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Warm water blamed for Newfoundland salmon mortalities

Atlantic Salmon Sea lice Water quality +5 more

The mass salmon mortalities that took place at a Northern Harvest salmon site in Newfoundland in September have been attributed to unusually high water temperatures.

Although speculation about the possibility of elevated sea lice numbers surrounded the event, which took place in early September, the province’s chief aquaculture vet has declared that nearly two weeks in which the water levels were between 18°C and 21°C at the end of August and early September led to low oxygen levels, which was the ultimate cause of the deaths.

"We've done the diagnostics and really, what's occurred is not an infectious process that led them to the mortality," Whelan told CBC. "What's led them to the mortality is the really low oxygen availability to them."

Northern Harvest, which is owned by Mowi, has not yet disclosed the number of mortalities caused by the conditions. It is, however, now looking at ways to redesign its salmon cages in a way that allows the fish to cope with elevated water temperatures, most likely by increasing their depth to allow the fish to drop into cooler water when required, as well as installing oxygenation systems.

"We have to act as though this temperature spike is not an isolated incident. We have to accept it as a new normal so that we are ready to deal with it," Jason Card, a spokesperson for the company, told CBC.

"So deeper cages, aeration systems, these are different ways that we can keep the water oxygenated, keep the fish cool and keep a good product going."