Abstract
Demographic and environmental factors can influence the spatial distribution of fish populations, potentially affecting the timing, location, and magnitude of harvest. Quantifying these relationships can be complicated, if their effects vary spatially over a population’s range or are non-additive (i.e., interactive), where one factor mediates the effect of another. Toward understanding the relative influence of demographic and environmental factors on fishery harvest in large freshwater lakes, we used varying-coefficient generalized additive models to explore the existence of non-additive, spatially-dependent effects of adult population size and thermal conditions on recreational harvest patterns of Lake Erie walleye (Sander vitreus) during 2006-2015. We identified nonlinear, additive, and generally positive effects of thermal conditions and adult population size on harvest rates. Their effects were, however, spatially-dependent, the accounting of which can help explain inter-annual and intra-annual variation in lake-wide harvest rates. Specifically, harvest rates increased more with increasing cumulative degree days in the eastern portion of the central basin, especially offshore, relative to the rest of the study area. Harvest rates also increased more with increasing walleye population size in the southwest portion of the west basin and the middle of the central basin compared to other study areas. As in marine ecosystems, our findings demonstrate the benefit of using modeling approaches that consider the spatial dependency of harvest rate on demographic and environmental factors to understanding broader harvest dynamics in large lakes. Their use could help managers and policy-makers ensure the sustained use of valued freshwater fish populations amidst demographic and environmental change.
Published Version
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