Consequences of Stocking Headwater Impoundments on Native Populations of Brook Trout in Tributaries

Abstract

AbstractUnderstanding the impact of hatchery supplementation on the genetics of wild fish populations is important for designing and evaluating ecologically sound stocking practices. For species such as brook trout Salvelinus fontinalis, which are a high priority for conservation and restoration in their native range, understanding the potential impacts of stocking on the functional diversity of wild populations is critical. We sought to determine whether brook trout stocked in low‐order reservoirs colonize impoundment feeder streams and if they naturally reproduce and interbreed with established native populations in these tributaries. Analysis of microsatellite DNA allowed us to distinguish hatchery‐origin brook trout and putative native strains among tributaries of three stocked reservoirs and one unstocked stream. Hatchery‐origin fish were found in tributaries of all stocked reservoirs, mixed with native populations; none were found in an unstocked reference stream that supported wild brook trout. Age‐1 brook trout genetically matching a known hatchery strain were found in tributaries of stocked reservoirs, although none of this age were stocked, suggesting that stocked trout have successfully reproduced in these streams. Assignment tests indicated that 4 of the 98 brook trout collected from mixed stocked–native streams were probably hybrids (∼4.1%; 95% confidence interval = 1.3–10.0%). These results suggest that to date the direct impacts of stocking on the genetics of these native populations have been limited but that indirect impacts through competition or similar interactions may still be occurring.Received January 24, 2011; accepted October 13, 2011