Status of saltwater crocodiles in the Kimberley...Fukuda, Y., Whitehead, P. and Boggs, G. (2007)...
Transcript of Status of saltwater crocodiles in the Kimberley...Fukuda, Y., Whitehead, P. and Boggs, G. (2007)...
Status of saltwater crocodiles in the Kimberley.
KIMBERLEY MARINE RESEARCH PROGRAM NODE
PROJECT 1.2.3 – DR ANDREW HALFORD- DPAW
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
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
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
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
West Kimberley Survey Locations
Prince Regent
Roe River
Prince Regent River System
Maps of
Messel et al. 1987
Main Objective – abundance/size structure (1978…….1986.............................2015)
Survey Methods
Spotlighting Biopsy Sampling
Prince Regent Crocodile Surveys July 2015
N=708
Recruitment - Hatchlings
31 67
5
10
Cre
ek A
20 5 5
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
Crocodiles (5-7 feet)
Growth rate of Prince Regent Crocodile Populations
Comparison with Adelaide River (NT)
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)
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
Nesting Habitat
Most popular
West Kimberley
NT study - 4500 nests / 87% freshwater or mildly saline
Most popular
Roe River – salt tolerant sedge
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.
Other Objectives
o Develop Standardised Methodology • SOP’s • Methods Paper in review – Biopsy pole
o Develop skills in staff and TO’s
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
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