A kangaroo pet food trial in Victoria found shooters were driven to slaughter more animals for profit and the program was beset by fraud and bribery offences, according to a state government report.

Since the trial began in 2014, there has been a 250% increase in the number of kangaroos killed in Victoria. One million died under the program.

The Department of Environment, Land, Water and Planning report was released under freedom of information to the Australian Society for Kangaroos.

Shooters were killing more kangaroos to maximise profits and were favouring male carcasses over females because the large size meant extra money, the report said.

“Current design and compliance arrangements are insufficient to manage the risks associated with the trial,” the report said.

The report warned of overshooting, shooters bribing landholders to access kangaroos, and farmers committing fraud and providing false and misleading information on applications. In one case, authorities are pursuing prosecution.

It said the costs to the state government running the trial have outweighed the calculated benefits over the trial period. Cost recovery arrangements should be a factor in a future program design, the report said.

The Australian Society for Kangaroos president, Nikki Sutterby, said it appeared that nearly half of Victoria’s kangaroos had been wiped out since the trial began just five years ago.

“Hundreds of thousands of little joeys have been brutally killed or orphaned as a result of this trial in Victoria,” Sutterby said.

She pointed to a 2014 study that found professional shooters in some cases had been observed swinging pouch joeys by their hind legs while bashing them against utility racks, stomping on their heads, and decapitating joeys without stunning.

The environment department insisted it had made changes to the program, including more frequent reporting protocols on the number of kangaroo carcasses processed and a crackdown on tags remaining on properties.

“The purpose of the trial is to reduce the waste of carcasses from kangaroos that would have been controlled, regardless of the trial,” the spokesman said. “The extension of the kangaroo pet food trial in 2018 allowed time to see whether changes to compliance, monitoring and education would address the issues that arose in the evaluation.”

The trial continues until the end of this month.