Influence of Steelhead Trout Stocking Size and Location on Emigration and Adult Returns

Effective stocking programs are an essential part of maintaining most high-quality tributary steelhead Oncorhynchus mykiss fisheries in the Great Lakes, requiring sufficient numbers of stocked fish to survive, imprint, and return as adults. New York's Lake Erie tributaries have long supported popular and economically important recreational steelhead fisheries, attracting anglers from across the country. Recent research has illustrated New York's dependence on "stray" steelhead from other jurisdictions, making New York fisheries vulnerable to other agencies' management decisions. We hypothesized that the limited contribution by New York-stocked steelhead was attributable to poor poststocking survival and imprinting due to the smaller stocking size relative to other Lake Erie jurisdictions. We took an experimental approach to describe how the combination of stocking size and within-stream stocking location interact to influence emigration and adult returns and identify mechanisms that may be driving these relationships, with the goal of identifying stocking strategies that improve adult returns. Stocked steelhead >150 mm total length emigrated from the stream by the end of May; small-size steelhead tended to remain in the stream and exhibited upstream migration. The residual population of steelhead lost body condition and likely experienced high mortality. Adult returns from large-size fish that were stocked 6.4 km upstream were 4.1 times greater than small-size fish stocked upstream and six times greater than fish stocked near the lake confluence (0.8 km upstream). We conclude that many of the steelhead stocked by New York are too small to imprint and emigrate, instead remaining as stream residents that experience poor survival and ultimately make minimal contributions to the adult fishery. Increases in the stocking size of New York steelhead coupled with stocking well upstream of the lake confluence would result in increased adult returns of New York-stocked fish to their streams of origin and improved fishery performance and resiliency.