Dumped goldfish are reproducing and taking over Hamilton Harbour


Hamilton Harbour is being turned into a giant goldfish bowl, but environmental researchers aren’t happy about the region’s newfound pets.

According to reports, the nearly two million large and small goldfish that have been counted by researchers at the Royal Botanical Gardens (RBG) this year are likely descendants of people’s unwanted pets—unfortunately, the harbour isn’t a good home for them either. That’s because the orange and dull-grey fish are throwing yet another wrench into plans to rehabilitate the bay, which is also plagued with carp.

RBG and other organizations have been trying to tackle the harbour’s carp problem for years. Like goldfish, carp are an invasive species, which means that they’re not native to the location. According to Ontario’s Invading Species Awareness Program, without any natural predators or controls, invasive species can have devastating effects on native aquatic life, habitats, and ecosystems.

Carp are not only destructive because they crowd out other fish species, but also because they’re bottom feeders, which means they’re constantly churning up the soft sediments of rivermouth marsh environments in search of food, inhibiting the growth of plants and indigenous fish species as a result.

That’s why Becky Cudmore, an invasive species expert with Fisheries and Oceans Canada, is urging people not to release pet fish like these into the wild.

“They might think they are a doing a kind thing for the fish, but they are not doing a kind thing for the ecosystem,” she told The Hamilton Spectator.

So far, the goldfish are considered less harmful than carp, but when they become fully grown (potentially reaching more than 40 cm in length), researchers are concerned that they’ll be big enough to inflict similar damage on the already fragile ecosystem. That’s why the increasing prevalence of goldfish is so troubling.

“They seem to be heading toward taking over,” Tys Theysmeyer, head of natural lands for RBG, told The Spectator. “People used to actively release goldfish into the bay a lot,” he told CBC News. “In the last five years, their numbers have been rising and rising.”

While goldfish previously had very low survival rates in the wild, changing conditions have allowed them to reproduce with relative ease.

“With increased warming trends we’re seeing an increased ability of some fish species to survive in areas where we wouldn’t think they could survive,” Cudmore said.

Water levels have also played a part. Theysmeyer told The Spectator that low levels in early summer, which rose quite suddenly later on, assisted in the goldfishes’ ability to reproduce.

When the water levels jumped, Cootes Paradise—an area where fish tend to reproduce—”basically turned into a goldfish factory,” he said. This, combined with the poor water quality resulting from contaminated overflow from the city, have discouraged native species from flourishing, making even more room for goldfish.

But Cudmore says Hamilton Harbour isn’t the only place seeing this pattern—the problem has arisen at numerous locations in the lower Great Lakes, and the north shore of Lake Erie in particular. Hamilton Harbour just happens to be a hot spot.

According to CBC News, RBG has contacted the Department of Fisheries and Oceans and Ministry of Natural Resources to determine whether or not they want to take action, and if so, how to move forward.

The hope is that birds and bigger fish will utilize the plentitude of goldfish for food, which will help reestablish native fish populations such as pike and bass.