Marks on the rays indicated they were likely caught in nets. Photo / Shane Kelly
Twenty rays potentially caught by fishers have been dumped at an Auckland bay, some with their tails chopped off, in what a marine scientist has called a "very cruel" act.
The Ministry for Primary Industries is investigating, and say the deaths could also have been caused by orca.
University of Auckland marine scientist Dr Shane Kelly came across the graveyard of stingrays and eagle rays on Saturday morning on a beach just south of Whakakaiwhara Point at Duder Regional Park, east of Auckland city.
Kelly and a team were out monitoring birds, and saw a bunch of black-backed gulls circling above the rays.
Kelly said they had been clearly caught by fishers, likely in nets, with visible marks on their bodies. Some had their tails chopped off.
However he was not sure if it would have been commercial or recreational fishers.
Commercial fishers are legally required to land and report any bycatch.
Kelly said sometimes if rays were caught in nets they could be difficult to remove safely due to their stingers.
However with proper management they should be able to be released without killing them.
"So to find 20 or more all dumped together is really not on. Some had their tails cut off - it is a very cruel practice."
Rays were not uncommon in the Hauraki Gulf.
They play vital roles in the ecosystem, feeding off all sorts of creatures on the seafloor, and in turn are an important food source for orca - which are commonly seen in the Gulf.
"They are just fantastic creatures, very inquisitive," Kelly said.
"While they are common, even so our fisheries are under enormous pressure and this is the sort of thing we want to be managing effectively if we want to address the issues facing the Gulf."
Kelly was the lead author of the State of the Gulf 2020 report, which painted a grim picture of fisheries on the verge of collapse and sediment-choked and polluted waterways in Auckland and Waikato's big blue backyard.