Wellington, Feb 18 NZPA - A special inshore Kaikoura fishing area should be axed after a commercial fisherman caught and killed a protected Hector's dolphin, a marine mammal expert says.

Set netting is banned in many areas where Hectors's dolphins and the critically-endangered Maui dolphin live, but the special Kaikoura area was negotiated by the Te Korowai Trust o Te Tai o Marokura to allow for commercial netting one nautical mile offshore around the Kaikoura Canyon.

An associate professor of zoology at Otago University, Professor Liz Slooten, said the Kaikoura fishing area should be abolished, and commercial nets banned within four nautical miles of the coast.

She said the Hector's dolphin drowned in a commercial gill net 1.3 nautical miles offshore, southeast of the Haumuri Bluffs, last May.

Prof Slooten said that area was a well-known hotspot for Hector's and dusky dolphins, and if Kaikoura had provided offered the same protection as the rest of the South Island's east coast, the Hector's dolphin would not have died.

Prof Slooten and Associate Professor Steve Dawson have published detailed analysis of the impact of the wider protection measures in the scientific journal Aquatic Conservation.

Threatened dolphin populations were still declining, they warned.

Prof Slooten said the protection measures put in place in 2008 by then-Fisheries Minister Jim Anderton were a step in the right direction, but too many areas had been left out of the protection package or been compromised in other ways.

"Tasman Bay, Golden Bay and Taranaki were left out and in other areas dolphins are declining because protection does not go far enough offshore," she said.

"This includes the west coast of the South Island, where dolphins are protected from entanglement in gill nets out to two nautical miles offshore for three months of the year, but Hector's dolphins there range to six nautical miles offshore, year round."

The Kaikoura exemption was made on the basis of claim that the deeper waters off Kaikoura were rarely used by Hector's dolphins, but the boundary was drawn far too close to shore.

"Simply too many compromises were made in the protection package."

Trust chairman John Nicholls told The Press that said the fishing area was to help sustain the local fishing industry, and the area was defined according to the best information at the time.

The trust would consider circumstances of the dolphin's death as it developed the marine-mammal section of its own coastline-management strategy, he told The Press.