Vail Curious Nature: Trout don’t go with the flow
Vail, CO Colorado
Close your eyes and imagine the location in which you were born. Would you be able to navigate your way back to the exact place of your birth (hospital room and all) without the use of pictures, maps, compasses, or even your beloved GPS unit in your car providing you with turn by turn directions? Brown trout is one species that masters this navigational challenge annually as they travel upstream and return to their birthing grounds in order to spawn.
Each October, these determined fish do not surrender to the flow, but rather fight against it as they leave deep pools in lakes and rivers to migrate upstream to the shallow, well-oxygenated, and gravel lined rivers in which they were born. Sometimes these determined trout travel many miles and battle many obstacles, such as predators, waterfalls, and boulders to reach their destination. You may be wondering just how these red and brown spotted fish are able to navigate their way back to the place in which they hatched from eggs. They were just little fries then, how would they ever remember how to get back to that location? Perplexing indeed! While scientists are not completely sure how fish find their way, they think the brown trout’s navigational expertise may be a combination of orienting themselves with an internal compass, recognizing the position of the sun, identifying particular landmarks, and using the old sense of smell.
Reaching the spawning site is merely half the battle. The female then must attract a suitable male’s attention. In much of the animal kingdom, the male expends the energy to attract the female. Bull elk belt a resounding bugle that clues the female into its approximate size and social rank among other bulls in the area. The female then chooses a bull of her liking. Similarly, male grouse will strut their stuff as they fan their tail feathers, inflate their air sacs, and make popping noises to attract a female. The female observes the male in action and decides whether or not she digs his style. When it comes to brown trout, although the males coloration intensifies greatly which may help to attract a female, males play hard to get acting rather aloof to females. It is not until a female begins to initiate her egg laying ritual that a male decides to become part of the action.
Upon arriving at the spawning site, she will swim sideways and beat her tail on the bottom of the river to create a saucer shaped depression in the gravel, called a redd. This is where she will lay her eggs. This very act stimulates the male, who will then swim alongside the female, quivering his body. This in turn excites the female. Romance is in the air … or in the dissolved oxygen with this case! As the male increases the frequency and intensity of his quivers, the female prepares to lay her eggs. She indicates to the male that the time has come as she opens her mouth to a gape and releases her eggs into the gravely depression made earlier. The male follows suit by simultaneously depositing his milt on the eggs, fertilizing them. The female moves further upstream where she again beats her tail to loosen gravel, burying her fertilized eggs while also creating another redd in which to lay more eggs. She continues this process until her clutch of 4,000 to 12,000 eggs are laid and covered. Both male and female then abandon the eggs and head back home. The eggs develop over the winter months and hatch in the early spring.
While most of the year brown trout are rather elusive and conceal themselves well in deep pools, stream debris, undercut river banks, and rocks, spawning season makes the brown trout far more accessible to anglers. As they migrate upstream to their spawning grounds, they become more territorial and aggressive, attacking anything that comes near them in the water, including cleverly tied flies resembling big, fat, juicy looking aquatic macroinvertebrates. However, some anglers out there disagree with fishing during spawning season claiming the fish are far more vulnerable since spawning is quite stressful on these river runners. Whether you choose to fish during this time of brown trout abundance is up to you, but do take a moment to appreciate the trials and tribulations these fish undergo each year as they do not surrender to the flow while searching for that special spark under the water to produce the next generation of brown trout.
Beth Garrison, curriculum specialist for Walking Mountains, develops hands-on and place-based elementary science curriculum as part of the Integrated Science Study program. When she is not writing lesson plans, she can be found making thimbleberry pie, falling off her mountain bike, or exploring the mountains with her dog.