By Adam Hinterthuer – A new study has found that, when it comes to our freshwater fisheries, recreational anglers currently have a greater impact on fish populations than climate change. And that may be good news, says the study’s lead author, Luoliang Xu, because, faced with warming waters around the world, “local fishery management becomes a very important tool we can use to reverse the decline in these populations.”
The study, published October 1st in the journal Science Advances, was made possible by what the researchers call an “amazing” dataset of population trends and angler harvests for 521 different populations of fish across the Midwestern U.S.
The dataset was compiled by researchers at the University of Minnesota and the U.S. Geological Survey and consisted mainly of warm-water species, like bass and bluegill, and cool-water species like walleye and northern pike. Ninety-eight percent of the fish populations studied were living in lakes that are getting significantly warmer.
“Our original goal of this project was not really comparing the impact of fishing versus warming,” says Xu, who is a postdoctoral researcher at the University of Wisconsin-Madison’s Center for Limnology. However the data quickly revealed that the populations the researchers hoped to study are already impacted by fishing and if the team didn’t separate the two drivers, they “could never really understand the true impact of warming.”
Xu and his team combed through in-the-field data collected by state departments of natural resources, Tribal fisheries officials and even anglers themselves, who participated in creel surveys at boat launches and shoreline fishing spots. They then ran computer simulations that projected what the 521 different fish populations would look like with no warming and then ran simulations in which fishing was removed from the equation.
Their results showed that two-thirds of the warm-water species of fish were taking advantage of new warm-water conditions, with their populations growing. Meanwhile, just over half of the cool-water species were responding negatively to climate change and showing population declines.
But, despite the impact of warming waters on our fisheries, Xu says,“the catch from recreational fishing is a more important driver [of population trends]” In fact, of the populations they studied, “only one percent showed that warming was a more important driver than fishing.”
That means that, ninety nine times out of a hundred, the fate of a freshwater fishery was tied to the amount of harvest of fish from anglers.
Xu points out that much of their data comes from lakes that are heavily fished, so the fact that fishing plays a role in population dynamics is to be expected, still, he says, the overwhelming impact fishing has compared to warming was “surprising.”
“When you think of fishing in lakes, you think of a kid with a rod and a bobber. How can that be anything less than idyllic?” says Olaf Jensen, a co-author on the study and a professor at the Center for Limnology. But this study shows that recreational fishing is a powerful force acting upon our fisheries.
That doesn’t mean that it has to be a negative force, Jensen notes. When anglers caught more fish in a lake than the population could replace through reproduction, the numbers obviously went down. But, just as important, when fishing pressure eased up, populations could often rebound and grow again.
It is also important to note, Jensen says, that the study included only one truly cold-water species of fish, the cisco or tullibee. For this species, warming had a clear negative impact – a fact that may soon be true for other species.
As the climate – and our lakes – continue to warm, more and more species will see waters move beyond temperatures they can tolerate. “You can hit temperatures where the math changes,” Jensen says. “Just a couple more degrees of warming, and all bets are off.”
Still, for the moment, he says, this study provides some good news. “Climate change often leaves us with a sense of powerlessness because it’s an inexorable force happening globally and our ability to impact it at the local level is minimal,” Jensen says. “This research left me with a sense of hope. We may not be able to control power plant emissions in China, but we can certainly have an impact on our local fisheries regulations.”