Post‐ stocking movements and recapture of hatchery‐reared trout released into flowing waters—effect of prior acclimation to flow

Abstract

Hatchery-reared brown trout, Salmo truttu, (F.L., 16-27 cm) were stocked into the Afon Clettwr, Afon Western Cleddau and Afon Dysynni, Wales. The effects of (a) retaining fish caged in the river for 24 h before release, and (b) a period of acclimation to flowing water (up to 0.24 m S-I) in tanks prior to stocking were investigated. Data on percentage recapture and post-stocking movements were obtained from trapping, electrofishing and tag returns. In-stream acclimation resulted in a higher percentage recapture and a more limited dispersion of the fish stocked under low river flow conditions, but had no effect on trout stocked into a river where higher water velocities were experienced. Acclimation, in tanks, to a flow of 0.1 m s-I for 14 days led to higher percentage recaptures, whereas acclimation for only 2 days resulted in fewer returns than for unacclimated fish. No differences in fish distribution within the rivers could be attributed to these acclimation procedures.

The future of stock enhancements: lessons for hatchery practice from conservation biology

“…1999). Similarly, holding brown trout in enclosures for 24 h at the site of release had a positive effect on the number of fish recaptured (Cresswell and Williams 1983).…”

Impacts of in‐stream acclimatization in post‐stocking behaviour of European grayling in a Swedish stream

“…In‐stream acclimatization before release can reduce this stress through adaptation to water currents, natural food, etc. and increasing the period of acclimatization decreases stress and post‐stocking downstream movements in fluvial Arctic grayling (Kaya & Jeanes 1995) and brown trout (Cresswell & Williams 1983; Jonsson, Brännäs & Lundqvist 1999). Whether this also applies to European grayling is not known.…”

Quantitative assessment of a white seabass (Atractoscion nobilis) stock enhancement program in California: Post-release dispersal, growth and survival

“…This is probably a result of the acclimatisation period the fish go through before being released into the wild habitat. Investigators have observed increases in survival with short acclimation periods (<7 days) for stocked fish (Cresswell and Williams, 1983;Jonssonn et al, 1999;Brennan et al, 2006). Fish released from grow-out pens in this study where held for an average of 160 days (range 14-837 days).…”