Southern rock lobsters pulled up in pots in coastal waters off the southern South Island — in the grip of a marine heatwave since November — have been described as lethargic.
Their shells have been described as thin, soft, or weak.
CRA8 Rock Lobster Industry Association chief executive Malcolm Lawson said he was worried heat-stressed lobsters, which usually would shed and regrow their shells just once in a season, could be going through a second moult induced by the above-normal sea temperatures of marine heatwaves.
There were industry concerns it could affect the quality of the product now in high demand in the lucrative Chinese market.
Mr Lawson, whose CRA8 quota management area covers South Westland, Fiordland, Stewart Island and around to the Catlins, said it was the second successive year the phenomenon had been observed in the lobsters.
Last year, a marine heatwave in Fiordland reached great depths and caused widespread bleaching of sea sponge and about that time lobsters were first seen to be affected as well.
"We simply had no idea what was causing it."
Mr Lawson’s concerns led him to conversations with University of Otago scientists, including those tracking marine heatwaves as part of the Moana Project.
In Tasmania, a recent major marine heatwave spurred similar observations in the industry where it had been put down to a second moult, he said.
He did not believe it would be fatal to the stock, but the CRA8 area alone accounted for nearly half of New Zealand’s lobster production.
The Chinese market was prepared to pay premium prices for New Zealand rock lobster, "but the other side of that is that they expect the product to be of top quality".
University of Otago marine scientist Gaya Gnanalingam, who is working with the industry to collect samples in the CRA8 area, said
to determine whether the animals were undergoing a second moult would require researchers to hold the animals for a longer period of time than her present research allowed.
However, a lot of lobsters’ physiological processes were influenced by water temperature, Dr Gnanalingam said.
Sea temperature changes could have a whole range of effects on the animals’ physiology, as well as their behaviour, she said.
"We might be seeing effects on the adults through the fishery, but they have quite a complex life cycle and so they’re larvae for a long time and then juveniles for a long time before they eventually get to the adult stage, and so their vulnerability to environmental pressures changes relative to their life stage as well," she said.
Fiordland Marine Guardians chairwoman Rebecca McLeod said the observations by the industry were "incredibly concerning" and it was important for marine ecosystems to remain healthy and intact, and therefore resilient to stress.
Regulating overfishing and keeping invasive pests out of the area were important but marine heatwaves were "obviously a way bigger problem than anything that we can tackle", Dr McLeod said.
"I don’t think we realised how soon we were going to be facing these consequences ... It just has really snuck up on us."
