Survival of stocked Atlantic salmon and coarse fish and an evaluation of costs

The stocking of fish represents a major activity in current fisheries management practice. To maximise benefit to the environment in general and to fisheries in particular, optimal stocking strategies need to be developed. Examples from two studies, one involving Atlantic salmon, Salmo salar L., and the other involving three coarse fish species, are used to illustrate how such strategies might be developed. Atlantic salmon fed fry (age 0+) were stocked into eight streams in the North West of England at densities ranging from 1 to 4 m(-2) over a period of up to 3 years to evaluate survival to the end of the first and second growing periods. Survival to the end of the first growing period (mean duration 108 days) varied between 1.2 and 41.3% with a mean of 20.45% and CV of 0.53. Survival from the end of the first growing period to the end of the second growing period (mean duration 384 days) ranged from 19.9 to 34.1% with a mean of 26.3% and a CV of 0.21. Hatchery-reared roach, Rutilus rutilus (L.), chub, Leuciscus cephalus (L.) and dace, Leuciscus leuciscus (L.), were stocked into four rivers to determine the optimal age and season which would maximise survival over a 6-month post-stocking period. Post-stocking persistence within the stocked reaches was generally low; the highest level of persistence was estimated at only 33.8%. However, most of the estimates of persistence were considerably lower and (in practical terms) approached zero in several instances. The analysis indicated that river-specific factors are important in determining the success of stocking exercises. The survival estimates derived from these two studies were compared with other published estimates.