THE TROUT (SALMO TRUTTA) POPULATION OF THE AFON CWM, A SMALL TRIBUTARY OF THE AFON DYFI, MID-WALES

摘要

Data are presented from a 10-year (1984 to 1993) study of a Salmo truttra population in the Afon Cwm. a small tributary of the Afon Dyfi, mid-Wales. The stream is a spawning and nursery area for sea trout. Growth of trout within the stream can be summarized by a von Bertalanffy growth coefficient (K) of 0.310, with asymptotic length (1(infinity)) 21.6 cm and with length at age 1 of 7.6 cm. Mean population density in the whole stream varied from year to year between 0.05 and 0.60 0-group trout m(-2) and between 0.05 and 0.70 older trout m(-2). Mean biomass varied, between years, from 0.1 to 3.5 g m(-2) for 0-group and from 1.3 to 10.4 g m(-2) for older trout. Loss between 3 and 5 months of age appeared to be proportionate at about 50 to 60% and instantaneous loss rate from 5 to 53 months of age varied from 0.04 to 0.10 month(-1) and was positively correlated with cohort number at 3 months of age. Production between 3 and 53 months of age varied between cohorts from 3 to 8 g m(-2) live weight.