One of the strange joys of fly fishing is you are often forced to think while you fish. Am I fishing with the correct fly? Is it in the right place or at the right depth? Are the fish even feeding? Even when we expend considerable mental effort, there are days when we have little or no idea why our flies fail to deliver. Many folks chalk this up to bad luck and get on with their lives. However, there are some of us who are simply unable to ascribe these failures to chance.
The mysteries of why fish do or don’t take f lies has fueled countless streamside conversations and filled the pages of many books. As with so many things in the natural world, the underlying driver of fish behavior is evolution, which has been shaping their biology for about 530 million years. That’s a very long time and hard for most of us to visualize. It might help to think of this as a story with every page representing a year. The distance between covers of this book would be almost three times the height of Mount Everest. Thankfully, biologists have been busy, and we now have a better idea of what is going on when fish ignore our flies. The picture is far from complete, but it’s starting to look like we may have to think harder about how we fish.
Learned Behavior
Most of us have probably experienced refusals, when a fish decides, for some reason, not to take your fly. I’ve lost count of how many times this has happened to me. You can get refusals from all kinds of fish in all kinds of waters. In clear water such as the Fall River, you get to see this in glorious high definition. Your carefully tied and perfectly presented fly drifts into the strike zone. The trout spots it, moves to intercept, and then decides it’s got better things to do. Largemouth bass can do this with top-water patterns, and it can drive you absolutely nuts. It’s hard to remain calm and collected when the business end of a large bass hovers right below your fly for longer than you can hold your breath, only to melt away like Lewis Carroll’s Cheshire Cat. And these are probably just the tip of the iceberg. Imagine how many times refusals happen when your fly is too deep to see.
Most of the time, we assume our presentation or pattern wasn’t quite right. But what if the fish remembered trying to eat something like your fly before? Have you noticed how often a hot pattern emerges onto the scene, only to be forgotten a year or two later? Studies have shown fish remember interactions with fishing gear. How many times a fish needs to be hooked with the hot fly before it learns to avoid it probably varies among individuals and species. But learn they do. In addition, there’s evidence in rainbow trout that fish learn from watching the behavior of other fish. “Monkey see, monkey don’t do” applies to fish, as well. And this lesson can last a long time. Carp have been shown to remember specific colors for at least a year. This may well explain why a hot fly doesn’t stay hot for very long.
Of course, this learned behavior probably isn’t limited to the fly. Tippet flare, where the tippet deforms the surface film, creates a bright crease that really stands out on flat water. For dries and shallow nymphs, this may be enough to alert the fish long before your fly reaches the strike zone. Visual effects aren’t limited to the tippet, either. Sloppy casts will often hit the water hard, creating a lightninglike bubble trail that streaks directly toward the fly. I’ve got underwater videos that clearly show this effect on both calm and rippled waters. You can reduce this effect by using fly lines with long front tapers, but improving your casting is the best antidote.
Smell
You may recall a 2018 “Gearhead” column where we discussed the effect of smell on fishing success. To recap, fish have evolved an incredibly good sense of smell and are able to detect many natural and synthetic compounds in concentrations as low as parts per million or even parts per billion. This allows them to detect things such as food and predators and, in the case of migratory fish, their breeding grounds.
Hunters often go to great lengths to reduce their scent, with special underwear, carbon filters, and even ozone generators. There are good reasons to believe fly fishers should be doing likewise. An incredibly small amount of the wrong stuff on your fly could trigger a negative response from the fish. One example of the wrong stuff is L serine, a chemical found on the skin of bears, a natural predator of trout and salmon. Both fish species react to very dilute concentrations of L serine. In the case of coho salmon, as little as 10 parts per billion will elicit a response. L serine is found on human skin, too. As far as the fish are concerned, you smell like a bear. If you just tied on a fly, you may have transferred L serine from your skin or saliva to the fly.
As any decent guide will tell you, the first cast to a big fish is the most important one. Your chances of connecting go down with each subsequent attempt. This is why you’ll want to make sure your fly isn’t sporting any offensive chemistry. It makes no sense to tie on the perfect fly, make a perfect cast, and then watch the fish come close to the fly, only to swim away because it smells wrong.
If you are super serious about targeting the biggest or most challenging fish, you may want to consider “deodorizing” your fly before you pitch it to a fish. Fortunately, this is really easy to do. It takes only a few seconds to dip a fly in a small bottle of diluted (unscented) detergent, followed by a thorough rinse in the stream or lake. I realize some folks will roll their eyes at this suggestion. Often enough, such skepticism is well founded. Most of the time, our flies have had enough time in the water to be deodorized. But that may not be the case with a fly you’ve just tied on.
Timidity Syndrome
A paper published in 2017 in the journal Fish and Fisheries detailed some fascinating experiments on largemouth bass. The study showed that bass have significant differences in vulnerability to angling, with some being more vulnerable and others less so. Anyone who has fished for bass has likely noticed how some of them are easy to catch. They’ll attack poppers and streamers with wild abandon. These are the bold members of the population. In addition to these bold fish, you’ll probably notice some timid bass that aren’t so excited about your flies. Some of them may even flee when your fly hits the water.
