October 2, 2019

Warmer waters blamed for mass salmon deaths in Canada's Newfoundland

Warmer-than-usual water - and not sea lice - is the cause of death of farmed Atlantic salmons on the south coast of Canada's Newfoundland, said the province's chief aquaculture veterinarian.

Over 11 to 13 days, warmer water induced a drop in oxygen levels, leading to the deaths.  Previously, fish plant workers and Newfoundland's fish harvesters union posited that sea lice are behind the deaths of fish at a Northern Harvest Sea Farms facility.


However, veterinarian Daryl Whelan rejected the assumption.


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


He explained that the fish have nowhere to escape the heat as the entire water column experiences temperatures ranging from 18C to 21C.


Salmons that are raised in open net pens like those in the Coast of Bays-Fortune Bay area on Newfoundland's south coast started to die in August due to high water temperatures, said Northern Harvest Sea Farms.


"They will try and go to the cooler part of a net or a cage system," Whelan said, in effect bunching up at the bottom of the sea cage. If too many go down for too long, he said, it exacerbates the problem.


The recent fish deaths has led to Northern Harvest Sea Farms considering a redesign of its salmon cages, said Jason Card, a spokesperson for the company.


"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. 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," Card added.


The warm-water event was confined to the areas Northern Harvest is operating in, and no other aquaculture companies have reported any mortalities related to warmer-than-average water, Whelan said.


Temperatures on the south coast usually fluctuate, and wind and currents generally prevent the water from staying too warm for an extended period, he said.


"Each of our bays are entirely different and right now, all those bays are separated in that region, there's company by company," Whelan said.


"The other companies would be in different regions so there would be a different temperature profile."


The Canadian government was first made aware of the salmon deaths on September 2, according to Card.


Provincial fisheries minister Gerry Byrne said in late September that the potential number of affected fish could have been up to two million, but that not all of the salmons in the affected pens died.