We assessed the influence of timing of harvests on an age-structured population by altering the order of the harvest in relation to density-dependent recruitment and winter mortality. To analyze the effects of harvest timing on a general population of stream salmonids with five age-classes, we used three management strategies: no minimum size limits and two minimum size limits with increasing degrees of protection. The effects on population size, yield, age structure, and population stability were analyzed. Harvest timing greatly influenced the mean population size. A low to moderate harvest increased mean population size in cases with strong density dependence. This increase was even greater at low exploitation levels when harvesting occurred before recruitment. Increasing minimum size limits produced improved population sizes and mean size of fish caught, but yield was lower. Mean population sizes differed in relation to combinations of harvest timing, size limits, and levels of exploitation. In cases where mean population sizes were maintained or increased, the population behavior was mainly attributed to an increased survival of recruits and the stabilizing properties that harvesting had on the population dynamics. This suggests that as harvest rates increase, the population harvested will become increasingly even-aged, and there will be a higher drop in yield but not in mean size of the fish caught. Our results have important management implications but are sensitive to relationships for density-dependent recruitment and mortality.
|Journal||North American Journal of Fisheries Management|
|Publication status||Published - 2000|
Subject classification (UKÄ)
- Biological Sciences