Ontario study: climate change impacts freshwater fish range

Largemouth bass. Image: Ontario Ministry of Natural Resources.

Largemouth bass. Image: Ontario Ministry of Natural Resources.

“Fish gotta swim and birds gotta fly,” as the classic Broadway musical “Showboat” reminds us.

And new research in Ontario shows that climate change is affecting where some freshwater fish species gotta swim.

“Many fishes are now more likely to occur in lakes where climate was historically limiting,” said a recent study by scientists from University of Toronto Department of Ecology and Evolutionary Biology and the Ontario Ministry of Natural Resources. They analyzed contemporary and historical data for 1,527 lakes across the province.

The results provide “insight into the processes controlling species ranges and improves our ability to predict future range shifts,” the study said.

It focused on changes in the habitat range of six sportfish species — bluegill, largemouth bass, smallmouth bass, rock bass, brown bullhead and pumpkinseed — and seven baitfish species: blacknose shiner, bluntnose minnow, common shiner, creek chub, emerald shiner, golden shiner and northern redbelly dace.

The northern boundaries of sportfish species have moved further north in the past three decades, although the amount of change varied from species to species, according to the study published in the journal “Diversity and Distributions.”

Most of the species have moved in expected directions toward higher latitudes and elevations, according to the article.

In contrast, the northern boundaries for baitfish often shifted toward the south, also varying by species.

Karen Alofs, a post-doctoral researcher at the University of Toronto and the lead author, said it’s one of only a few studies of why the range of freshwater fish species is changing.

The study expresses no doubt about the existence of climate change, citing annual increases in mean air temperature for the past 40 years. Warming occurred in all seasons.

“The Great Lakes and Precambrian shield region, which spans most of Ontario, are warmer than it has been since at least the start of the last glaciation” – or Ice Age.

The shifts are occurring at rates comparable to what’s happening to plant and animal species in “marine and terrestrial ecosystems around the globe,” it said.

Alofs said, “In talking to the general public, they realize there are changes already happening in the distribution of species that are potentially related to climate, and we don’t understand yet how they will impact individual species and interaction between species.”

Natural dispersal isn’t the only reason for expansions in range, Alofs noted. “It’s likely some are due to human dispersal, some accidental, some deliberate. That’s probably been happening for a long time.”

For example, the study said species have spread to new territory in Ontario through stocking by natural resources agencies and by fish swimming through connected waterways. However, most “human-mediated” dispersals are unauthorized, such as bait-bucket transfers and “illegal introductions by anglers and lake residents.”

Human intervention alone isn’t enough to change the range of a species, the study said. “To extend their ranges northward, species must first disperse to new habitats and then establish self-sustaining, reproductive populations where they previously did not occur.”

And because many introductions are human-related, natural resource managers could potentially do more to control them, Alofs said.

The next step for researchers is to understand the impact of the changes, she said.

To illustrate, there is ongoing research about which species introductions are most likely to succeed. Do resident fish populations have an impact on the ability of the newcomers to survive? What impact do the newcomers have on the ability of native species to survive in light of competition for food and habitat? Will opportunities for recreational anglers change?

From a research perspective, she said the study also shows the importance of monitoring programs to understand changes across large geographic regions such as Ontario.

“This study wouldn’t be possible without the historical records that are available– data because of monitoring studies and museums allow us to see these changes over time,” she said.

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