Cattle Trampling of Simulated Bull Trout Redds

Abstract

Listing of the bull trout Salvelinus confluentus under the Endangered Species Act and concerns over livestock stepping on bull trout redds have led many U.S. Department of Agriculture Forest Service managers to remove livestock from bull trout spawning areas once spawning begins. While this policy has extensive ramifications for livestock producers who graze their cattle on national forests, a lack of data precludes evaluation of the benefit of livestock removal to bull trout populations. To fill this information gap, we assessed the probability that cattle would step on simulated bull trout redds in grazing allotments within the Little Lost River drainage in Idaho. Bull trout redds were simulated using clusters of clay shooting targets. Simulated redds were placed in streams within three grazing pastures where bull trout have historically spawned or currently spawn. During the 14–21-d grazing period, 15–83% of the simulated redds were affected by trampling. When the control period was standardized to the same time period as the treatment, cattle were found to be responsible for affecting 12–78% of simulated redds and breaking 6–49% of the clay targets. Impacts were higher in pastures where cattle stocking intensity was higher, but impacts were also determined by site conditions adjacent to the simulated redds.