Survival of Brown Trout (Salmo trutta L.) Stocked as Summerlings and Autumn Fingerlings in Two Northern Ireland Lakes

The survival of 0+ brown trout, spray-marked with fluorescent pigment and stocked in two angling lakes as summerlings and autumn fingerlings, was assessed by netting exercises. About twice as many autumn fingerlings as summerlings survived the first winter after stocking, and in one lake the percentage survival of the two groups was estimated at 31.0% and 15.2% respectively. Survival to age 2+ was estimated to be in the range 5.7–9.7% for summerlings, and from 15.1% to 16.6% for autumn fingerlings. The best survival for both groups was obtained in the most productive lake, where condition factors and growth rates were the highest. The results were assessed in economic terms, and the cost per 2+ fish in each lake was more expensive from both summerling and autumn fingerling stocking than from direct introductions of fish-farm, two-year-old trout.