According to a release from the department, Mowi site “AQ#1135 site (The Gorge),” which is located off the southern coast of Newfoundland, had 92,700 fish die out of a total of 900,000 at the site. Due to the amount being higher than 10 percent of the total, the mortality was required to be publicly reported.
The mortality was caused by sudden low dissolved oxygen levels at the site, the department said. The fish were roughly 3 kilograms, and were scheduled for harvest before the end of the year.
“We cannot speculate on the exact cause for low dissolved oxygen at this time, however, lower dissolved oxygen levels are generally associated with higher summer water temperatures and abundance of plankton,” Mowi Director of Communications Ian Roberts told SeafoodSource
Marine Harvest Atlantic Canada said in a release that the company will investigate the exact cause of the die-off.
“Further study is underway to determine causation of the low dissolved oxygen and develop further mitigation strategies to prevent recurrence,” the company said.
The department added that Marine Harvest Atlantic Canada has been “fully transparent and cooperative” as the department continues to monitor the incident.
“Under oversight of the department, the company is taking all responsible steps to address the incident. Mitigation measures required by the department include deeper nets and aeration equipment at the site and mortality removal has commenced,” the department said.
The deaths mark the second Atlantic salmon mass-mortality incident in the Northwest Atlantic Ocean related to low oxygen levels in a month. Cooke Aquaculture announced in late August that its farm sites located off Black Island, near the town of Frenchboro, Maine, U.S., had salmon mortalities related to “uncommonly low oxygen levels” in its cages, though the exact number of salmon killed by the low oxygen was not disclosed.