The performance of sea trout,Salmo trutta L., stocks from the Burrishoole system western Ireland, 1970–1994.

Abstract Since 1975, with partial recoveries in 1979 and 1984–1986, the numbers of finnock and adult sea trout, Salmo trutta L., in the Burrishoole system, western Ireland, have declined. The population decreased sharply from 1987, and collapsed in 1989 and 1990. Finnock were virtually absent in 1989 and one-year maidens equally so in 1990. Sea trout smolt recruitments from 1992 to 1994 were the lowest recorded since 1970. The modal fork length of finnock decreased from 28 cm in 1987 to 26 cm in 1990. Up until 1989, the percentage return of smolts, as finnock, ranged from 11.4 to 32.4%. In 1989 a minimum was reached at 1.5%, with values of 10.0, 3.7, 7.4 and 9.9% from 1990 to 1994. Marine survival of smolts, to total first return to fresh water, historically ranged from 19 to 66%. Survival dropped to 1.8% in 1989. Observed changes in the structure of the sea trout population and the collapse in marine survival suggest that the current west of Ireland sea trout problem is based in the marine habitat.