtle was recorded as an inter-season nester, based on a tag scar
on the flipper. Unfortunately, as the tag was not present, it was not possible to establish
where this individual had originally been tagged.
This was the only turtle recorded that
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showed signs of having been tagged prior to 2013.
Between the 8th of August and 27th September 2014 a total of 518 individual flatback turtles
– not including recaptures – were recorded and tagged attempting to nest during the
monitoring period. Of these 518 turtles, 89 individuals were observed attempting to nest
45
40
No of turtles recorded
35
30
25
2013
20
2014
15
10
5
0
0-5
6-10 11-15 16-20 21-25 26-30 31-35 36-40 41-45 46-50 51-55
No. of days between nesting attempts
Figure 6: Nesting interval (days) for returning turtles (n=114).
twice and two individuals observed three times over the period of the monitoring.
The combined data from 2013 and 2014 indicates that the interval between the return of
known individual nesting turtles varies from zero (same night) to 52 days with the single
largest number of turtles returning after an interval of 16 to 20 days and 31 to 35 days
(Figure 6).
A total of 404 nesting turtles were observed in 2013 whilst 671 nests were
recorded indicating that not all turtles were observed when they came ashore to nest.
4.2 Measurements
Curved carapace length (CCL) varied from 32 to 99cm in length (n=1028). However for the
purposes of analysis those below 75cm CCL have been excluded based on a comparison with
CCL measurements taken from flatbacks attempting to nest on nearby Crab Island. Here the
smallest CCL recorded from 14 nesting seasons over 36 years between 1976 and 2014 was
75.5cm CCL (n= 2615). The difference in minimum size between these two sites is thought to
be attributable to recorder error rather than an inherent difference in the size range between
the sites. At the same time the actual number of turtles with a CCL below 75cm in the
current dataset numbered 20, less than 2% of the total number of turtles measured
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(n=1008).
Table 2: Summary statistics for CCL measurements for flatback turtles measured at the Jardine River
monitoring site during the 2013 and 2014 monitoring seasons (excluding within season recaptures)
Year
Number
2013
2014
364
532
Max
(cm)
98.5
99.0
Min
(cm)
75.5
75.0
Mean
(cm)
88.3
88.1
StDev(cm)
3.43
3.10
4.3 Nesting turtle distribution along transect
The distribution of turtles recorded along the beach transect was highly uneven (Figure 7). A
total of 998 records had accurate location data, of these 938 (94%) were recorded in the first
3.35km (34%) of the 10km transect. Just over half of the transect length contained 994
(>99%) of all the sightings.
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Figure 7: Turtle records with accurate locality data for the 2013 (n=395) and 2014 (n=606) nesting seasons.
4.4 Nesting
Over the three monitoring seasons, a total of 2240 nests were recorded along the transect.
The highest number of nests was recorded in 2012, with a steep decline in numbers in 2013
and 2014 (Table 3).
Table 3: Number of flatback nests recorded on transect over three years of monitoring
Year
No. of nests
Days
monitoring
2012
2013
2014
923
671
646
31
57
45
Nests /days
of
monitoring
30
12
14
As with the nesting turtles, nest distribution along the transect was strongly associated with
the north eastern end of the transect with 96% (n=2160) of all nests recorded in the first
5.6km of the 10km transect over the three years.
Over the three years of monitoring, nest predation levels have been low with the highest rate
observed in 2013, when 8.3% of observed nests were predated. This puts incubation success
well above the accepted minimum of 70% required for sustainable nesting success. Predators
were a mix of humans, dingo (Canis lupus dingo), goanna (Varanus sp.) and pig (Sus scrofa)
(Table 4).
Table 4: Predation levels recorded for flatback turtle nests over monitoring period
Year
2012
No. of nests
923
No. Predated
13
% predated
1.4
2013
671
56
8.3
2014
646
15
2.3
Predator
Human (n=6)
Goanna (n=6)
Unknown (n=1)
Dingo (n=11)
Pig (n=28)
Unknown (n=17)
Human (n=9)
Dingo (n=2)
Unknown (n=4)
Over this same period there has been a targeted feral pig control program in the area which
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has removed over 1100 pigs in the three years between 2012 and 2014 (Table 5).
Table 5: Number of feral pigs killed in helicopter control operations
Date
2012
2013
2014
2014
2014
Period
Total No.
killed
9 Dec-12 Dec
6 Dec-12 Dec
26 May-28 May
29 June-30 June
15 Sept-22 Sept
Flight
hours
337
339
130
159
203
17
16.5
5
7.5
25
No.
