Production in a Lacustrine Brown Trout Population with Large Recruitment Potential and Low Natural Mortality: Implications for Management

This is the authors' abstract. We don't add key points for this paper.

The annual production of different age-classes of an allopatric population of brown trout Salmo trutta in a small lake subject to increased fishing mortality was estimated for four successive years. Individuals in the initial population were characterized by stunted growth. Annual growth rates did not increase when population biomass decreased from 15.6 kg/ha in 1985 to 9.4 kg/ha in 1988, and theoretical maximum lengths remained in the range 23.8–25.0 cm throughout the study. Total annual production increased only from 3.4 kg/ha in 1985 to 4.3 kg/ha in 1987, although the turnover ratio (production : biomass) increased from 0.22 to 0.44. The increase in turnover ratio was due to an increased immigration of juveniles from the nursery streams. Food resources made available by a reduction in the density of old, mature fish were probably consumed by the increased number of juveniles, rendering no food surplus for the sustained growth of the remaining mature fish. The results reported here and their causal mechanisms may have important management implications. In order to increase growth rates and production of mature fish in populations with large recruitment potentials and low natural mortality, exploitation has to be directed mainly towards the recruits.