Forest & Bird Otago-Southland regional conservation manager Chelsea McGaw said 207 adult sooty shearwaters (tītī) were captured near Te Waewae Bay between January 1 and March 31 — right in the middle of the bird’s breeding season.
While the birds did number in the millions, their numbers were declining and their nesting sites were considered a "critically endangered ecosystem" on mainland New Zealand.
There were four colonies of the birds on the mainland — one near Sandfly Bay, at Otago Peninsula (where 72 chicks fledged this year), one at St Clair, one at Long Point (Irahuka) in the Catlins and one in Bluff.
It was possible some of the birds caught were from a mainland site and a "high majority" of the birds caught by the fishing vessel would have had chicks in their nests at the time that now would have died as a result, Ms McGaw said.
The capture would have had "cascading effects" on colonies and captures such as this one needed to be avoided.
"When you're fishing, you're there to catch fish, right?
"And dragging out 207 seabirds, that's just insane to me.
"Just the fact that one single trawl has hauled up 207 seabirds in one go is pretty devastating."
It was "sobering" catches such as this were not illegal, as long as they were reported.
She called on the Ministry for Primary Industries (MPI) to urgently review and strengthen seabird bycatch mitigation in trawl fisheries.
"Unlike in surface longline fisheries, where international best practice (three out of three mitigation measures) is now in place, trawl fisheries still rely on inconsistent voluntary measures."
Fisheries New Zealand fisheries management director Emma Taylor said the bycatch had been included in MPI’s quarterly bycatch data.
A New Zealand-based commercial fishing vessel operating off the south coast of the South Island had reported the accidental catch of 207 sooty shearwaters in February.
The vessel was operating an onboard camera, and footage of the capture was reviewed by Fisheries New Zealand.
"The vessel was also using mitigation measures, including batch waste disposal during towing," she said.
"For your information, the total population of sooty shearwaters has been estimated to be about 21million birds.
"No fisher wants to catch seabirds, but it is not illegal to accidentally catch them."
The fisher took the steps required following the capture, reported the incident to Fisheries New Zealand and notified a Department of Conservation protected species liaison officer.
Fisheries New Zealand staff also met commercial fishers in the region to discuss the incident.
"We provided information about operational measures they could take to reduce the likelihood of further bycatch events in the area, including avoiding the area of the capture, and ensuring appropriate mitigation measures were being used."
Seafood New Zealand inshore general manager Tiff Bock said the industry body was concerned about the loss of birdlife.
"It is no exaggeration to say it has a serious impact on the fisher, who is really upset about what happened.
"We find ourselves agreeing with Forest & Bird that a one-off capture event like this is devastating.
"We hate to see birds harmed.
"In this case, we can reassure you that the fisher was doing everything he was supposed to be doing in terms of location and procedures to avoid bird interactions.
"The muttonbirds [tītī] congregated around the vessel en masse after the fishing gear was in the water, leaving him with nothing he could practically do."
Since the incident, Seafood New Zealand had organised an event to get all the local fishers together to discuss protecting seabirds and mammals "and they agreed to a range of measures including avoiding some areas", Ms Bock said.
The latest data from MPI showed 98% of the time a commercial net or line or other device was put in the water there was "no interaction with a protected marine mammal or bird".
