Why are so many dead fish washing ashore at Lake Erie beaches?

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Visitors to Lake Erie beaches have been puzzled by a flood of dead fish – particularly sheepshead, also known as freshwater drum – with thousands washing ashore in areas near Port Bruce and Port Stanley.

“The entire beach was littered with dead sheepshead,” on Monday, a Facebook user going by Cindy Disbrowe posted to the Port Stanley Bulletin page after she had been for beach walk in Port Bruce, located 50 kilometres southeast of London.

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Sheepshead are a humpbacked freshwater fish which are bottom feeders and considered a nuisance fish by anglers, according to Nature Conservancy Canada.

Commenters on Disbrowe’s post said the phenomenon also was visible in Port Stanley during the past week where hundreds of dead sheepshead were seen, as well as perch and birds along the bluffs and shorelines.

“At the shore about every metre there was a big healthy looking sheepshead,” said another online poster on the Port Stanley Bulletin. “It was the whole length of the beach.”

Central Elgin administration did not respond to a request for comment.

The deaths have not just been limited to the north side of the lake. Hundreds of freshwater drum  also were being found dead on the coastline near Erie, Penn., in mid-August, according to U.S. journal Erie Times-News.

Before they perished, the fish, it reported, were “doing a sidestroke and unable to right themselves.”

U.S. park workers gathered up the dead fish using pitch forks so beaches still could be used.

Earlier this year, a weather watcher who monitors severe storms on Lake Erie sounded the alarm about what he said was shaping up to be a potentially destructive year ahead on the lake.

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Lake Erie is the southernmost and shallowest of all the Great Lakes.

Rick O’Banion, who tweets as Storm Watch-Lake Erie on X, said he was worried the lack of ice on the lake last winter, combined with global weather patterns, could lead to massive fish die-offs, among other things.

But that may not be what is happening.

Michael McKay, executive director of the Great Lakes Institute for Environmental Research at the University of Windsor, said the die-off is “something frequently related to thermal stress” or what is known as an upwelling in hypoxic areas.

Hypoxic zones are a deep area of the lake “with very little dissolved oxygen,” according to the U.S. research foundation known as Oceanic and Atmospheric Research.

During an extreme upwelling event, the lower layer of water – which is typically cooler than the water above it – is forced close to the shoreline by a wind pushing surface water away from the shore.

Ann Marie Gorman, a fisheries biology supervisor at the Fairport Fisheries Research Station in Fairport Harbor, Ohio, said the Canadian event “absolutely sounds like it is from an upwelling.

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“Freshwater drum tend to be the most common species that we see impacted lately,” she said.

“Essentially it suffocated the fish that were not able to avoid it,” Gorman said.

“Fish kills due to hypoxic upwelling events usually occur every few years, but the conditions that lead to these kills are present every summer,” she said.

An upwelling event is usually accompanied by a strong odour of decay from the decomposing carcasses on the shoreline, Gorman said.

“Hungry wildlife in the forms of scavengers . . .  will help clean up the dead or dying fish, so natural events like these make some wildlife very happy,” she said.

According to the Journal of Great Lakes Research, globally the number of marine hypoxic zones has doubled each decade since the 1960s.

In 2018, they numbered more than 400, it said.

hrviers@postmedia.com

@HeatheratLFP

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