Miserable winter killed farmed salmon
In the early days of salmon farming in British Columbia is wasn’t unusual for fish harvesting crews to use seawater with added salt and ice to create a slurry that was used to stun the farmed salmon prior to bleeding and subsequent processing. The fish would typically be dip-netted out of a net pen and into plastic totes containing the prepared chilled and salted seawater, where the fish would soon slow down and eventually become lethargic enough to be handled by the crew. If one left a fish in this slurry too long, the fish would be as stiff as a board. The advantages of using this stunning method were low cost and an immediate chilling of the fish which would contribute to the high quality of the farmed salmon.
Due to extreme temperatures, high tides which adds to the chilling of the in-coming seawater following a low tide, fish in farms on Canada’s east coast have been known to succumb to this phenomenon, although as Wikipedia explains, this should not be referred to as “superchill” or “supercooling”:“Supercooling is often confused with freezing-point depression. Supercooling is the cooling of a liquid below its freezing point without it becoming solid (usually due to the lack of a seed crystal or nucleus- Ed. note). Freezing point depression is when a solution can be cooled below the freezing point of the corresponding pure liquid due to the presence of the solute; an example of this is the freezing point depression that occurs when sodium chloride(salt) is added to pure water”.
This condition has occurred in New Brunswick farms in previous years, and as Josh Pennell of The Telegram explains in a recent article, the weather this past winter has taken its toll on the farmed salmon of the Newfoundland province’s aquaculture industry;
The numbers aren’t in yet and the hope is that the losses won’t be drastic, but a percentage of farmed salmon fell victim to winter mortality. “This is an exceptional year,” says Miranda Pryor, executive director of the Newfoundland Aquaculture Industry Association (NAIA). “The environmental conditions and the water temperatures are the coldest we’ve seen in well over 10 years.” The fish die in what’s called a super chill event. If the fish hit a critical temperature, they can’t survive, Pryor says. It’s a rare event that hasn’t happened here in quite some time.
Rare, but not abnormal, Pryor says. The reason it isn’t known how many fish have been lost due to the super chill is that aquaculturists are still getting out to their fish cages and cleaning them up after the long winter. Normally they get out there every week, Pryor says, but when the water temperature is as cold as it was during this winter, they have to leave the fish alone. The salmon stay at a depth that has a preferred temperature. “If we disturb them, then they would tend to swim into areas of the cage which may be colder.”
That can lead to massive mortality. So the fish farmers haven’t been out to their cages in months in some instances and are just now getting a handle on what they’ve lost. Dead fish from the aquaculture industry had been going to a local compost company. That company is being restructured and so that’s no longer an option. Other times — the least preferred option, Pryor says — the dead salmon are sent to the landfill. The winter mortalities being collected now are sent to the Barry Group facility in Burgeo to be rendered into a fish meal product. Pryor says they’re hoping to get the final numbers on this winter’s farmed salmon mortality in a few weeks.
