Comparing Current and Alternative Regulations in a Declining Walleye Fishery By Visualizing Tradeoffs Between Spawning Biomass and Yield

Regulatory options for the walleye fishery on Mille Lacs Lake, Minnesota, were compared by evaluating spawner-yield tradeoffs on a per recruit basis. Following a court settlement which established shared State and tribal fisheries for walleye, biologists devised an assessment and management process for estimating population size, determining allowable catch, selecting regulations, and dealing with quota overruns. A variety of regulations to control harvest were tried over the last 15 years.  Recent population declines prompted managers to rethink the goals and management strategy to consider both yield and conservation of spawners. It is not known how much spawning biomass is needed to maintain acceptable recruitment. But, clearly, some harvest policies are uniformly superior to others in that they provide more spawners and more yield. In most of our comparisons, increases in either spawners or yield can be achieved only by accepting a reduced or a constant level of the other parameter. A graphical procedure allows managers to visualize a great deal of information in a compact and intuitive format and select candidate regulations. The analysis requires estimates of size- and sex-selectivity of the fishery and of voluntary release of fish by size. These are obtainable from tagging studies and creel surveys.