Pigs/flight
hour
19.8
20.5
26.0
21.2
8.1
4.5 Nesting habitat
Nesting habitat was recorded for 1327 turtles (671 in 2013 and 646 in 2014) based on the
categories shown in Figure 8. The most common location for turtle nesting was high on the
beach within the vegetation below dunes (Table 6).
Figure 8: Turtle nest habitat categories
Table 6: Summary of nesting habitat recorded in 2013 and 2014
Year
High tide mark
No of nests
2013
2014
79 (12%)
186 (29%)
Edge of
vegetation
No of nests
505 (75%)
334 (51%)
Dune system
No. of nests
87 (13%)
126 (20%)
Temperature loggers were placed in indicator nests at the time of laying. The selection of
nests to be monitored as indicator nests were selected at different times throughout the
monitoring period. Five indicator nests were established in late July, 3 in early August and
two in early September.
Temperature varied across nests and across months with a
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minimum temperature of 250C recorded in one nest in July and another in September. A
maximum temperature of 33.50C was recorded in one nest during September (Table 7). The
most extreme temperature variation was observed in indicator nest 10 where the difference
between maximum and minimum temperature was 8.50C. The next greatest variation in nest
temperature was a difference of 4.50C between maximum and minimum temperatures in
nest 5. Mean temperature between nests also varied across months; as high as three degrees
in July and August and four in September.
Table 7: Summary of nest temperature data collected in 2014 in indicator nest at the Jardine River monitoring site
Site
Jardine
1
Jardine
3
Jardine
4
Jardine
5
Jardine
6
Jardine
7
Jardine
8
25.9
0.378
25.0
26.5
337
27.3
0.470
26.5
28.0
337
27.0
0.450
26.0
28.0
337
28.6
0.512
27.5
29.5
337
27.0
0.715
25.5
28.5
1488
28.5
0.573
27.0
29.5
1488
28.2
0.609
27.0
29.5
1488
29.5
0.731
28.0
31.5
1488
28.5
0.692
27.0
30.0
1248
28.5
0.521
27.0
29.0
1248
28.2
0.544
26.5
29.0
1152
27.9
0.596
27.0
29.0
223
29.8
0.258
29.5
30.5
223
29.1
0.262
28.5
29.5
223
31.1
0.392
30.5
32.0
223
29.4
0.374
28.5
30.0
680
29.5
0.281
29.0
30.0
680
29.1
0.404
28.5
30.0
822
Jardine
9
Jardine
10
29.2
0.361
28.0
30.5
870
29.6
0.585
25.0
33.5
1372
July
Mean (0C)
St Dev (0C)
Min (0C)
Max (0C)
n
August
Mean (0C)
St Dev (0C)
Min (0C)
Max (0C)
n
September
Mean (0C)
St Dev (0C)
Min (0C)
Max (0C)
n
October
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10
Mean (0C)
St Dev (0C)
Min (0C)
Max (0C)
n
31.0
0.750
29.5
32.0
676
Figure 9: Nesting flatback turtle in foredune (Image Kerry Trapnell)
4.6 Hatching success
One nest was excavated in 2014 to ascertain hatching success (Table 8).
Table 8: Clutch size and nesting success recorded in the 2014 monitoring season
Clutch
Size
Hatched
Eggs (%)
52
48 (92)
Unhatched
dead
embryos
2
Unhatched
undeveloped
Unhatched
Unknown
1
1
4.7 Satellite tracking 2014
Two flatback turtles fitted with satellite tags on the 12th of September 2014, displayed two
very different trajectories (Figure 10). The first, named ‘Cecilia’, moved north on the day of
release into Torres Strait and along the coast of Papua New Guinea between Boigu and
Saibai island. Information from this tag was received for 60 days before communications
were lost. The second animal, ‘Kiku’ remained close to the Jardine River site for more than
two weeks and may have nested again during this period before moving south down the
west coast of Cape York Peninsula into the south-eastern portion of the Gulf of Carpentaria.
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Communication with this transmitter was lost after 169 days.
Figure 10: Track map of satellite tagged flatback turtles tagged in 2014
4.8 Other turtle species recorded
Over the course of the monitoring, the nests of five other species of turtle were recorded in
low numbers; loggerhead (Caretta caretta), green turtle (Chelonia mydas), leatherback turtle
(Dermochelys coriacea), hawksbill (Eretmochelys imbricata) and olive ridley (Lepidochelys
olivacea) (Table 9).
Table 9: Non flatback turtle nests recorded 2012-2014.
