Yield per Recruit Analysis Under Spatial Heterogeneity in Growth and Fishing Effort

Yield per recruit (Y/R) models typically make no allowance for heterogeneity in fishing mortality, natural mortality or growth across the stock area.  Areas with higher growth and/or lower natural mortality rates should be fished less than other areas in order to optimize Y/R, but these areas may be attractive to fishermen, especially if they are also areas of high recruitment, and so in some cases may be fished harder.  The realized Y/R from the fishery may therefore be different than that calculated assuming spatially uniform fishing mortality and life history parameters.  Yield per recruit models are developed that simultaneously account for spatial heterogeneity in growth and fishing effort, and are applied to the U.S. Atlantic sea scallop (Placopecten magellanicus) fishery assuming, alternatively, the observed, uniform, or optimal distributions of fishing effort.  In this example, the mismatch between observed and optimal fishing effort distributions results in lost Y/R.  This study indicates that spatial management may be required to optimized yield, especially when adults are sedentary.