The influence of piscivory on life history traits of brown trout

Brown trout in Lake Femund migrated from the nursery streams mainly at 2 ye ars old, but ranging between 1 and 8 years. Brown trout switched to piscivo ry from 3 years onwards, and a body length of 17.5 cm, according to back ca lculation from scales. Fast growers switched to piscivory at a younger age and smaller size than slow growers. The most slow-growing trout switched to fish feeding at 9 years old and a mean body length of 36 cm. The growth of the invertebrate feeders was almost rectilinear to c. 45 cm and 11 years o f age. Switching to a fish diet induced increased growth rates. Age at sexu al maturity increased with the age at which the fish became piscivorous. Th e invertebrate feeders matured at an age similar to that of the most fast g rowing piscivorous trout. The mortality rate of sub-adults and adults did n ot differ significantly between fish and invertebrate feeding trout. Longev ity of piscivorous trout was estimated at 11 years and of invertebrate feed ers at 10 years. (C) 1999 The Fisheries Society of the British Isles.