Postrelease Performance of Acclimated and Directly Released Hatchery Summer Steelhead into Oregon Tributaries of the Snake River

Abstract

In a study using 14 paired‐release groups over 10 release years, we compared the performance of hatchery summer steelhead Oncorhynchus mykiss that were acclimated as smolts (AC) for 16–57 d before release into ponds supplied with ambient stream water with that of fish trucked from the hatchery and directly released (DR) into Spring, Deer, and Little Sheep creeks in northeastern Oregon. After releasing the fish into streams, we monitored out‐migration travel times and survival to Lower Granite Dam (LGD) on the Snake River using freeze brand marks or implanted passive integrated transponder tags in a subsample of each release group. Across all release groups, travel time was significantly slower for AC fish (34.7 d) than for DR fish (31.8 d), though there was no significant difference in survival probability to LGD. We used recoveries of coded wire tags to estimate smolt‐to‐adult survival (SAS) and a stray rate index (SRI) for the AC and DR strategies. Across all release groups, SAS was 33% higher and SRI 42% lower for AC steelhead. At each release site acclimation increased average SAS by at least 11% and decreased SRI by at least 16.5%. We found a significant, negative linear relationship between travel time to LGD and SAS; however, there was no significant relationship between survival to LGD and SAS, which implies that judgments about the success or failure of a novel rearing or release strategy should not be made based on out‐migration survival. Acclimating juvenile steelhead produced significantly higher SAS and lower SRI in the hatchery program we evaluated; however, our results are not consistent with those of other steelhead acclimation studies.

Experimental Evidence for Olfactory Imprinting by Sockeye Salmon at Embryonic and Smolt Stages

“…Together, these results suggest that longer odor exposure periods may facilitate successful imprinting and that acclimation for a period of time prior to release may improve homing fidelity. However, previous studies on the importance of acclimation timing for successful imprinting in steelhead and Chinook Salmon have produced mixed results, suggesting that homing site fidelity may improve with acclimation (e.g., Clarke et al 2010) or have no effect (e.g., Kenaston et al 2001;Clarke et al 2016).…”

“…Indeed, many studies of salmon released into natural river systems suggest that relatively short exposure time is sufficient for fish to learn site-specific olfactory cues that they can utilize for successful homing. For example, Coho Salmon held as smolts for 36-48 h in spring water prior to release homed accurately to this water source as adults (Jensen and Duncan 1971), and Snake River Sockeye Salmon and steelhead smolts released directly into tributaries migrated quickly downstream but most successfully imprinted and homed to their release site (Hebdon et al 2004;Clarke et al 2010). Together, these results suggest that longer odor exposure periods may facilitate successful imprinting and that acclimation for a period of time prior to release may improve homing fidelity.…”

Density Effects on Subyearling Fall Chinook Salmon During Hatchery Rearing in Raceways with Oxygen Supplementation and After Release

“…Yet in our study the seemingly poor imprinting and high stray rates occurred across all treatment groups, which provide evidence that high density rearing did not contribute to the problem. Acclimation also apparently did not improve imprinting and reduce straying as it has in other studies (Garcia et al 2004;Clarke et al 2010), although our study did not include a direct stream release group necessary to definitively reach such a conclusion. Thus, we speculate that the high straying rates were most likely due to a mismatched timing between when fish were physiologically prepared for imprinting and when they were exposed to Umatilla River water.…”

Ingestion of PIT Tags by Hatchery‐Reared Juvenile Steelhead and Subsequent Detection at Main‐Stem Dams in the Columbia River Basin

“…Biologists and statisticians have frequently used the Cormack–Jolly–Seber (CJS) mark–recapture model to estimate joint apparent survival and detection probabilities for Pacific salmon during their migration through the hydroelectric dams of the FCRPS (e.g., Burnham et al 1987; Skalski et al 1998; Zabel et al 2005; Clarke et al 2010). A fundamental assumption for mark–recapture models like the CJS is that the tags or marks are not lost (Burnham et al 1987).…”