Probable Pheromonal Attraction of Sexually Mature Brook Trout to Mature Male Conspecifics

Abstract

Invasions of nonnative species are a lead- ing cause of the loss of populations of cutthroat trout Oncorhynchus clarki in the western United States, but effective control of invasions of species such as brook trout Salvelinus fontinalis are expensive, labor intensive, and not species specific. Because salmonids respond to chemical cues, we hypothesized that pheromonal attrac- tion could be exploited to capture brook trout. We con- ducted two tests as brook trout spawning began in 1999 and 2000 in two streams in Wyoming, using hoop nets seeded with sexually mature male brook trout, sexually mature female brook trout, or no fish. Catches of sex- ually mature fish in both tests were nonrandom (P ? 0.001); traps seeded with sexually mature male brook trout resulted in a disproportionately high number of captures. Catches of fish that were not sexually mature were not significantly different from expected values (P ? 0.075). In the second test, we estimated that 23% of adult fish were captured in hoop nets in 8 d. Catches were biased toward males by 10:1, and once-captured fish were rarely recaptured. We believe that with further refinements, this approach may be useful for sampling or manipulating brook trout and perhaps other salmonid populations. Invasions