Brook Trout Distribution in the Spring Branch Tributaries of the East Little Walla Walla River 2011 Assessment Report

Invasive, self-sustaining populations of Brook Trout (Salvelinus fontinalis) have become established in basins throughout the Pacific Northwest where they may displace and compete with native salmonids (Dunham et al. 2002; Meyer et al. 2006). The Bull Trout Draft Recovery Plan (USFWS 2002) identifies the presence of Brook Trout within Bull Trout Core Areas as a major threat to the long-term persistence and eventual recovery of populations in the Columbia River Distinct Population Segment.

Historically, resource managers believed that Brook Trout did not reside within the Walla Walla River Basin. However, the Confederated Tribes of the Umatilla Indian Reservation (CTUIR) documented a small, established population of Brook Trout occupying the East Big Spring Branch (EBSB) of the Little Walla Walla River (ELWWR) near Milton-Freewater, Oregon (Hoverson 2004; Mahoney et al. 2006). In addition, the US Fish and Wildlife Service (FWS) captured an adult Brook Trout in a pond near the headwaters of the EBSB in 2009. The capture of the fish renewed interest among agencies in further investigating the Brook Trout population in the spring branch tributaries of the ELWWR. Before removal, suppression or other management actions could be considered, a better understanding of the population was essential. In August of 2011, the FWS coordinated a multi-agency effort to assess the distribution of Brook Trout in the EBSB, the WBSB and the ELWWR.