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Marine survival difference between wild and hatchery-reared steelhead trout determined during early downstream migration
- Melnychuk, Michael C., Korman, Josh, Hausch, Stephen, Welch, David W., McCubbing, Don J.F., Walters, Carl J.
- Canadian journal of fisheries and aquatic sciences 2014 v.71 no.6 pp. 831-846
- Oncorhynchus mykiss, acoustics, adults, freshwater, hatcheries, juveniles, models, mortality, rearing, rivers, salmon, smolts, sodium hydroxide, telemetry, wild fish, British Columbia
- We observed large survival differences between wild and hatchery-reared steelhead trout (Oncorhynchus mykiss) during the juvenile downstream migration immediately after release, which persisted through adult life. Following a railway spill of sodium hydroxide into the Cheakamus River, British Columbia, a short-term conservation hatchery rearing program was implemented for steelhead. We used acoustic telemetry and mark–recapture models to estimate survival of wild and (or) hatchery-reared steelhead during 4 years of the smolt migration, with both groups released in 2008. After adjusting for estimated freshwater residualization, 7%–13% of wild smolts and 30%–40% of hatchery smolts died in the first 3 km of the migration. Estimated survival from release to ocean entry was 71%–84% for wild fish and 26%–40% for hatchery fish and to exit from the Strait of Georgia system was 22%–33% for wild fish and 3.5%–6.7% for hatchery fish. A calculated 2.3-fold survival difference established during the downstream migration was similar to that after the return of adult spawners, as return rates were 8.0% for wild fish and 4.1% for hatchery fish. Contrary to current understanding, a large proportion of salmon mortality in the smolt-to-adult period, commonly termed “marine mortality”, may actually occur prior to ocean entry.