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 trutta, (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−1) 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 ms−1 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.