Species
2012
2013
2014
1
Loggerhead
1
Green
1
1
Leatherback
2
1
Hawksbill
3
1
2
Olive Ridley
2
2
1
This record is considered likely to be recorder error or misidentification
5
Discussion
In 2013 and 2014, a total of 1030 nesting turtles were recorded at the mouth of the Jardine
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River of these, 113 were observed attempting to nest more than once, 22 in 2013 and 91 in
2014. All of these were within season recaptures. One turtle was recorded with a tag scar
that indicated it had been banded in a previous year. However, as this individual no longer
had a tag it was not possible to determine where or when it had originally been tagged. The
interval between recorded sightings of tagged individuals varied between 0 and 52 days with
two distinct peaks at 16 to 20 and 31 to 35 days. Differences in the number of nests recorded
compared to number of turtles tagged suggests that not every turtle was observed every
time it came ashore to nest. This is an artefact of the fact that patrols are not conducted
throughout the entire night and travel time along the length of the transect is such that
turtles could have time to emerge, lay nests and return to the water before monitoring teams
reach them. Most marine turtles lay multiple clutches within a single nesting season at
approximately two-week intervals (Limpus et. al., 1993). Data from the present monitoring
suggest this is the case for flatbacks at the mouth of the Jardine River, although more data is
needed to confirm this.
The overall mean CCL of 88.2cm (n=896) recorded in the present study varies little from that
recorded for flatbacks on nearby Crab Island of 89.3cm (n=326) (Limpus, 2007) and 88.2cm
(n=69) (Sutherland and Sutherland, 2003). However, the range of CCL measurements at
these two sites is considerably smaller than that seen in nesting populations in south eastern
Queensland. This size difference, along with a number of other factors is indicative of a lack
of gene flow between these two breeding populations hence these two populations are
considered distinct management units (Limpus, 2007; Fitzsimmons and Limpus, 2014).
Measurements from the Jardine River site include a degree of error, given that many of the
measurements taken by rangers were rounded to the nearest centimetre. Rangers should be
encouraged to take more accurate measurements in future monitoring efforts.
Monitoring of turtle activity in 2013 and 2014, and recorded nest numbers between 2012
and 2014, indicate that the coastal area immediately west of the Jardine River remains a
significant mainland nesting area for flatback turtles.
The vast majority of this nesting
activity appears to be confined to the easternmost three to four kilometres of the census
beach. Beyond this, activity rapidly decreased along the ten kilometres to the south western
end of the surveyed transect beach. The reason for this is unknown although it has been
suggested that perched freshwater swamps immediately behind the dunes may be important
to successful nesting by seas turtles along the west coast of Cape York.
Having the
appropriate moisture level in nesting substrates is important to nesting success in sea turtles
(Johannes and Rimmer, 1984; Mortimer, 1990; McGehee, 1990).
Anecdotal evidence
indicates that freshwater soaks, and swamps behind the dunes on western Cape York may be
important in maintaining an appropriate moisture level on nesting beaches. The clumped
pattern of nesting activity at the mouth of the Jardine may be a reflection of this relationship.
The pivotal nest temperature is the temperature that theoretically produces a 50/50 sex ratio
in hatchlings. For flatback turtles the suggested pivotal temperature is 29.30c during the
13
Pivotal nest temperatures can have
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middle of the incubation period (Limpus, 2007).
significant impacts on sex ratios. At Mon Repos on Queensland’s east coast for example,
flatback hatchling sex ratios for the entire breeding season is biased towards females as a
result of high nest temperatures (Limpus, 2007). Whether a similar situation is occurring on
the northern tip of Cape York is unknown as there is not enough temperature data from the
Jardine River monitoring yet to assess this. Future monitoring efforts will also ensure that
indicator nests with temperature loggers are spread more broadly across the length of the
surveyed beach. This will assist in determining whether temperature differences play any role
in nesting site selection.
The difference in nest numbers recorded between 2012 and 2013-14 (Table 3) is of some
concern, although at this stage it is too early to tell if this is a long term downward trend,
methodological problem or cyclic population fluctuation. Only further monitoring will clarify
this. As the monitoring methods become clearly defined and standardised it is anticipated
that more accurate comparisons will be possible.
Nest predation rates were low within the area monitored between 2012 and 2014. This is
particularly evident when compared with other areas on the west coast of Cape York. For
example 70% of flatback turtle nests were depradated by feral pigs on the Pennefather
Beach over a 12 month period from May 2004 to May 2005 (Doherty, 2005). Marine turtle
nests – the majority of which were flatbacks – suffered depredation rates as high as 37% at
the same locality in 2007 (Whytlaw et. al., 2013). In 2006, a predation rate by feral pigs of
48% was observed in 52 marked nests on the Cape York coast south of Crab Island (unpub.
data).
