Nova Scotia

Striped bass mass death studied near Nova Scotia Power plant in Trenton

A new study investigating an unusual fish kill in Pictou Harbour, N.S., has found striped bass that congregate in warm waste water near the local power plant died of cold shock after the facility's turbines were shut down in the middle of winter.

Utility says it takes precautions to protect marine life around coal-fired plant near Pictou Harbour

Striped bass were reclassified from a threatened to endangered species in 2012 by the Committee on the Status of Endangered Wildlife in Canada. (Meghan Wilson/DFO)

A new study investigating an unusual fish kill in Pictou Harbour, N.S., has found striped bass that congregate in warm waste water near the local power plant died of cold shock after the facility's turbines were shut down in the middle of winter. 

Striped bass were reclassified from a threatened to endangered species in 2012 by the Committee on the Status of Endangered Wildlife in Canada. 

Nova Scotia scientists examined 98 dead striped bass that were collected in January 2013 near the Trenton power plant several days after a suspected mass death. 

Researcher Michael Dadswell, a retired Acadia University professor, said the cold-shock event that killed the fish likely didn't have a major impact on the population of striped bass.

But if striped bass have a low spawning season, he said die-offs from quick water temperature changes near the power station in winter can further endanger the population.

Not unusual fish behavior

Dadswell said striped bass populations fluctuate from highs to lows every 30 years and aren't the only species that collect near warmer outflows and experience cold shock.

"There's quite few studies that have been done on Lake Ontario, on the atomic power plants, where the fish are drawn to the warm water outflow," he said. 

The dead bass were found 700 metres from the Trenton coal-fired plant, operated by Nova Scotia Power at the mouth of the East River.

In an email, Nova Scotia Power spokeswoman Beverley Ware said the utility is aware bass "periodically congregate" near the plant. The company has "a screen in place that acts as a barrier to prevent the fish from getting past a certain part of the canal." 

Cold shock

Freshwater is drawn from the East River to cool down steam used to turn the Trenton plant's turbines.

The plant's regulated waste water is "returned to its source at a slightly elevated temperature," according to Nova Scotia Power's website.

The Acadia study published in March, however, found that water temperatures near the facility fell from 12 C to below zero in less than 24 hours when the plant's power turbines were turned off for three days in early January 2013. 

A recent study examined 98 dead striped bass that were collected in January 2013 near the Trenton power plant several days after a suspected mass death. (Google Maps)

Nova Scotia Power disputes the significance of those numbers. The listed temperatures aren't those of the outflow, Ware said, but rather the condenser temperatures inside the plant. 

"The water in the outfall does not abruptly cool down — it does not happen instantaneously," she said. "The warmer water from the plant would remain in the channel cooling slowly and there would still be a warmer area of water in the bay — also cooling to ambient.

"In essence, it sits there for a while and gradually cools down. Fish are very mobile so there's no certainty they would be there when this happens."

Proving the fish were there

Dadswell, however, said the researchers could tell that the fish had been in the warmer water before their deaths, based on what they ate.

"During the winter, bass don't feed very much because of the cold water. They basically sort of semi-hibernate," he said.

In the warm outflow, he said, "they were feeding on each other and feeding on small minnows that were also attracted to the area." 

For the first time, Dadswell said, the study helped prove that striped bass are cannibalistic like some other species. 

Young fish most susceptible

Striped bass only have one known spawning location, according to the Committee on the Status of Endangered Wildlife in Canada. They were deemed endangered after too much poaching, and recreational and commercial fishing. 

The Acadia study found that young and small bass were most at risk because they're smaller and can't withstand the cold shock as well as the larger adults.

The study stated it's difficult to know how many striped bass died in 2013 because the fish were collected several days after the suspected cold-shock event. Scavengers may have cut down on the number. 

Dadswell said the solution to the problem is simple.

"All they have to do is not turn it off in the winter, when it's cold." 

Ware said there's only been one instance in 10 years that Nova Scotia Power has turned off both turbines at the same time in the winter. The utility also conducted a study in 2014, she said, that found no evidence marine life had been impacted since 1991. 

ABOUT THE AUTHOR

David Irish

Reporter

David Irish is a producer and digital editor for CBC Nova Scotia. dave.irish@cbc.ca

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