URBANA, Ill. (U.S.A.) -- If you’ve ever been on a fishing boat, you might be familiar with live wells – small water tanks, built into the boat, where live fish can be stored. In bass fishing tournaments, these live wells keep fish alive throughout the competition, so that they can be released at the end. Anglers are always looking for ways to keep fish safe and healthy in these wells, since live bass mean higher prizes and more fish spawned for next year.

Researchers at U. of I. studied the effect of live well temperature variation on largemouth bass health and recovery time during tournaments, and shared their results in the North American Journal of Fisheries Management.

Cory Suski, professor of natural resources and environmental sciences, part of the College of Agricultural, Consumer and Environmental Sciences, and his former master’s student, Allison Hay, found that live well temperatures are highly variable, in part due to angler’s activities during tournaments. Temperature variations can negatively impact bass’ activity upon release, they discovered.

The largemouth bass angling landscape

Previous studies have found that tournaments can be deadly for captured fish, with mortality rates approaching up to 43% in some events, particularly in warm summer months. Because around 32,000 angling events take place across North America annually, minimizing mortality is crucial to ensure fisheries stay healthy and usable for decades to come.

“Angling itself is pretty benign,” Suski said. “But live wells are the longest point of contact between the angler and the fish. So the anglers have a lot of potential to influence the fish during that period.”

Unfavorable live well conditions, such as low oxygen and crowding, pose physiological challenges to individual fish and stress a population that is caught and released repeatedly across multiple tournaments. Because largemouth bass are the most popular target for tournament anglers, improving outcomes for them could have major conservation implications.

The study was developed in coordination with the Illinois Department of Natural Resources. Because state entities are responsible for enforcing fishing regulations, their relationship with anglers can become strained, Hay said. “I came in as the third party, and I noticed there was a lot of variation in practices across these anglers, just by having conversations with them.”

Forging connections with anglers

Anglers are motivated to keep their fish in good health, both out of love for the animal and the sport, and because points are deducted when fish die. Some anglers use ice to cool down their live wells, thinking that this will benefit the fish. Newer bass boats have recirculators, which pump in water from outside the boat. This means temperatures in a live well might oscillate throughout a tournament, causing fish physiological stress. “It’s like being in the shower and someone flushes the toilet,” Suski said. Stressed fish have longer recovery times, and need more time to resume normal activities once released.

But research on these methods is lacking, the scientists said. “The angling community puts a lot of stock in word of mouth – what they hear from people in their community, maybe on social media, maybe just their friends at the bar,” Hay said. “So if we have these false narratives of what’s good for a fish, that can be really detrimental and exacerbate a problem they didn’t know was happening.”

By interacting directly with anglers during tournaments, Hay and Suski could find out what was actually happening, and figure out whether methods could be improved.

To this end, the researchers’ first step was to collect live well temperature data during four 2023 tournaments at Clinton Lake, in Dewitt County, Illinois. This meant showing up to tournaments, building relationships, and gaining the anglers’ trust.

“I grew up in the middle of nowhere, East Texas, so there's a little bit of an overlap in the culture, and I felt like I could relate to the anglers a little bit more,” Hay said.

“Ninety-nine percent of the study was Allison's relationship building,” Suski said. “One percent of it was the technology just changed.” While anglers might be hesitant to allow scientists to put cumbersome equipment on their boats, they didn’t mind the team’s new, unobtrusive temperature sensors, the size of a few stacked quarters.

Understanding live well conditions

In the lab, Hay and Suski conducted simulations of the conditions they noted at tournaments, exposing largemouth bass to temperature variations and other stressors, such as exercise. To quantify the impact of temperature changes on the fish, the researchers assessed their reflexes and analyzed the animals’ blood for indicators of physiological damage.

The team found that live well temperatures changed drastically throughout tournaments, particularly if anglers added ice during the fishing day, and that this had a negative impact on largemouth bass. While no fish in the study died and their reflexes were not impaired, temperature oscillations exceeding 5 degrees Celsius (around 7 degrees Fahrenheit), generated physiological stress as indicated by blood analysis.

Making evidence-based practices accessible

Hay and Suski recommend that anglers refrain from adding ice to their live wells, and instead encourage them to aim for consistent temperatures, as close to surface water temperatures as possible.

Suski continues to research bass health during angling tournaments, and the researchers hope to make evidence-based angling recommendations more widely accessible. They continue to work on sharing their results widely amongst anglers and fisheries managers, such as the Department of Natural Resources.

Hay hopes that this study will encourage communication between anglers, managers, and scientists. “They love fish, and I love fish,” Hay said. “So I really wanted to emphasize that I'm not there to take this resource away from them. I'm there to make sure this resource is here for them and their kids and their grandkids.”

The study, “Quantifying the impact of temperature variation in live wells on Largemouth Bass,” is published in the North American Journal of Fisheries Management [DOI:10.1093/najfmt/vqaf016]. Authors include Allison Hay, Jackson Glomb, Reagan Oller, and Cory Suski.

The research was supported by the Federal Aid in Sport Fish Restoration Program via the U.S. Fish and Wildlife Service administered by the Illinois Department of Natural Resources, project 391-F-202-R-4, along with US Department of Agriculture National Institute of Food and Agriculture Hatch Project ILLU-875-940- awarded to Cory Suski, an Illinois Muskie Tournament Trail Research Grant awarded to Allison Hay, an Illinois American Fisheries Society Student Research Award awarded to Allison Hay, and Natural Resources and Environmental Sciences HATCH Summer Internship Program awarded to Reagan Oller.

Cory Suski is also affiliated with the Institute for Sustainability, Energy, and Environment, the Prairie Research Institute, and the Center for Latin American and Caribbean Studies.