A massive salmon die-off at Northern Harvest Sea Farms in Newfoundland claimed 2.6 million fish, and has environmental activists calling for closer scrutiny of the company’s proposals to expand.

The company owned by Norwegian aquaculture group Mowi said the losses, tied to abnormally warm water temperatures in late August and early September, killed almost half the stock in its Fortune Bay pens; some 2 million fish in the initial bout, and 600,000 more in the days that followed.

On Wednesday the Atlantic Salmon Federation called on Derrick Bragg, environment minister for Newfoundland and Labrador, to repeat an environmental assessment of Mowi’s plans to expand its Indian Head hatchery operations.

“Documents show Mowi is planning to add 2.2 million additional salmon into its existing sea-cages on the south coast of Newfoundland,” said Dr. Steve Sutton, ASF director of community engagement, in a prepared statement. “This means stocking more fish in the same area, even the same cages, affected by the recent mass mortality event, and doing so without any public environmental assessment.”

Mowi’s sea cages contributed to the die-off because they did not allow salmon to dive to cooler waters, company officials admitted. The even affected 72 of the farm’s 166 cages around 10 sites.

The company’s proposed $60 million Indian Head investment was approved by authorities in September 2018 over objections from environmental groups, who appealed that decision to the courts in April.

Mark Lane, executive director of the Newfoundland Aquaculture Industries Association, said activists are trying to delay the project and that starting a new assessment process would be redundant.

"What I think they're asking for is a repeat of environmental assessments on already approved sites, which really doesn't make a whole lot of sense. I'm not sure what you would achieve by doing that," Lane told CBC News.

Sutton of the salmon federation said the Mowi situation is similar to another project proposed in Placentia Bay where his group went to court and forced an environmental assessment. In that case, “it was a requirement for the hatchery and sea cages to be described together, and despite the repeated efforts of the provincial government to avoid a full environmental assessment, the court ordered it, calling it nothing less than ‘a duty owed to the people of the province.’ ” he said.

The die-off and the aftermath of cleanup raised a furor in Newfoundland, where pink sludge and odors fouled the water and air and critics complained farm operators failed to adequately communicate. Authorities suspended licenses for 11 of Mowi’s 13 operations, and Northern Harvest Sea Farms managing director Jamie Gaskill was contrite in an Oct. 11 statement.

“We of course accept the decision, and we are committed to satisfying those conditions once we receive them,” said Gaskill. I want to state for the record that we should have advised earlier of these additional mortalities as they occurred over time. I take responsibility for this personally as the managing director of the company. We were too focused on clean up efforts, and we have learned from this experience.”