By Dr. Hal Schramm

Have you ever wondered whether bass are getting harder to catch? Fishery biologists, too, have been intrigued by this question. Several studies in small research ponds in the 1970s found largemouth bass became less vulnerable to angler capture after several fishing trips, even though the fish were immediately released. The decline in catchability—the probability of being caught with a fixed amount of effort—was attributed to learned lure avoidance.

To those who think fish feel pain and have the same powers of reasoning as humans, this makes sense. The punishment (“aversive stimuli” or “negative reinforcement” in the parlance of psychologists and scientists who study animal behavior) of getting jabbed in the mouth by a sharp metal object deters bass from future attempts to eat a piece of plastic junk food with one or more shiny hooks dangling from its belly. If you don’t buy the fish-feel-pain argument purveyed by animal welfare enthusiasts -- and multiple lines of scientific evidence support the conclusion that fish do not feel pain -- the “lesson” a bass learns from being caught may be motivated by the restraint on the end of a fishing line.

That fish can learn is well established from numerous studies. One study found that individual largemouth bass avoided an artificial lure after a 5-minute exposure it, and retained this behavior for up to 3 months.

A more-recent study by University of Florida researchers adds further insight to bass’ learning abilities. Dr. Mike Allen and a team of graduate students fished a 26-acre lake for 12 days over a four-week period using only lipless crankbaits and soft stickbaits. The catch rate with the crankbait fell from 2.5 to 0.5 bass per angler-hour after only three days of fishing. Catch rate on the stickbait also declined but much more slowly—from 1.8 bass per angler-hour at the start of the experiment to 1 bass per hour after 12 fishing events.
Not only did the bass appear to learn to avoid capture, they learned to avoid the “stimulus rich” crankbait (rattles, heavy vibration/water displacement, bright baitfish flash, quick movement) faster than the subtle and silent stickbait.

So, it is safe to conclude that learning can reduce catchability, at least for short periods of time. But what if some fish were just innately less aggressive at striking, or more cautious about what they attempted to ingest? In a study that spanned almost two decades, Illinois Natural History Survey fishery scientists tested whether catchability is an inherited trait.

Adult largemouth bass in a 17-acre impoundment were fished for a summer and marked each time they were caught. The lake was drained, and fish that were caught multiple times—the highly catchable fish―were then stocked into a pond to spawn; fish that were caught infrequently or not at all—the low catchable fish―were stocked into another pond to spawn. The progeny were reared to adults, fished, and again the highly catchable and lower catchable fish were spawned in separate ponds.

After three generations of selective breeding, the catch rate of the highly catchable fish remained the same, but the catch rate of low-catchable fish declined with each successive generation. Vulnerability to capture—catchability—was a heritable trait!

The implication is clear:  angling, through harvest or even with the relatively low mortality associated with catch and release, can reduce the catchability of a bass population. By the way, the heritable basis for catchability presents a very strong argument for providing the best care to caught bass, whether you release them immediately or retain them to weigh in a tournament. . So, are bass getting harder to catch? I’ll let you think about it.

In my next blog I’ll share some long-term trends in catch rate from real-world fisheries in large lakes, reservoirs, and rivers throughout the United States to help you better answer the question of whether bass are getting harder to catch.