Salmon in open-net pens operated by Mowi Canada East's Northern Harvest Sea Farms began dying in large numbers earlier this month, sparking debate over the how well Newfoundland and Labrador is regulating its burgeoning aquaculture industry.

Mowi has not disclosed the number of fish that died in September. Jason Card, the company's director of communications for the province, told IntraFish the information is still being collected.

He said the die-off was due to pro-longed high water temperatures at some sea sites on the south coast of Newfoundland, and that the company's decades-old gear is not up to the challenge of combating climate change.

"We're not assuming this temperature spike we experienced is a one-off, we're treating it as a new normal," he said.

The biggest updates will be creating deeper nets and aeration systems, he added.

The high temperatures created low oxygen conditions that resulted in fish mortalities, according to Card. The company has since removed the dead fish and has harvested the remaining at the impacted sea sites.

"Northern Harvest’s continuous fish health monitoring protocols made it possible to take immediate action as soon as the issue was observed, and there was no loss of containment," he said.

Card also noted the mortalities pose no harm to humans, the environment, nor other fish or shellfish species.

Northern Harvest reported the matter to the NL government when it was observed in early September, and kept local mayors, Indigenous leaders, employees, and the Fish, Food and Allied Workers (FFAW) appraised of the situation, he added.

"Much as in agriculture, where frost and drought can impact crops, so too in aquaculture can fish be affected by environmental events like superchill and high water temperatures," he said. "We, like other farmers, are accustomed to dealing with the effects of climate change and will continue to adapt to the changing environment."