The researchers were able to show that the offspring of bold fish were also highly vulnerable to angling. But the astounding finding was that under catch-and-release fishing, subsequent generations of timid fish were less vulnerable than their parents. By the third generation, the timid offspring had become 2.25 times less vulnerable than bold fish. It seems highly unlikely this is a learned behavior, so it’s quite possible catch-and-release angling causes epigenetic changes in the offspring of timid fish. The researchers called this effect “the timidity syndrome.”
The timidity syndrome has been demonstrated in other species of fish and is possibly found in all fish. From an evolutionary perspective, this makes sense. Under low predation and low food conditions, the bolder fish will have a reproductive advantage, since they will consume more food. Conversely, high predation would tend to select for more timid fish, since the bolder individuals are more likely to be taken by predators.
This may explain why fishing some waters can be much tougher than others. Angling basically exerts the same pressures as predation, so the removal of bold fish will skew a population toward timid fish. This is likely more pronounced in fisheries where most fish are killed for the table, but catch-and-release angling will also have an effect. With a typical mortality rate of 5 to 10 percent, even catch-and-release fishing will increase the proportion of timid fish over time.
This is another good reason for all of us to practice sound catch-and-release techniques. Inadvertently making fishing harder by removing 5 to 10 percent of the bold fish from the population (and hence the gene pool) is a good way to reduce the number of fish you catch and increase the probability of getting skunked. If you are a guide who fishes unstocked waters, this could even affect your bottom line. Less skilled clients are going to have fewer hookups, which could translate to smaller tips and less repeat business. You don’t need an MBA to realize this isn’t a good longterm business strategy.
Technology
It will come as no surprise that we are fishing with gear that is better than our parents or grandparents used. Whether it’s new fly lines or new fish finders, each advancement puts additional pressure on the fish. On waters where fish are regularly stocked and there is no natural reproduction, this will tend to increase the capture of both bold and timid fish. But bold fish will be more affected, and as a result, the fishing will tend to become tougher as the season progresses. Fortunately, next year’s restocking should restore the balance.
The story is quite different for unstocked waters. In this situation, the bold fish will be less likely to reach maturity and breed than their timid friends. As a result, the proportion of bold fish will be lower in subsequent years until a new (stable) boldness/timidity ratio is reached. Heavy fishing pressure will also have the same effect on timid individuals, most likely biased toward the mildly timid. This will push the overall population toward even more timidity. Even if the total number of fish in the water remains the same, anglers may assume there are far fewer fish than there used to be.
Combine the effects of learned behavior, timidity syndrome, and new technology on wild fish and you get a situation where the fishing can become really challenging. European carp anglers have been facing this situation for decades. Carp nuts will spend years and thousands of dollars attempting to catch a specific (often named) fish that is so cautious it may have been caught only a couple of times in its life. I’ve seen something similar at a bass lake. Over the past decade, the fishing has become tougher, with only the most knowledgeable locals doing well, and even they have very tough days. I have electrofished the lake and know it still holds plenty of bass.
There are other potential long-term implications for our technological advances. Largemouth bass anglers are a highly creative and often competitive bunch who readily adopt new technology and techniques. Their ability to locate fish and present lures that can mimic a wide variety of prey may put increased pressure on bolder, fast-growing fish. Over several years, this may reduce the breeding success of these fish, skewing the fishery toward slower-growing and more timid fish. The latest side-scan fish finders can locate individual fish very close to cover and show, in real time, exactly how they respond to a lure. This has the potential to accelerate the shift toward smaller, more timid fish. Simply put, as our tools and techniques get better, the fish may well respond by becoming smaller and harder to catch.
There’s no reason to assume this can’t happen on your favorite trout water. Take Euro nymphing, for example. This highly effective technique has been embraced and advanced by competition fly fishers in Europe and the United States. Guides and ardent fly fishers continue to refine the technique and gear further to match the waters they fish. As more and more people fish the same stretches of water with the same flies and techniques, it’s almost inevitable the fish population will respond. Catch-and-release practices and the ability of fish to learn from observing other fish will likely decrease catch rates for many regular fly fishers. If trout have the same epigenetic response as bass, the population will inevitably skew toward more timid fish.
So what’s a passionate fly fisher to do? Perhaps the most logical thing is to stop doing what everyone else does. If the fish have been hammered with fast-sinking nymphs, try using wet flies or streamers. Instead of fishing the same water as everyone else, cast your fly into places that most folks ignore. Learn how to dead drift a dry over glassy glides or to fish nymphs upstream.
If you aren’t fishing for the table, do everything you can to ensure every fish you hook will survive. Trout Unlimited and other organizations provide all kinds of good information on how to practice catch and release really well. This is where I see guides playing an incredibly important educational role. If you practice catch and release effectively, your clients are likely to do the same.
When fish ignore your f ly, it’s not just bad luck. There are reasons, and they’re all connected to the kind of beings the fish are and the things we do when trying to catch them. Those reasons should give you some interesting topics to discuss during your next slow-day streamside chat.