Hatchery Steelhead Smolt Release Size Effects on Adult Production and Straying

Abstract

Studies have demonstrated higher postrelease survival for larger hatchery steelhead Oncorhynchus mykiss smolts than for smaller ones. However, the ideal release size should also maximize adult returns and minimize interactions of hatchery fish with wild fish. We conducted a study over five release years with paired groups of anadromous hatchery steelhead smolts reared to target sizes of either 90 g (small size) or 113 g (large size). After stream release, we monitored out‐migration travel times and survival to a downstream dam using freeze‐brand marks in a subsample of each release group. Steelhead smolts that out‐migrate quickly may interact less with wild fish. Across all release groups, travel time was about 3 d slower for small‐sized smolts than for large ones, but this difference was not statistically significant, and there was no significant difference in the percentage of brands detected at the dam between the two smolt sizes. Coded wire tag recovery was used to compare smolt‐to‐adult survival (SAS), the number of adults produced per 100 kg of smolts released, and the percentage of adults that strayed. Across all years, large‐sized smolts had an average SAS of 1.31% compared with 0.92% for small‐sized smolts, a statistically significant difference of 42.0%. The average number of adult steelhead produced per 100 kg of smolts released also was higher for the large‐sized group (11.4 adults/100 kg of smolts) over the small‐sized group (10.1 adults/100 kg of smolts), though the 12.8% difference was not statistically significant. Adults originating from large‐sized smolt releases strayed at a rate of 13.1% compared with a 7.9% rate for the small‐sized smolt groups, a difference that was statistically significant. In this study, larger hatchery steelhead smolts had a higher survival after release; however, we found tradeoffs between management objectives associated with maximizing adult production and those aimed at minimizing ecological risks.

Increased harvest of anadromous hatchery steelhead, Oncorhynchus mykiss (Walbaum), through return timing manipulation

“…To compare smolt downstream travel time and survival to Lower Granite Dam, a representative sample from each early strain or standard strain release group (3,600 and 6,900 fish respectively) were tagged with was passive integrated transponder (PIT) tags. Fish from both strains were reared to a target release size of 113 g, a size that maximises post‐release survival of Wallowa Hatchery steelhead (Clarke et al., ).…”

“…The paired‐release study design employed called for progeny from the two strains to be reared similarly at the same hatchery. However, variability in the hatchery rearing experience may affect smolt release size and smolt seaward migration, two factors that influence the imprinting by smolts on their home waters and the subsequent homing behaviour of adults (Clarke, Flesher & Carmichael, ; Tipping, ; Wagner, Wallace & Campbell, ). Therefore, this study also reports on these juvenile metrics.…”

Egg size and growth in steelhead Oncorhynchus mykiss

“…Fork length at age and growth rate at age both appear to have significant effects on early life history of salmonids (Bohlin et al, 1996;Clarke et al, 2014;Henderson & Cass, 1991). For example, Metcalfe and Thorpe (1992) and Perkins and Jager (2011) showed that fish that had faster growth rates were more likely to migrate sooner than slower growing juveniles in Chinook salmon O. tshawytscha and Atlantic salmon Salmo salar L. 1758, respectively.…”

Family variation in surface feeding behavior of steelhead fry predicts growth rate under hatchery conditions

“…Therefore, we are interested in identifying traits that might be under strong selection in salmon hatcheries. The size of hatchery salmon at release is positively correlated with their probability of survival at sea (10)(11)(12)(13)(14)(15). Therefore, a plausible hypothesis to explain rapid domestication is that hatcheries select for physiological or behavioral traits that allow some fish to grow quickly in the unnatural conditions in a hatchery (11,16,17).…”