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Status of saltwater crocodiles in the Kimberley.
KIMBERLEY MARINE RESEARCH PROGRAM NODE
PROJECT 1.2.3 – DR ANDREW HALFORD- DPAW
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Status Quo
• No surveys in West Kimberley rivers for ~30 years
• 1987 – pop’n estimated at only 2500 individuals • Recovering from unregulated harvesting which ceased in
1969. • Current understanding – increased numbers, increasing
range?
• East Kimberley, Cambridge Gulf river systems surveyed regularly – 1992-2013, croc harvesting program
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NT Croc Densities
• Use NT experience to inform WA surveys
• Continuous research/surveys since the 1980’s
• Population considered recovered from hunting by 2000 (Webb et. al. 2000)
• Expect similar pattern in WA
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Ord River Croc Densities
• East Kimberley has long-term population estimates – Cambridge Gulf
• Harvesting program – recently stopped
• Population increased rapidly from 2000 and still increasing (Webb et. al. 2014)
• Similar population growth to NT
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Dredging Science Node
West Kimberley Surveys
• Impossible to replicate the spatial scale of Messel’s work today - surveyed every major river in the Kimberley, NT, QLD
• Concentrate on breeding (nesting) hotspots • Use of models and localised monitoring to
inform more broadly
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West Kimberley Survey Locations
Prince Regent
Roe River
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Prince Regent River System
Maps of
Messel et al. 1987
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Main Objective – abundance/size structure (1978…….1986.............................2015)
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Survey Methods
Spotlighting Biopsy Sampling
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Prince Regent Crocodile Surveys July 2015
N=708
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Recruitment - Hatchlings
31 67
5
10
Cre
ek A
20 5 5
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Non-hatchling crocodiles N=35
N=75
N=267
N=63
N=57
N=171
N=189
N=247
N=708
ALL MAIN STH ARM
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Crocodiles (5-7 feet)
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Growth rate of Prince Regent Crocodile Populations
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Comparison with Adelaide River (NT)
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Prince Regent Adelaide
Density (no hatchlings) 3 per km 4.2 per km
Ratio large(>6ft)/small (2-6ft)
0.6 1.7
% 5-6ft crocodiles 18.8%; Sth Arm(25%) 8.2%
Large Crocodiles (>10ft)
5 63
Biomass Density 91.4kg per km 274.02kg per km
Comparison with Adelaide River (NT)
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Model of Crocodile Population Dynamics
o The tidal waterways of northern Australia are categorized into Type 1, 2 or 3 according to their salinity signatures.
• Type 1 – Major Freshwater Input, good nesting
habitat – typical NT rivers • Type 2 – No/little freshwater, hypersaline, no nesting • Type 3 – In between other 2, very little nesting • Type 2 and 3 get crocodiles from Type 1
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Nesting Habitat
Most popular
West Kimberley
NT study - 4500 nests / 87% freshwater or mildly saline
Most popular
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Roe River – salt tolerant sedge
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Fukuda, Y., Whitehead, P. and Boggs, G. (2007) Broad-scale environmental influences on the abundance of saltwater crocodiles (Crocodylus porosus) in Australia. Wildlife Research 34(3): 167-176
Modelling/prediction
(1) the ratio of total area of favourable wetland vegetation types (Melaleuca, grass and sedge) to total catchment area, (2) a measure of rainfall seasonality, namely the ratio of total precipitation in the coldest quarter to total precipitation in the warmest quarter of a year, and (3) the mean temperature in the coldest quarter of a year.
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Other Objectives
o Develop Standardised Methodology • SOP’s • Methods Paper in review – Biopsy pole
o Develop skills in staff and TO’s
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Implications for Management
o Healthy crocodile populations, recovering well o Atypical environments in West Kimberley so
future recovery dynamics unclear o Increased interactions between crocodiles and
humans • Need more data on numbers and size
structure from other river systems • Quantifying nesting habitat is crucial to
understanding the future dynamics of crocodiles
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Acknowledgments • The State Government of Western Australia and WAMSI
partners for funding this research.
• DPaW collaborators
Danny Barrow, Winston Kay, Todd Quartermaine, Daryl Moncrief, Crew of PV Worndoom
• Traditional owners of the Kimberley
Dredging Science Node