By the time they are an adult, bull trout can measure over 2 feet in length and weight over 20 pounds. Their large size lends itself to them being the apex predator in the lakes and rivers of the upper Yakima River Basin. However, as young fish they are an important part of the food chain as prey. Bull trout begin their lives living in gravel in rivers, eventually emerging to feed on insects and plants. When they do, they provide food for a wide variety of predators including fish, reptiles, birds and mammals.
Big Fish, Little Fish
While rearing in protected waters, bull trout are susceptible to larger fish including sculpin and cutthroat trout. They are also eaten by larger bull trout, who generally begin feeding on other fish in their first year of life. In addition, because of the degraded quality of many of the streams and rivers that bull trout rear in, there often isn’t enough sheltered habitat to protect them from high runoff. This pushes young bull trout out into lakes where it is hard to hide from lake dwelling predators such as burbot, pike minnow and adult bull trout. Food sources for young bull trout are also different than what is in rearing streams, making their survival even more challenging.
Not Just a Garden Companion
Although we typically think of them as garden critters, garter snakes are a voracious predator in rivers and streams. Garter snakes take advantage of the late summer months when water levels lower. During this time bull trout and other fish become stranded in pools or are forced into areas of slower, shallow water. Garter snakes swim, searching under rocks and through gravel for an easy meal. When we are out in the field it is not uncommon to see several garter snakes scattering away as we pass by these pools and shallow areas. Dewatering in upper Kachess River and Gold Creek further decreases bull trout’s chances of survival because there is less protected habitat and what is available often isn’t sufficient.
Other predators include osprey and otters, which tend to feed on larger fish, but will eat smaller fish when they are easily accessible. Some of the pools that rearing bull trout become trapped in have no woody debris to provide shelter from larger animals such as these.
Rebalancing the Food Chain
Like their salmon relatives, the odds of bull trout becoming an adult are small, but are even less now due to habitat degradation from activities such as logging, mining, road construction and housing development. In a healthy food web, bull trout play important roles as both predator and prey. But, human-caused impacts have created an unbalanced food web causing bull trout to be more vulnerable to predation than they were previously.
Bull trout are culturally significant for the Yakama Nation. They are also important as an indicator species – their need for cold, clean water helps scientists monitor climate change and its potential effects on all salmonids living in the upper Yakima River Basin.
Through our work, which is supported by the Yakima Basin Integrated Plan (YBIP), we are trying to restore the streams and rivers used by bull trout to ensure their survival in the upper Yakima River Basin. We could not do this work without our partners and YBIP, which provides funding and technical assistance for the partners of the YBIP Habitat Subcommittee to support these important projects.
**Bull trout photo by Josh Rogala