How anglers are changing the catchability of fish
For many outdoor enthusiasts, fishing borders on an obsession—the thrill of the chase may be just as rewarding as landing a big catch.
There are many ingredients that go into catching a fish: selecting the correct spot and time of day, choosing the perfect bait and deciding where to cast. Even if you've carefully weighed each of these factors, you still need a little bit of luck. If not, you might be going home empty-handed, placated with the old adage, "that's why it's called fishing, not catching!"
But, what if you were actually being outsmarted by fish? And what if it's your own fault?
Researchers are beginning to understand the role that anglers—people who fish with a rod and a line—play in shaping fish behaviour, and the results show that fish are adapting to our tactics, and becoming less "catchable."
The end of the line
In 1977, on a small lake in Fox Ridge State Park in Illinois, researchers began an intensive experiment that would forever change the way we think about fishing.
For three years, they carefully monitored all fishing activity, measuring and marking every largemouth bass that was caught, before releasing it back into the waters of Ridge Lake. Then in 1980, researchers drained the lake. Each fish was collected and sorted, based on its capture history: fish that were caught four or more times were considered highly vulnerable to angling, while those that were never caught were identified as low vulnerability.
The researchers then used these two groups as breeders, and embarked upon a study on fish behaviour that continues to influence fisheries management today. These high- or low-vulnerability lineages were reared separately in experimental ponds for another three generations.
More than 25 years later they showed definitively that vulnerability to angling is a heritable trait that is passed from parent to offspring. In other words, if you are a largemouth bass and your parents got hooked by an angler, you might well face a similar fate. This also means that when these angling-vulnerable fish are removed from the lake, the remaining population will be less catchable.
It was the first demonstration that recreational fishing, or fishing for fun, could cause evolutionary changes in how fish behave.
A matter of taste
Exactly how angling causes fishes to adapt depends on what fishy features a particular angling style attracts. To be caught a fish needs to encounter a lure, decide whether or not to bite and even choose how aggressively to attack the lure.
Researchers have shown that using bright, flashy baits can provoke bolder, more aggressive individuals to strike a lure. On the other hand, using a subtler approach like the classic worm-and-bobber may entice more timid fish in for a nibble. So, the way we fish influences the personalities of the fish we catch.
Because fish personality is related to feeding patterns, it also affects features like body size and activity. A study in Connecticut showed that largemouth bass from lakes with high fishing pressure had lower energetic demands than bass from lakes where fishing was banned. By favouring fish with lower appetites, angling could have far reaching implications for fish populations.
Even the brain chemistry of fish is related to their catchability. Recent research found rainbow trout with brain hormone profiles for lower stress responses were more vulnerable to angling. This means that stress-resilient fish are more likely to be caught, and that anglers could inadvertently be leaving behind low-activity fish that are easily stressed-out.
Put the big ones back
To protect wild fish from overexploitation, many jurisdictions have rules in place to restrict the timing, location, size and number of fish harvested. However, the presumed benefit of so-called non-consumptive practices, like catch-and-release angling, is not necessarily as simple as leaving more fish in the wild. Even when fish are returned to the water, being caught can alter fish behaviour in the short-term (during their recovery) and the long-term (by learning to avoid capture).
Like most wild animals, fish actively avoid contact with humans (and other predators), so being caught is naturally a stressful and exhausting process. After fish are released, stress hormones can remain elevated for hours or even days depending on the species.
Just as in humans, being stressed out can impact a fish's ability to carry out routine tasks, such as feeding or hiding from predators. So, it makes sense that fish released by anglers might try to avoid another encounter in the future.
Switch it up
In fact, many fish can learn from previous capture experiences. Researchers in Norway studied how often caught-and-released Atlantic salmon were recaptured on the same or different baits and found that fish preferentially avoided the same lures.
By creating a population of fish that is more timid, anglers also reduce their own success. For example, in a study of British Coumbia's small lakes, researchers found that a sustained fishing effort from large group of anglers reduced the number of rainbow trout they caught after only one week.
Scientists are learning that how we fish has a big effect on how fish respond. If fishers continue hitting the same spots and pulling out the boldest, most aggressive fish year after year, they are likely to soon find it harder and harder catch anything at all.
If this situation sounds familiar, it's exactly why many anglers opt for catch-and-release only. But, it goes beyond putting the big ones back.
To maximize your catch—and the catchability of wild fish—consider fishing for different species, trying different spots and changing up your lures. This can make for less stressed fish —and even happier anglers.