Linking the dynamics of harvest effort to recruitment dynamics in a multistock, spatially structured fishery

A freshwater sport fishery that targets hundreds of geographically isolated stocks is simulated by combining a model of angler behavior with a model of rainbow trout (Oncorhynchus mykiss) population dynamics. Ideal free distribution (IFD) theory, which suggests that angling quality will be similar on all lakes, is used to drive angler effort distribution. Model parameters are based on creel survey data from 53 lakes and empirical relationships between growth, survival, and density derived from whole-lake density manipulations on nine lakes over a period of 10 years. We compared angling quality, population density, fish size, and yield under unfished conditions, harvest rates that maximize sustained yields (MSY), and an IFD equilibrium driven by angler behavior. The IFD equilibrium rarely maximized yields. Stocks with high MSY angling quality are overexploited at the IFD equilibrium because anglers move to take advantage of exceptional angling opportunities. These stocks would often be viewed as more resistant to harvest pressure because they have higher stock productivities and habitat capacities. However, in our model, they are systematically overharvested because their high fish density attracts excessive angling pressure. Conversely, stocks with low MSY angling quality are underexploited because anglers move to take advantage of better angling quality on other lakes.