Tasmanian anti-duck hunting activists say they have been intimidated after a dead wallaby and bags of human urine were left around their campsite.

Chris Simcox and a small group of campaigners attempted to disrupt the first day of Tasmania’s official duck hunting season on Saturday at Moulting Lagoon Game Reserve on the state’s east coast.

The campaigners visited the lagoon early in the morning, speaking to shooters and attempting to scare ducks away from the area.

When they returned to their camp, they found a dead wallaby near their cars, and rubbish and bags of urine strewn around.

“We are just trying to give the ducks a fighting chance,” Simcox told Guardian Australia. “What we are doing is completely legal. We are abiding by directives issued by the police and by parks and wildlife staff.

“We set up on the Friday night, we camped overnight. We headed to the lagoon and came back mid-morning. We found a dead wallaby carcass near one of our vehicles, we found what looked like human urine, a little bit spread around and tipped on our camping gear. And a number of bags of rubbish tipped around, a few feed bags.”

Duck season is open in Tasmania between 9 March and 10 June this year. Five species can be legally hunted during that period: the Pacific black duck, chestnut teal, grey teal, mountain duck or shelduck and the Australian wood duck.

Victoria’s duck hunting season runs from 16 March to 19 May, and South Australia’s from 16 March to 30 June.

In January, the Victorian government announced that it would cut its season short by three weeks, after experts warned it would damage the long-term bird population, with waterbird numbers at their lowest point in 34 years.

On Saturday, Simcox said only “a small element” of the hunting group was responsible for the intimidation.

“I’ve been out here for about 13 years myself … we certainly haven’t had much issues with this sort of thing. We’ve come here, as we do every year during duck season, to stop the ducks being shot and give them some protection.

“At one point a fairly aggressive shooter approached and told us what we were doing was illegal, and said some expletives. I challenged him and said: ‘What’s illegal about it?’ He couldn’t tell me.

“The shooters nearest to us, we spoke to them, they were quite pleasant. They said they were concerned for us.”

Simcox said he and his group opposed duck hunting because it was cruel.

“It’s quite plain and simple – it’s quite cruel. If they shoot at ducks, there are invariable a number who get injured and don’t get retrieved.”

The Tasmanian government’s duck-hunting code of practice says: “Duck hunters often shoot more than one duck from a group before retrieving the carcasses. This is acceptable provided that where an individual bird is wounded no further animals are shot until all reasonable efforts have been made to dispatch the wounded bird as quickly and humanely as possible.”