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