"Nobody wants to catch dolphins, common or otherwise, and fishermen ... feel gutted about this sort of thing," he said. "It's the last thing that they want in their nets."
He said trawlers move away "as soon as dolphin are seen," and the industry is committed to trying to avoid such events.
The government is due to release options for ways to further protect Maui's and Hector's dolphins, part of its response to conservation groups' demands.
About 214 international environmental and animal protection bodies urged New Zealand in a letter Wednesday to give "full protection" to the endangered Hector's and Maui's dolphins to prevent their extinction.
"Maui's dolphins, the world's smallest dolphin, are one of the rarest animals on earth and Hector's dolphins are almost as scarce as tigers," Care for the Wild International's Chief Executive Barbara Maas wrote in the letter.
Conservationists already have warned that even the best of the proposals will give the endangered dolphins only a 50-50 chance of recovering to their original numbers by 2050.
While many fishing boats obeyed the voluntary code of practice, it only took one or two who did not to wipe out the fragile species, Howe said.
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