As hundreds of thousands of alewife from Lake Ontario have been spawning for the season, authorities say recent weather changes have caused a surge in dead fish along the Greater Toronto Area shoreline.
At Humber Bay Park West in south Etobicoke, nearby residents posted pictures and videos on social media of hundreds of dead fish near the park’s boat launch close to the base of Mimico Creek.
“I saw the videos. We’ve been getting lots of lots of inquiries coming in,” Rick Portiss, the Toronto and Region Conservation Authority (TRCA)’s senior manager of aquatic monitoring and management, told CityNews on Tuesday.
“We see it in varying degrees every year, and this seems to be a higher-than-[usual] … season.”
Portiss said the reports haven’t been restricted to the Humber Bay Park area, noting dead alewife fish have washed up at spots along Lake Ontario within, and next to, TRCA’s jurisdiction (which runs between the Toronto-Mississauga border and Ajax).
Alewife is a smaller, silver-coloured, non-native fish species that is found in great abundance in the deep waters of Lake Ontario. It is similar in appearance to smelt and related to herring. Portiss said alewife became an invasive species in the upper Great Lakes, which spread to the area during the construction of the Welland Canal system.
When asked what’s behind the recent surge of dead fish, Portiss said alewife come closer to shore during spawning season in search of shallower, warmer waters and where there are sandier areas (similar to fall salmon runs in the GTA). He said the fish in those spots are “very susceptible” to temperature changes.
“We had a storm last week, fairly significant with a lot of wind, and what it does is it brings up cold water from the deeper area. The fish are already acclimatized to the warm water where they came in to spawn, and then they get hit by a cold water upwelling, and it really affects the fish,” Portiss said.
“It tends to kill them or disorient them. That’s why people are seeing them spinning in circles and floating on their bellies and everything else in the area.”
Officials with the Ontario Ministry of Natural Resources echoed the observations shared by TRCA.
In a statement to CityNews, a spokesperson said every May and June brings similar die-offs. The spokesperson added that instances of dead fish can be reported to the ministry for monitoring.
Meanwhile, Portiss said the dead fish will act as a food source for wildlife and added most should end up being consumed.
