What do trout see, hear and smell?
I have had a tough day or two on my favorite water recently. The water has been low and clear with a painfully slow flow, which is not unusual for this time of year. With the water low and slow, there is a noticeable ripple effect caused by my wading upstream to one of the ‘hot spots’. So, I tend to halt just downstream of the spot, wait a few minutes for the wake I have created to disappear and then begin casting upstream to the fish.
On this water the ability to get close without spooking the fish is tested. Days like this make it difficult to get close-ish and not have them be wary. There are fishermen on this water nearly every day (and this spot gets plenty of daily pressure), so after a few weeks even these stockers become pretty tentative.
When water flow or current is better, the distraction can be favorable in approaching the fish. Wind and rain disturbance on the surface of the water can also be favorable in this regard. But after fishing this water for many years I know one thing to be certain, gin-clear water and blue bird skies can severely hamper the prospects for hooking up. Generally, if you can see the fish, they can also see you!
And it is clear that trout can see very well. How else can they pick up on a size 22 nymph? Fish can cue in on food quickly and are known to try anything that passes them, especially recently stocked fish that are acclimatizing to their new aqua environment. Low flow or current gives fish time to inspect what is heading their way, so the fly and presentation had better look natural.
I have often wondered about a trout’s sense of hearing. I have had serious strikes from trout that have risen to a large-sized terrestrial fly that is plopped on the water surface with some force. I find it hard to determine if they are prompted by the sound or by the vibration of that terrestrial pattern hitting the water.
I recently listened to an Orvis Fly Fishing podcast by Tom Rosenbauer featuring an interview with Dr. Russ Carpenter, a Stanford neurologist. His experience studying the brains and senses of fish make him a compelling and intriguing authority on this topic.
As it relates to the trout’s sense of hearing (and I am generally referring to rainbow trout in this instance), Dr. Carpenter believes that trout are accustomed to how the water carries sound and are in tune to it. He is less clear on whether they can distinguish sounds that are transmitted. The vibration certainly alerts them to a sound and the possible direction of that sound, and it is quite likely that distraction can interfere with that understanding.
This probably explains somewhat the advantage facilitated by increased current in my favorite water, as well as surface disturbance created by wind or rain. The distraction may make them less wary, but also the speedier water gives the trout less time to decide whether a fly offering is worthy or not. It also may suggest that fish may not necessarily associate cleats or studs clacking through a riffle as being a fisherman, versus a deer walking through the stream or structure breaking free and moving through the current.
It is certain that trout have an acute sense of smell. According to Dr. Carpenter pheromones play a role in fish lives through scent – urinating fish send chemical information to other fish as to mating or aggressive tendencies. So, it is likely that fish will pick up on unnatural scents introduced into their habitat.
What that suggests to me is that leaving sunscreen or bug spray on my hands and then allowing that residue to touch my fly line is likely going hamper my prospects for hooking up, especially if dead-drifting my line over top of the fish. So, I will probably start applying the sunscreen with the back of my hand going forward.