Kimberley survey nets plenty of crocs

Parks and Wildlife officers have conducted a capture and release survey of freshwater crocodiles (Crocodylus johnsoni) with Bunuba Rangers at Winjanna Gorge National Park in the West Kimberley in preparation for the arrival of cane toads.

DPaW West Kimberley conservation coordinator Tracy Sonneman says they aim to establish baseline ecological and biological data for the population before cane toads (Rhinella marina) appear.

"We were trialling something relatively new for Western Australia in capturing the crocodiles using nets," she says.

"It took a little bit of trial and error to get it right, then once we caught the crocodiles and they were restrained we were just getting whole piles of morphological data as well as taking genetic samples."

She says the exercise will add to the demographic data gained from regular spotlighting surveys.

"We go along at night time either on the banks or on a boat, depending on the body of water, and just use the spotlight to pick up the eye shine of the crocodile," she says.

"Then if we can get close enough to them and see the length of the head, that gives you the ability to determine the length of the individual so we get different size classes of the crocodiles that we spotlight.

"We do it three times a year so it gives us an idea of the population numbers of the size classes.

"We've been studying the populations of freshwater crocodiles in a couple of our parks since about 2011 but the spotlighting data was just giving us general population numbers pre-cane toads.

"We wanted to get more detailed information on demographics and site fidelity and basically increase the intensity of the survey."

She says they netted just under half of the population counted in a spotlighting survey at two discrete pools along the Lennard River.

They intend to analyse the data gathered over the coming wet season.

"[We are] trying to determine whether or not there's a specific portion of the population that's going to be impacted by the cane toads to a greater extent," she says.

"So that we can understand how best we can look at different management options once the cane toads have come through."

She says the Bunuba Rangers' assistance with the survey was invaluable.

"Freshwater crocodiles are quite important to them," she says.

"Having them along with us was really good to have that cultural aspect as well as the science that we brought."