A short time ago, while in my doctor’s office for a routine visit, our discussion turned from medicine to trout fishing. That’s what usually happens, because my doctor is an avid fly fisherman and that’s what we talk about instead of the reason for my appointment.
Anyway, during our visit he asked me a very interesting question, which had to do with the evolution of brown trout feeding behavior.
“Do you think that brown trout are not rising to feed as much as they used to, and is that because of all the eagles and other avian predators lurking over Catskill rivers?” he asked.
“That’s a very interesting question,” I replied. His point had merit.
“Ever since DDT was banned in 1972, eagle populations have steadily increased, in some locations dramatically,” he said. “In fact I’ve observed as many as eight eagles soaring above the East Branch of the Delaware River, near our camp. Those birds all have to eat, and fish, especially brown trout, are a primary food source.”
“So yes, I think that you are right to think that brown trout, in particular, which are the most abundant trout species found in the Catskills, and the one that is historically the most wary, are not taking flies from the surface like they once did,” I said. “And being an excellent fly fisherman and a student of the sport, you are more aware than most that brown trout are particularly sensitive to sunlight and extremely wary of threats from above, like eagles and ospreys. Couple that with guide boats frequently floating on some rivers and fly lines constantly in the air where these trout feed, is it any wonder that browns in particular have learned that feeding subsurface is a lot safer than taking flies off the surface?”
“There is one more factor to take into consideration… and that is that mayfly hatches have declined both in numbers and species,” I continued. “Not so many years ago, Hendricksons, sulphurs and other mayflies covered the water during emergence. We don’t see these huge hatches anymore. Some blame that on climate change, which I cannot confirm or deny. What I can say is that mayflies have been around for millions of years, having survived the last ice age, which ended in this region about 12,000 years ago. In addition, they have adapted to low summer flows and high water temperatures. So the order Ephemeroptera is a very resilient group of insects.”

I went on, “I also know, based on several years of observation, that the increase in cold water releases from Pepacton Reservoir has had a significant negative impact on the number of mayfly species found in the upper East Branch of the Delaware River, and that the hatches of the remaining species have dramatically declined in numbers. So that may also be a reason why brown trout are not feeding at the surface as they once did. There just aren’t enough flies.”
So the question remains: do trout, particularly brown trout, learn to adjust their feeding behavior in response to perceived threats from the air, boat traffic and constant harassment by anglers?
The next question then: of all the species of trout in the world, why are brown trout the most wary and difficult to catch? Is that in part because the species has been fished over, beginning in the chalk streams of England since the 1500s?
That’s when Dame Juliana Berners wrote “Treatyse of Fysshynge with an Angle,” the first book on fly fishing.
Since anglers have been fishing for brown trout in England for over 500 years, does that mean the species has become difficult to catch because of hundreds of years of fishing pressure? Have browns learned to become wary over time, or are they just naturally very wary creatures?
Continuing this theme, what about rainbow trout, cutthroat trout and brook trout, regarding their wariness and how they feed?
I believe that anyone who has fly fished for a period of time and has had the opportunity to fish for brown, rainbow, cutthroat and brook trout will admit that browns are the most difficult to catch.
Again, is that because they are naturally very wary, or is it because they have learned to adapt to all the various forces that want to catch or eat them? Comparatively speaking, rainbow trout, cutthroat trout and brook trout are easier to catch and have not changed their feeding behavior as brown trout have. Is that because they are not as smart as brown trout—or is it because they have only been fished for since the 1800s, and have not found it necessary to adjust their feeding behavior accordingly?
Is it that they have not been harassed by outside forces as long as browns have?
What I can say about cutthroat trout, and this is based on a reputable authority: Cutthroats that inhabit Flat Creek, outside of Jackson Hole, WY, are very easy to catch when the season opens on August 1. However, after about two weeks of sustained angling pressure, those trout become very difficult to catch. The question then remains, do the various species of trout learn to change the way they feed in order to survive, or is this a genetic mechanism that helps them survive?
Trout have a brain about the size of pea, so it’s hard to understand that brown trout in particular can modify their behavior through a thought process that borders upon reason. Yet there is research that confirms this phenomenon.
Studies conducted by the Institute for Environmental Research and Education found that brown trout can adapt their feeding behavior, are able to learn, have spatial awareness and have personalities. So if our observations and the research are correct, brown trout do have the ability to change their behavior via some level of thought process! Who knew?
In the meantime, we continue to fly fish, observe and wonder why our spotted friends do what they do and are so difficult to catch. I guess if we had all the answers, trout, especially brown trout, would be as easy to catch as bluegills, and that just would not be much fun!