Studies of largemouth bass, as well as several other fish species, including brown trout, rainbow trout, common carp and northern pike, have found that angler catch rates declines with accumulating fishing effort.
The decline in catch rates has been attributed to fish learning to avoid lures, but whether fish learn to avoid capture has not been clearly demonstrated. Research by graduate student Matt Wegener at Mississippi State demonstrates that largemouth bass do learn to avoid capture by anglers — and they learn quickly.
Six ponds in northeast Mississippi, from 1 to 5.6 acres in size, were fished weekly by two anglers from May to October for two years. All ponds had established largemouth bass, bluegill and redear sunfish populations. Fishing was minimal in these ponds before the study, and all ponds were closed to fishing during the study.
Two researchers fished each pond for one angler hour per acre each week, the same fishing effort as at Mississippi Department of Wildlife, Fisheries and Parks state-fishing lakes. On each outing, the researchers rotated through 11 different types of artificial lures selected to be effective in different habitats found in ponds. The researchers were skilled bass anglers and fished from a two-person “bass buggy” powered by an electric trolling motor.
All fish were handled quickly and carefully, measured and immediately released. No fish were “gut hooked” or bleeding, and survival after release was assumed to be 100 percent. All bass at least 8 inches long were counted in the catch.
In the first year, three ponds were fished weekly from May through October, and three ponds were fished weekly during May and June and September and October but not fished during a July and August closure period. May was selected as the start of the season to avoid bass spawning and fry-guarding influencing catch rate.
During the second year, the three ponds fished continuously during the first year were not fished in July and August, and the three ponds closed to fishing during July and August the first year were fished continuously. In other words, all six ponds got the same fishing treatment.
Wegener found catch rates declined throughout the May-to-October fishing season. In ponds fished without closure, catch rate declined from 6 bass per angler hour at the start of the 24-week fishing season to 1.5 bass per angler hour at the end of the season.
In ponds with closure, catch rates declined from 7.4 bass per angler hour the first week to three per angler hour at the end of June. When fishing resumed in August, catch rate was five bass per angler hour and decreased to 0.8 bass per angler hour at the end of October.
Wegener also measured “catchability” — the proportion of the population caught each week. Like catch rate, catchability declined with continuing fishing throughout the 24-week season. In the ponds with closure, catchability quickly declined during the first 8-week fishing period. Catchability was high when fishing resumed after the closure and quickly declined during the September-October fishing period.
What it means
Largemouth bass catch rates are highest at the start of the season and decline with continued fishing effort. A two-month closure resets the catch rates to a level similar to the start of the season, but the catch rate quickly declines again. Anglers should expect the highest catch rates when a new fishery opens or after a period of low fishing effort, but they should also expect catch rate to be lower late in the season.
The decline in catch was a result of declining catchability of largemouth bass. But was the declining catchability a result of learning as has been suggested by other studies?
Yes, according to Wegener. The decline in catchability supports learning. Forgetting is also evidence for learning. The increase in catch rate and catchability mid-season after closure, and the high catch rates and catchability at the start of the season support forgetting.
Learning can occur by “classical conditioning.” Just like Pavlov’s dog was trained to associate a bell ringing with food, bass could associate the adverse effect of being injured by hooks or restrained by angling after biting a lure. But on each outing, anglers used 11 different lure types to catch fish. Although fish can learn, it is doubtful they lack the ability to generalize among lures.
Wegner suggests that “angler avoidance” might be a more appropriate term than “lure avoidance.” The captured bass may associate the adverse effect of capture with the sound of the trolling motor or the presence of anglers.
To what extent these results from ponds, although replicating actual angling, apply to larger reservoirs is not known. But they do indicate that low catch in heavily fished waters is not necessarily an indication of low bass abundance.