For years, Andrew Murray would see small flocks of goldfish living in a lake with storms near his home on the outskirts of London, Ont. He had never thought much of them until this spring, on a sunny day in April, when the greenish pond was usually unusual, if not slightly orange.
A passionate nature photographer, he shot several close-ups. It wasn’t until he got home and looked at the pictures that he realized how many goldfish had to swim there.
“When I looked at them on my computer later, it was clear that there were thousands and thousands of fish there.”
Researchers at the University of Toronto believe this scenario is repeated hundreds of times in suburban storm lakes across the province. Originally built to reduce flooding in the neighborhood and ease the pressure on Ontario’s urban sewer systems, these pools have become zero for what Nicholas Mandrak calls “super invaders.”
Lakes zero for an invasion of goldfish
“What we’re seeing is the spread of goldfish in the suburbs of southern Ontario, actually in Canada,” said a professor at the University of Toronto’s Scarborough, who is studying freshwater conservation.
WATCH Prof. Nicholas Mandrak discusses the possible link between a wild goldfish explosion in Ontario and climate change:
Ontario’s wild goldfish population is exploding and climate change may be to blame
Professor Nicholas Mandrak of the University of Toronto’s Scarborough is discussing whether a recent explosion in Ontario’s wild goldfish population is linked to climate change. 1:18
With invasions reported in Alberta, British Columbia, Saskatchewan, Manitoba and the United States, goldfish are fast becoming one of the most prolific invasive species in North America. The reason they are so widespread is very much based on how people think about goldfish: harmless and disposable.
“People who put goldfish in city lakes may think they’re doing a good thing, ‘I’m not killing a creature,'” Mandrak said. “There should be no fish in these urban lakes.”
Once introduced into a storm pond, the goldfish begins to feed on the insects that usually colonize it. They reproduce rapidly, and their numbers, combined with their wide appetite, mean that they compete with amphibians and other creatures, reducing the diversity of native species.
They also flee when lakes are flooded, releasing fish into wetlands, streams, rivers and lakes, where Mandrak said goldfish become predators by eating the eggs and young of other fish.
Rare native species endangered by goldfish
Goldfish also take root, almost like an aquatic version of a pig, destroying habitats by uprooting plants and obscuring water for rare and endangered native species such as the prickly tortoise with soft shell, green arrow and rainbow clam.
Wild goldfish are out of control in this pond. I wonder what they eat. pic.twitter.com/yX6xs6JdjR
– @ armurray1
The gold diggers have been in Ontario’s wild waters since the 19th century, according to Mandrak. What has changed, however, is the sheer number of them, and he said this is probably due to the recent addition of suburban rainwater lakes and changing climates, offering fish more favorable conditions to thrive.
“It is only recently that they are becoming more abundant,” Mandrak said. “It’s largely because of these urban lakes.
“We also believe that climate change is involved. The waters of the Great Lakes and city lakes are warming more than before. The water seems to be more suitable for goldfish.
“As conditions become more extreme, that is, water that is warm and low in oxygen, one of the few fish that really does well in this type of habitat is the goldfish.”
The link with climate change
That is why Mandrak believes that goldfish deserve our attention. Not only are we releasing them into the wild, but man-made climate change is creating conditions for them to thrive through warmer water and spread to nearby wetlands through floods caused by more intense rainfall.
Climate change is causing suburban rainwater lakes to contain warmer water with lower oxygen content, conditions that allow goldfish to thrive while other species die. (Cole Burston / University of Toronto Scarborough)
That’s why goldfish are found in increasing numbers in Ontario’s protected wetlands, from Westminster Lakes in London to Cootes Paradise in Burlington.
“There are a growing number of goldfish and I really think this is climate change,” Mandrak said.
“We are seeing small annual increases in average annual temperatures, leading to a much larger and disproportionately larger increase in the number of goldfish, because climate change is causing these more extreme environments.”
Part of Mandrak’s research also includes an attempt to chart the life cycle of goldfish infestation in storm lakes, that is, how many generations it takes for fish to take over a body of water.
Scientists can determine the time that a goldfish infestation has been in a body of water by the size of its largest fish, which is known to grow to the size of a two-liter bottle, unlimited by the size of their bowls. and weigh up to two kilograms.
“Last year we took samples from a pond measuring 100 by 100 meters and containing approximately 20,000 goldfish,” Mandrak said. “We decided they had been there for between five and 10 years.
Add Comment