The Lake Where You Live

Fishing for walleyes on a Canadian lake, my brother Steve and I observed something puzzling.

We’d anchor over a spot the resort owner had marked on GPS and deploy minnow-tipped jigs. For five or ten minutes, nothing would happen. Then one of us would get a bite, starting a flurry: a bite every time, for five minutes, fifteen, thirty.

We speculated on the reason for this pattern. Was some chemical signal involved? Did one walleye capturing prey release a pheromone and trigger a feeding response in others? We didn’t and still don’t know. We do know that pheromones play various roles in fish behavior.

Pheromones are chemical agents by which members of animal species communicate. The pheromone molecules are soluble in water and diffuse through it. Fish detect them by way of special receptors in the nasal cavities. 

Though pheromones are released in tiny concentrations, members of the species recognize and respond to them. For example, pheromones play a role in reproduction, enabling fish to attract mates and synchronize spawning.

Others, known as alarm pheromones, help fish avoid predators. A small fish injured by a predator might release a pheromone that signals others of its species to flee or seek cover. I’ve wondered if this might be at work at times when the appearance of a musky shuts down an active walleye feeding spell here on Birch Lake.

Even more interesting, researchers at UW-Madison have found that pheromones released during prey by walleyes on yellow perch caused the perch to grow significantly faster. The evolutionary benefit of more rapid growth is that larger fish are more difficult for predators to eat.

The researchers believe the pheromone might be released from the skin of the perch or be contained in the walleyes’ urine or feces. Or it could be a stress hormone leaking from the perch into the water. 

“The surviving perch grow twice as fast, because they are smelling something that signals the presence of predators,” researcher and senior animal scientist Terence Barry reported in an article on the Wisconsin Alumni Research Foundation website. 

“We do know that chemical communication is widespread in fish. When a male smells a female that is ready to spawn, it gets a surge in the pituitary hormone gonadotropin, which binds to the testes, causing them to produce testosterone, leading to sperm production. We think a similar thing may be going on here…”

Were pheromones responsible for what my brother and I observed in Canada? Possibly. Walleyes are mainly sight feeders, but in low-visibility conditions, such as the deeply tannin-stained water in which we were fishing, the fish might have to resort to other means of prey detection. Even so, there could be explanations other than chemical voodoo. 

Maybe it was simply a matter of a walleye school arriving on the scene, encountering our minnows, and engaging in a sort of feeding frenzy. In any case, one of the joys of angling is stopping to contemplate the mysterious behaviors of the fish we pursue.

Ted Rulseh, a writer, author and advocate for lake protection, lives on Birch Lake in Oneida County. Visit him and his blog at https://thelakeguy.net.