Predicting the Biological Impact of Competitive Fishing

We used literature data to derive general Leslie matrix models for the population dynamics of largemouth bass Micropterus salmoides and walleye Stizostedion vitreum. With these models, we predicted the impact competitive fishing has on the joint management objectives of maintaining population abundance and population size structure. Our results showed that the amount of fishing that was sustainable without causing population decline increased with intrinsic population growth rate, but was only slightly affected by individual growth rate. Constraints on fishing mortality imposed by population size structure objectives, however, were determined primarily by individual growth rate. Comparison between species indicated that largemouth bass could support greater fishing mortality than walleye for the same level of population growth rate. This occurred because of differences in the maturation schedules of the two species relative to the age and size at which fish become legal to keep for entry into tournaments. For both species, population size structure objectives were of greatest importance when the intrinsic population growth was above approximately 20% per year, a level of growth that appears well within the range of natural populations of largemouth bass and walleye. Thus, we suggest that considerations of population size structure may often be more important than population abundance in determining strategies for managing lakes with competitive fishing events.