Fish sizes and tendencies impacted by climate change: ELA

By Daniel Adam
Staff Writer

A group of experimental lakes in Northwestern Ontario is helping researchers learn more about aquatic trends. The Experimental Lakes Area (ELA), located about midway between Kenora and Dryden, has conducted many studies over the years, with various topics including acid rain, estrogen, microplastics, wastewater, and mercury.

Research fellow Mike Rennie is a Canada Research Chair in Fisheries and Ecology. He is also an associate professor at Lakehead University, where he says over half of the work his students do is ELA-related research. Some of the studies he’s been doing lately have been related to climate change and how it affects certain species.

“There’s been a fair amount of work in the marine environment to suggest that warmer conditions lead to smaller fish overall,” he says. “So if you’ve got fish species like bass and pike who like warmer water … it suggests the ‘big fish’ that we might have caught 30 years ago, we may not see anymore because of climate change.”

He says over the last 60 years in Northwestern Ontario, the average air temperature has increased about 2 degrees C, and the ice-free season has extended three weeks. Rennie says they’ve noticed that over the last 30 years, lake trout are spawning about a week later on average.

“It doesn’t sound like that big of a deal,” he says. “Well, lake trout spawn in the fall, and then they have the winter under ice to develop. If the period of ice cover is shrinking due to climate change, then we’re also reducing the incubation time period for lake trout. So there’s some concern that once you hit a particular point in that incubation period, maybe you enter a situation where you’re unable to support lake trout anymore.”

But lake trout aren’t the only fish impacted by temperature change. Rennie says white sucker growth rates are much slower than they used to be.

“If you looked at a five or six-year-old sucker 30 years ago, it would be about 40 cm,” he says. “And now, they’re about half that size.”

Rennie says since white suckers are all over North America, they make a good sentinel species. Sentinel species are an organism that can help provide advance warning of danger to humans by detecting risks in the environment. One example is canaries in coal mines. If the bird died, that would alert miners to a high concentration of odourless carbon monoxide, giving them time to safely escape.

In ELA’s secluded region, it’s easy for them to know that their results aren’t being altered by outside factors like commercial fishing, invasive species, or cottage septic systems. Since those things aren’t happening in their system, researchers can isolate particular effects and their impacts.

Rennie says ELA is permitted to manipulate 58 lakes, but only use about two or three at any given time. He says doing a whole ecosystem experiment would take a lot of resources, and their team is small.

He says the lakes they use are easily accessible and are sometimes “recycled” from one experiment to the next. Rennie says the experimental lakes are relatively small. His work focuses on fish, so mark-and-capture studies — to estimate population sizes — are much simpler in a smaller area.

The lakes are anywhere between 20-50 hectares. Some are quite shallow, at only a few metres deep, while some of their trout lakes can be between 13-30 m.

“Teggau Lake is right next to us. That goes down to like 150 or 200 meters. We don’t usually actively work on that for research,” he says. “But we’ve got a lot of diversity in the area around where we do our work.”

He says a typical fish community at ELA would have lake trout (if deep enough), pike, white sucker, perch, and a handful of minnow species.

Rennie says for all experiments they’ve done, the fish populations have recovered several years after the manipulations have completed. Rennie gave a relatively recent example of an aquaculture study.

“We ran a cage culture operation for five years in a small lake, then saw big changes in terms of the growth rates of native lake trout and population sizes of those fish,” he says. “And within two years of ending the cage culture operations, the population sizes were back to what they were before the experiment. Growth rates took about a similar amount of time to recover, while certain other attributes took longer to recover, maybe on a scale of like five to seven years.”

He says results vary depending on the nature of the research.

“Acidification is going to have a different impact than, say, nutrient additions, or adding mercury,” he says. “So it really depends on what you’re trying to investigate, and what the goals of the experiment are.”

He says ELA also did a study that observed the impacts of atmospheric mercury deposition, more specifically, mercury concentrations in fish. To specifically study ELA’s added mercury, there needed to be a way to differentiate it from any already-existing mercury.

“You can get mercury of a specific isotope, and if you analyze it correctly, you can understand which mercury is the stuff that you added versus what was already there,” says Rennie.

He says ELA added very small amounts of “labelled” mercury directly to the lake and to the surrounding watershed. The idea was that the mercury added directly to the lake represents inputs from precipitation, while the mercury that was added into the watershed — with a different label — would be older mercury that has hit the land and slowly moved down into the lake.

“So they added mercury for several years, and what they found was that all of the mercury that they saw showing up in fish and other organisms was the stuff that was added directly to the lake and it started showing up right away,” says Rennie.

He says when ELA stopped adding mercury, within a couple of years, in very short-lived species like yellow perch and shiners, the mercury came back down to background levels. But it took bigger fish like whitefish or pike a longer period of time — up to a decade.

“The important thing here is that it showed that if we can reduce atmospheric deposition and mercury, then we should expect to see reasonably immediate reductions in fish mercury concentrations as atmospheric levels decrease,” says Rennie. “The experiments we do can actually help guide environmental policy to make better decisions as to how to improve things in our environment. In Northwestern Ontario, everyone loves fishing, so if we can make the fish that we’re catching safer to consume … that should be a good thing.”

Rennie says research forming international environmental policies is not a new concept. He referenced acid rain experiments which shaped the Clean Air Act in the ’80s.

When ELA was originally conceived in 1969, it was set up to understand issues around nutrients; in particular, what was responsible for harmful algal blooms.

In those days, Lake Erie was being called a “dead lake,” and no one could agree on what nutrients should be limited. Rennie says it was UCLA research that helped demonstrate that it was phosphorous. As a result, many detergent companies began making phosphate-free products.