Biometrics gave up the goat numbers

The latest report on a startling rise in the Western Division feral goat population, to number 2.5 million in 2010, is available thanks to a largely hidden science – biometrics. 

Commissioned by the Western Catchment Management Authority (CMA), NSW Department of Primary Industries (DPI) researchers produced scientific evidence to show that feral goat numbers have grown four-fold in the last two decades. 

NSW DPI research biometrician at the Trangie Agricultural Research Centre, Gavin Melville, said it was thanks to a biometric formula that researchers were able to put a firm figure on the number of goats in the 450,000 square kilometre Western Division. 

“Our staff conduct aerial surveys from helicopters and fixed wing aircraft to monitor feral animals,” Dr Melville said.  

“The raw aerial counts nearly always underestimate the actual animal populations– it’s just not possible for observers in the aircraft to count every animal and that’s where biometrics comes to the fore. 

“We use a technique called mark-recapture, which applies statistical probability models on raw data from the aerial surveys, to get the most accurate estimates of animal numbers. 

“Our figures showed that between 1992 and 2010 feral goat numbers rocketed from 1.4 goats to 6.2 goats per square kilometre.” 

Dr Melville said these statistics will be used to better inform feral goat management. 

“Accurate figures help describe the real situation - effective management relies on using the best available data,” he said.

“We have designed a special protocol with two observers using a grid pattern which cross-references every observation.  

“Animal numbers are recorded in groups using on-board computer loggers which also record GPS locations, time of day and aircraft height and speed.” 

“At the completion of the survey all observations are reconciled to determine whether the front, rear, or both observers detected each animal group and it’s then we apply the mark-recapture technique to deliver accurate figures.” 

Results from the aerial surveys are used by NSW DPI, CMAs and the NSW National Parks and Wildlife Service to manage pest animals, measure their impact and quantify control programs.