Is Climate Change Really Making Fish Bigger? A New Study Says Yes
When researchers studied a dozen species of salmonids, including brook trout, they expected smaller sizes due to warming water temperatures. They found the opposite
If science’s worst predictions about the effects of climate change prove true, then it seem the apocalypse may arrive a little ahead of schedule, with melting glaciers, record drought, wildfires, and mass extinctions. But if you’re a glass-half-full kind of person, and an angler, you can take heart in knowing that some fish will be bigger, according to a new study from the University of Wisconsin-Madison.
The idea that climate change is producing monster fish—despite predictions that it would make them smaller—has been in the news lately, or at least in the headlines. When you read a little deeper into most of these stories, however, you learn that temperature changes aren’t actually making fish grow larger but rather prompting big fish to relocate in unexpected places, causing a splash.
This latest study is different. According to findings published in the journal Global Change Biology, several species of salmonids, including Arctic grayling, brook trout, and lake trout, are actually growing bigger as a result of climate change—exactly the opposite of what the researchers anticipated.
“One widely expected result of global warming is that animal body size is going to go down,” said Olaf Jensen, an associate professor at the University of Wisconsin–Madison’s Center for Limnology, in a press release. The reason for this is Bergman’s Rule, something many hunters are familiar with, as it explains why whitetail deer, for example, are so small in Florida and so big in Saskatchewan. The rule states that individuals of a particular species tend to have more body mass in colder environments to better retain body heat.
So, with water temperatures warming due to climate change, researchers expected fish to get smaller. And yet, after studying decades of long-term data on 12 salmonid species in warming climates around the world, they found that eight of the dozen species not only didn’t shrink, they showed significant increases in length.
“I think the main take-home message from this study is that we cannot assume that the effects of climate change are predictable and negative,” said Mary Solokas, the paper’s lead author. In colder parts of the globe, where the study’s salmonids live and where, despite warming, water temperatures remain below the species’ optimal levels, climate change may simply be creating longer growing seasons, as well more plankton, plants, and invertebrates for these fish to feed on and grow larger.
The bad news, according to the study’s authors, is that continued warming could push water temperatures past optimal levels for these fish and ultimately lead to stunted growth rates and susceptibility to disease. In other words, if the worst predictions do come to pass, maybe move north for the bigger fish, before it’s too late.