January 17, 2024
Research Findings: Tournament Mortality of Largemouth Bass
Competitive angling continues to grow in both freshwater and marine fisheries, with more than 50,000 fishing tournaments held annually in the United States. These events, potentially involving hundreds to thousands of anglers and lasting hours to days, may result in tournament-associated mortality of captured fish. Most tournaments, however, are catch-and-release to conserve fish populations and angling quality. Fish caught at tournaments that die prior to release are easily observed, but mortality of fish released following tournaments can be substantial yet cryptic and difficult to quantify. Knowledge of post-release mortality is vital to understanding the effects of tournaments on populations.
To estimate post-release mortality at tournaments, we tagged and recaptured largemouth bass at tournaments and through boat electrofishing in a central Iowa reservoir with more than 40 bass tournaments annually (more than 13 tournament angler-hours per acre per year). Recapturing bass that were tagged at tournaments allowed us to estimate daily survival rates following tournaments, compared to bass that were captured by electrofishing and tagged. We also assessed how water temperature and the number of times a bass had been previously caught may affect bass survival.
A total of 3,423 bass greater than 15 inches were caught at 131 bass tournaments, and an additional 2,168 bass were captured during 129 hours of electrofishing from 2015 to 2018. Of the tagged bass that were recaptured, 1,196 were caught at tournaments and 745 were captured during electrofishing. Over 3.5 years, at the fishing tournaments, 82 percent of bass were caught once, 15 percent were caught twice, 2 percent were caught three times, 0.09 percent were caught four times, and 0.01 percent were caught five times.
We observed 86 bass that died before or during weigh-in (initial tournament mortality). Post tournament release, we found that bass caught at tournaments had lower survival for three days following tournaments, compared to those not captured during tournaments. Bass survival also decreased at higher water temperatures and was lower for those previously caught at prior tournaments. For example, in a theoretical tournament where 100 bass are caught, we estimated 15 of them would die at a water temperature of 54°F, whereas at 66°F, upward of 34 would be expected to die. Further, bass caught at five tournament events could result in up to 90 percent cumulative mortality at higher temperatures. We did not find evidence suggesting fish size was related to tournament mortality.
Our results confirm the potential for delayed mortality associated with catch-and-release fishing tournaments and the importance of water temperature and prior tournament angling pressure on bass survival. Tournament organizers may consider catch-photo-release tournaments during warm-water periods to reduce bass mortality.
–Dr. Andrea Sylvia and Dr. Michael Weber, Iowa State University
Sylvia, A., and M. J. Weber. 2019. Use of a mark-recapture model to evaluate largemouth bass delayed tournament mortality. Fish. Res: 219,105335.
Field Science: Factors Affecting Pike Catch Rates
Researchers studied the effects of environmental variables on angling catch rates (fish caught per hour) of northern pike in a lake in Germany. Factors tested included water temperature, wind speed, wind direction, humidity, rain, hours of sunshine, atmospheric pressure, pressure change during the last 24 hours, lunar cycle, fishing pressure, and time of day.
Twenty-five anglers fished from May to September 2005, using their choice of artificial lures and natural baits. All pike were released after unhooking. Immediate hooking mortality was 3.9 percent.
Catch rate fluctuated widely during the study, but was significantly related several variables. Catch rate increased at dusk, with high wind speed, and around full and new moons. It declined with rising water temperature and when fishing pressure was high two days prior to test fishing.
Pike were more vulnerable to angling during twilight periods. This may be due to increased feeding in lower light, or because pike aren’t as readily able to differentiate food items from artificial lures in low-light conditions, the researchers suggest. Similarly, high wind speed might reduce light penetration at the surface and enhance turbidity, creating dimmer conditions that limit pike vision.
The researchers note that fishing pressure the prior two days was a much more important predictor of catch rate than other environmental variables, and that pike can alter behavior in response to being caught, or to other disturbances caused by fishing and boating. Results indicate that the potential memory of pike to avoid future capture appeared to extend to two days, because catch rates weren’t affected by fishing effort 3 and 4 days prior.
*Kuparinen, A., T. Klefoth, and R. Arlinghaus. 2010. Abiotic and fishing-related correlates of angling catch rates in pike (Esox lucius). Fish. Res. 105:111-117
Natural Wonders: World’s Oldest Aquarium Fish
What’s apparently the oldest fish in captivity is at least 90 years old, living at the Steinhart Aquarium, part of the California Academy of Sciences in San Francisco. This Australian lungfish, known as Methuselah after the 969-year old grandfather of Noah in the Old Testament, arrived in 1938 and lives with several other younger specimens. Another Australian lungfish named Grandad lived at the Shedd Aquarium in Chicago for many years, but passed away in 2017 at age-95.
She weighs 25 pounds and is 4 feet long and aquarists believe Methuselah is female, but it’s not entirely clear. “She loves getting her back and belly rubbed and has a mellow personality,” says Jeannette Peach of the California Academy of Sciences. “She can be a picky eater. She likes figs, but only fresh ones, not frozen.”
Lungfish (six species are found in Australia, South America, and Africa) are primitive species with both gills and lungs, allowing them to live in dry mud balls for extended periods of drought. They’re thought to be an evolutionary link between aquatic and terrestrial animals. Australian lungfish have existed for at least 100 million years, but are now on the Threatened Species list.