Catchability Counts
One of my memorable revelations occurred as I sampled largemouth bass at several Georgia reservoirs. As a biologist with the Georgia Department of Natural Resources (DNR), I learned the art of electrofishing as we collected bass for routine sampling and tagging studies. I recall pushing down the pedal (to activate our electrodes, sending voltage into the water) by a dock in a small creek of Lake Walter F. George (also known as Lake Eufaula). Out rolled six or seven massive bass, an immediate 25- to 30-pound tournament limit. I’d fished those waters and caught decent fish, but nothing like what we discovered.
That scenario was repeated around shoreline brush and many other obvious bass fishing targets on this and other waters we sampled. Our collecting found spots that were stacked with big fish, but guys fishing nearby weren’t having much success. And when I returned to the lake with my boat in tow, I was unable to muster comparable results.
I wasn’t alone. In the late 1980s, the Alabama Department of Conservation and Natural Resources and Georgia DNR were petitioned by bass fishing groups and chambers of commerce to stock largemouths in Lake George. Catch rates were low. Anglers were going elsewhere and calling it “fished out.”
From our sampling, we knew that was far from the case, but did our best to refrain from belittling the fishing skills of locals. Finally, Alabama fishery workers brought members of the public along in the electrofishing boat. After few hours of sampling, demands for management action ceased. Why was catchability so low? Theories abounded; we still don’t know.
More recently, I’ve lowered my Aqua-Vu camera to reveal dozens of big smallmouth bass scattered out among rocks and sand in 22 to 23 feet of water. I excitedly pitched a drop-shot rig and waited for a bite that finally came. But it was a 13-inch largemouth. “Where did he come from I wondered,” as I dropped back and came up with a half-pound smallmouth. I lowered the camera to verify their presence, but I couldn’t buy a bite in almost two hours.
Pressure Effects
We also know that bass learn about lures through being caught or seeing others caught, and they become harder to catch. We’ve reported on the tests at Berkley’s Fish Lab where naive bass (never fished for) quickly learned to ignore hookless crankbaits towed around a huge pool. Recognition of the fakes remained when they were tested again after several weeks passed, as few strikes occurred. Presumably, biting something that gave no reward was enough to teach them to avoid lures.
Frequent In-Fisherman contributor Dr. Hal Schramm reports that a 2018 study at Mississippi State University, where he served as Leader of the Cooperative Fish and Wildlife Research Unit, shed further light on how fishing affects catchability. He and a team studied ponds stocked with bass and fished them, recording one angler hour per acre per week. The study covered two years and involved the catch of 1,156 bass. Some ponds were fished for 24 weeks in a row, while others were fished for two months, then left alone for two months, after which fishing resumed for an additional two months. Anglers systematically fished at different times of day from May to October and used 11 different types of lures.
Predictably, fishing success declined rapidly, though all bass were released, dropping from about seven bass an hour to just one. In ponds that went unfished for two months between regular fishing, catch rates returned to about 60 percent of the initial level, then quickly declined to a bass per hour. So most bass seemed to initially forget what they’d learned—to avoid lures, but catch rates quickly fell, suggesting that they wised up fast. The semi-wild conditions of the ponds contrasts with the stark surroundings of Berkley’s tank, suggesting that bass in truly natural conditions may also forget about fishing pressure when anglers are scarce.
Genetic Effects
Experiments on small lakes have revealed that individual largemouth bass vary considerably in their catchability, as determined by their likelihood of capture with artificial lures. The most detailed investigation was conducted by a team of researchers at the Illinois Natural History Survey, headed by Dr. Dave Philipp, published in the Transactions of the American Fisheries Society in 2009. It was the culmination of studies that started in the late 1970s.
They fished these waters and also electrofished, marking all bass. Fish that were caught four or more times by angling—highly vulnerable bass—were then stocked into empty ponds and allowed to spawn. Bass that were never caught or only once—low vulnerability fish—were placed in other ponds. After four years, mature fish were collected from each pond, tagged, and fished. These bass represented the offspring of highly catchable and low-catchability parents. They differed even more than their parents, as catch rates increased further in the high-vulnerability group and dropped for the less vulnerable one. This cycle was repeated a third time in the next generation, and results were similar. Offspring of tough-to-catch fish became even tougher to catch. The increase in catchability was less in the third generation, but still amounted to about a fish per three hours of fishing.
The authors noted that these results indicate that fisheries with high harvest levels have been selecting for more wary bass via the removal of more vulnerable fish. This undoubtedly was an important factor years ago in popular lakes and reservoirs before the catch-and-release ethic caught on in the 1980s. Today, with release rates well over 90 percent in most waters, and tournament survival at a similar level, genetic effects may be moot. But it provides answers when we wonder why many popular fisheries that contain lots of bass can present fishing so challenging that numbers of top pros can barely scratch out a few small keepers over several days.
The more we learn about the behavior of bass, the more we recognize the many differences among individuals. It’s generally true that in a particular lake a bass is a bass, but one bass may not behave at all like another.