By the time they are adults, 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 lake and river ecosystems. 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. Furthermore, human impacts have degraded the quality of many of the streams and rivers that bull trout rear in. Consequently there is little sheltered habitat to protect bull trout form high runoff.
High flows push young bull trout out into lakes where they have little chance of survival. In lakes, it is hard to hide from large lake dwelling fish. These include predators such as burbot, pike minnow and adult bull trout. Another issue is finding food. Lake food sources for young bull trout are different than what is in rearing streams. Locating suitable food is unlikely, 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 slower, shallow water. It is a perfect opportunity for garter snakes. They swim, searching under rocks and through gravel, for an easy meal.
When we are out in the field, it is common 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. There is less protected habitat and what is available often isn’t sufficient.
Other predators include osprey and otters. These predators 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 are just that, pools. They have no woody debris to provide shelter from larger animals making them easy prey.
Rebalancing the Food Chain
Like their salmon relatives, the odds of bull trout becoming an adult are small. However, the likelihood is even less now due to habitat degradation. Activities such as logging, mining, road construction and housing development have created negative impacts that remain today. Climate change is a factor as well. Hotter, drier summers and lower snowpacks lead to less water in the rivers.
In a healthy food web, bull trout play important roles as both predator and prey. But, human-caused impacts and climate change are creating an imbalance. The result is bull trout are more vulnerable to predation. And while we cannot directly address climate change, we can human impacted streams. Through our work, we are trying to restore the streams and rivers used by bull trout. By doing so we hope to ensure their survival in the upper Yakima River Basin.
Bull trout are culturally significant for the Yakama Nation. They are also important as an indicator species. Bull trout’s need for cold, clean water helps scientists monitor climate change and its potential effects on all salmonids living in the upper Yakima River Basin.
We could not do this work without support. Our partners work with us on the ground to survey, monitor and rescue bull trout. Additionally YBIP provides funding and technical assistance for the partners of the Yakima Basin Integrated Plan (YBIP) Habitat Subcommittee to support these important projects.
**Bull trout photo by Josh Rogala