Five New Zealand sea lions have died so far this year after being captured in squid fishing nets around the Auckland Islands.

NZ sea lions are a critically endangered species.

Fisheries NZ released data today on "captures" since January 1, based on reports of its observers on squid boats.

It is the third day in a row on which government officials have confirmed deaths of endangered animals in fishing operations.

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On Monday, Fisheries NZ said four Hector's dolphins had been caught and died during trawl fishing off the east coast of the South Island in December.

Yesterday, Conservation Minister Eugenie Sage said five Antipodean albatrosses and one Gibson's albatross died after they were caught by a longline fishing boat off the Bay of Plenty between early December and last month.

Forest and Bird said the sea lions listed as "captures" by Fisheries NZ had all died. Four of the deaths were last week.

"Four endangered sea lions in a single week, five so far this year, is sickening and totally preventable," said the conservation organisation's ocean advocate, Katrina Goddard.

"Commercial trawlers should not be fishing in the same patch of water an endangered animal lives and breeds in.

"There is no way anyone would be allowed to accidentally kill four kiwi in the course of making a profit, so why are commercial fishers allowed to kill endangered native animals?"

Sanford spokeswoman Fiona MacMillan said the fishing company was shocked by the spate of sea lion captures and consequently it had taken "extraordinary" actions.

"When the five captures happened in quick succession, we pulled all Sanford vessels out of the entire fishing area, regardless of whether they had captured a sea lion or not, while we assessed the situation."

"Four of the deaths were from one vessel and we are taking an ultra-cautious approach by continuing to keep that vessel out of the fishery."

"On every occasion a sea mammal watch was carried out before the fishing gear was deployed. The vessels in the area were all using sea lion exclusion devices, a kind of escape hatch to let sea lions out of fishing nets."

"We are committed to sustainable fishing. Our ethos is to catch fish sustainably without harming endangered species. That is why we are taking this so seriously."

Sage said of the bird deaths: "Antipodean and Gibson's albatrosses are as endangered as kākāpō. We must do all that we can to protect them."

She said the bird bycatch had occurred even though the fishing boat was complying with regulations for reducing bycatch. The industry needed to go further and adopt innovations such as hook-shielding devices for surface long-lining.

Fisheries NZ's squid fishery observers reported that the boats were complying with the regulations and were correctly using the exclusion devices in their nets at the time of the captures.

"It is not illegal to catch a sea lion, however it is a legal requirement to report any captures."

The agency contrasted the five sea lion captures this year - the season runs until June - with estimates of 70 to 140 a year a decade ago.

"Sea lion deaths have substantially reduced over the last decade since all squid trawlers have fitted approved sea lion exclusion devices in their nets."

The agency's director of fisheries management, Stuart Anderson, said the five captures since the start of the season last month was incredibly disappointing.

"Catching five sea lions this early in a season is unusual."

"By comparison, last season two sea lions were captured in the whole season, and the season before there were three captures."

Anderson said fishing was just one of a number of threats faced by sea lions. The main one was disease.

The agency said the Auckland islands, lying almost 500km south of the South Island, are home to the largest breeding colony of New Zealand sea lions, comprising around 70 per cent of the total sea lion population of over 12,000.

The Seafood NZ industry association said in response to the seabird death data, "We are committed to mitigating our impact. The seafood industry is actively engaged in seabird management groups including the Antipodean action group and Black Petrel Working Group and is working on a number of projects, including ... deploying 1800 hookpods on the surface longline fleet as part of a feasibility trial ..."