Figure 11: Pig shot in 2006 on west coast of Cape York with flat back hatchlings
in stomach (Image Lee and Kerlin)
An ongoing and effective feral pig control program implemented by the NPARC/Apudthama
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Land and Sea Rangers combined with the ranger presence on the nesting beach during the
peak nesting period is almost certainly the reason for the low nest predation rates. Data
available indicate that other nest predators, which that are not controlled, such as dingos
and goannas are currently only having a minor impact, while the human take of eggs would
also appear to be negligible at this stage.
The satellite tagging of two females in 2014 was the first for individuals from the Jardine
River rookery site. The results so far have supported the view that the turtles in this
population forage in the waters of the Gulf Carpentaria and western Torres Strait as far north
as coastal Papua New Guinea (Figure 5).
Both turtles showed a strong attachment to
shallow, inshore coastal areas which is where this carnivorous species accesses the softbodied invertebrates that make up the majority of its diet (Curtis, 2012). While the results
from the present tracking have been excellent, this technology has some limitations related
to limited battery life, tag design and high costs, which prevent most research budgets
(including the current one) from acquiring a large sample size. Therefore, studies quite often
have to extrapolate population movement patterns based on a limited number of
individuals. If funding became available it would be worthwhile attaching more satellite tags
to flatback turtles from this area to gain a better understanding of proportions of the nesting
population foraging in the Torres Strait compared to those in the Gulf of Carpentaria.
A number of nests belonging to turtle species other than flatbacks were recorded (Table 9).
Of these species hawksbill and olive ridleys are known to nest nearby (GHD, 2010; Miller and
Limpus, 2012a and 2012b) on Crab Island, while green turtles are known to nest in the Torres
Strait (Miller and Limpus, 2012c). There are no records of loggerhead turtles nesting across
northern Australia from Lizard Island off eastern Cape York to the Ashmore Reef in northwestern Australia (Limpus 2009a) and without further evidence the record for this species
from 2012 is considered to be extremely unlikely and probably resulted from recording error
or misidentification. The leatherback nest records are potentially very important. Breeding by
this species is thought to no longer occur on the eastern seaboard of Australia with the only
confirmed nesting currently known from Australia being a small number of annual nesters on
Coburg Peninsula in the Northern Territory. In the past, the species was known to also nest in
Arnhem Land on the western edge of the Gulf of Carpentaria as well as in a few localities in
southeast Queensland and northern New South Wales (Miller and Limpus, 2012d; Limpus
pers. comm.). Recent anecdotal accounts of nesting from Cape York as well as non-nesting
records from western Cape York (Limpus, 2009b) means that their presence on the nesting
beaches within the monitoring area cannot be dismissed out of hand, however confirmation
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of their presence is needed.
Management Summary
Monitoring of this important mainland rookery should continue
Quantification of monitoring effort should be a priority for 2015 and onwards (i.e.
number of days beaches were patrolled over season number of times beaches were
checked in a night whether or not turtles were recorded)
Recording nesting success should be a priority for 2015 (clutch size, hatching success
and predated nests)
A more systematic and comprehensive program of nest temperature monitoring
should be developed
A continuation of the feral pig control should continue to be seen as a priority
Academic researchers should be encouraged to examine the relationship between
sand moisture levels, nesting activity and the freshwater swamp and wetland areas
behind the dunes
Every effort should be made to establish if leatherback sea turtles are nesting in this
area
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Continuing training to ensure accurate data recording using standard methods
References cited
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Publishing, pp. 197–-198.
Doherty, J. 2005. Ecological impact assessment of feral pig predation in marine turtle
breeding habitat on the west coast of Cape York. Unpublished thesis prepared for Charles
Darwin University, Darwin. 71pp.
Fitzsimmons, N.N. and Limpus, C.J. 2014. Marine turtle genetic stocks of the Indo-Pacific:
identifying boundaries and knowledge gaps. Indian Ocean Newsletter No 20: 2-18.
GHD, R. 2010. Queensland NRM Report for Caring for our Country. Overview of marine
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Johannes, R.E. and Rimmer, D.W. 1984. Some distinguishing characteristics of nesting
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Limpus, C.J. 2007. A biological review of Australian marine turtles. 5. Flatback turtle, Natator
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Limpus, C.J. 2009a. A biological review of Australian marine turtles. 1. Loggerhead turtle,
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