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'Superchill' kills fish at Cooke Aquaculture sites in Nova Scotia

A technician holds a salmon from a fish farm.
A technician holds a salmon from a fish farm.

SHELBURNE - Cold weather caused a large number of fish deaths for Cooke Aquaculture in Nova Scotia last week.  

A technician holds a salmon from a fish farm.

Three aquaculture sites are reporting fish mortalities from extreme cold water temperatures -the Port Wade aquaculture sites in the Annapolis Basin, Shelburne Harbour and Jordan Bay.      

"A department fish health veterinarian has visited the sites in Port Wade and Shelburne and will visit the Jordan Bay site in the next few days to investigate the expected cause of death," said Fisheries and Aquaculture Minister Keith Colwell. "Our provincial fish health veterinarians investigate mortality events to rule out diseases of concern."  

A preliminary investigation found that a superchill happened.

Most winters, Nova Scotia's marine waters stay above freezing. Sustained cold air temperatures can drop the water below 0 Celsius, to the temperature that fish blood freezes, around -0.7 C.

Tides in late February and early March also tend to be high, and contribute to lowering temperatures in sea cages by flooding more shallow areas than usual. Low air temperatures cool the water and receding tides flush the cages with superchilled water.

Provincial officials say these types of events happen every five to seven years.

Cooke Aquaculture spokesperson Nell Halse said the company was still determining the scope of the loss, which was significant enough to see a vessel called in from another area to assist.

Halse said despite the “higher than normal mortality” the majority of their fish remained in good health and would soon reach harvest size.

She also noted that water temperatures had begun to rise in the region.

Provincial officials said the deaths do not pose any risk to the environment and that the company was properly disposing of the dead fish.

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