Spawning Season Survey

We were curious what kind of fall spawning activity was taking place in the upper river, since redd counts are not conducted in these reaches. In particular, we were interested in whether we could identify the spawning areas of brown trout, which have struggled these last few years.

Thanks to the generosity of Melrose rancher & BHRF Board Member, JM Peck, we were able to fly the entire river back in October and get a bird’s eye view of spawning redd locations & densities - noting what we saw and sharing those observations with biologists from Montana Fish, Wildlife, & Parks.

It was a fantastic opportunity to view the entire watershed from above and gain insight into fall spawning locations in the Big Hole. Incredibly, for a brief time when the sun was perfectly overhead, individual fish – some of significant size – were visible from the air, suspended over the cleaned gravel.

The Big Hole River above Wisdom

Photo Credit: Brian Wheeler

Brown trout will move to find the right habitat for their reproductive efforts, which is dependent on good gravel or substrate in which to lay their eggs. Often, this particular habitat is found in shallow, faster-moving tailouts in the mainstem of the Big Hole. The female will prepare the gravel in a redd by fanning it with her tail, cleaning out the algae and sediment to allow space for the eggs to settle in. This behavior also ensures that the eggs get adequate oxygen from the running water. As the female deposits eggs onto the redd, the male will be right there beside her attempting to fertilize them – we call these “spawning pairs”. They will then be covered up by gravel by the female for the winter and with some luck, will hatch early in the spring.

While these preferred spawning locales are excellent for observing this fascinating and physiologically taxing natural phenomenon, it also exposes these fish to overhead predators and unethical anglers who target fish in such sensitive locations. Sexual maturity is not typically reached until 3-4 years, meaning that it is only the older resident brown trout engaging in the production of future generations. Thus, it is incredibly important to avoid fishing to spawning fish as they are already stressed and only a small percentage of them are actively engaged in reproduction. It is also critical to avoid walking over the cleaned gravel where they spawn, since that can result in the destruction of eggs; next season’s young-of-the-year. The importance of this type of self-regulation by anglers cannot be stressed enough.

Because it is such a sensitive time for brown trout, especially on the heels of low, warm water throughout these past few drought years, the Big Hole now has a spawning season fishing closure from BLM Maidenrock FAS to Brownes Bridge FAS between October 1st – March 31st to protect these fish and to study whether the closure has a positive impact on recruitment of young fish.

A pair of upper Big Hole spawning redds

Photo credit: Wade Fellin

Photo credit: Wade Fellin

Photo credit: Wade Fellin