An Attempt to Rehabilitate a Collapsed Brook Trout Population by Introducing F₁ Splake to Control Yellow Perch

Abstract

Historically, brook trout Salvelinus fontinalis provided an outstanding sport fishery and lived sympatrically with yellow perch Perca flavescens in East Lake, a 30-ha water body in central Ontario. The fishery collapsed when lake access was improved and cottages were built around the shore in the early 1960s. Annual stocking of brook trout did not improve the brook trout fishery. During the 1980s it became apparent that yellow perch were abundant and small-bodied. Based on historical studies in similar ecosystems, we concluded that the perch were competing directly with, and possibly preying on, the juvenile brook trout. In this study we attempted to reduce the perch population by repeatedly stocking first-generation (F₁) splake hybrids (female lake trout Salvelinus namaycush × male brook trout) over a 7-year period. We hypothesized that the splake would reduce the abundance of yellow perch, which in turn would allow the brook trout population to increase. Stock assessments during the study period (1990–1997) indicated that the yellow perch density declined more than 95% (from approximately 3,400 to approximately 130 individuals/ha). We argue that the splake caused this reduction because routinely stocked rainbow trout Oncorhynchus mykiss and brook trout had failed to reduce the number of yellow perch and the decline coincided with the splake stocking. In addition, concurrent diet analyses indicated that splake were considerably more piscivorous and much more likely to consume yellow perch than were rainbow trout and brook trout. Although the number of yellow perch was greatly reduced, the brook trout population did not appear to increase; nor was there evidence of a decline in the absence of stocking during the manipulation. We propose the following reasons for the lack of a brook trout response: overharvesting, interspecific competition among salmonids or from residual forage species, the brevity of the study period, and genetic introgression with hatchery brook trout.