UW Aquatic & Fishery Sciences Quantitative Seminar
School of Aquatic and Fishery Sciences, University of Washington
Which assessment configurations perform best in the face of spatial heterogeneity in fishing mortality, growth and recruitment: A case study based on pink ling in Australia
Most fisheries stock assessment methods are based on the assumption that fish are homogeneously distributed across the area being assessed or that fish movement is such that local fishing pressure does not lead to heterogeneous patterns of abundance. However, this assumption is seldom valid in practice. Seven alternative approaches for conducting assessments in the face of possible spatial variation in fishing mortality, growth and recruitment are identified. These approaches range from ignoring spatial structure and pooling data spatially to conducting a multi-area assessment that accounts for spatial variation in biological and fishery processes. These seven approaches are tested using simulations based on the actual situation for pink ling off southeast Australia. Spatially aggregated assessment configurations provide biased estimates of initial and final spawning biomass, as well as of the ratio between initial and final spawning biomass, but assessment configurations which allow for spatial structure can provide imprecise estimates. Best practice in terms of selecting the appropriate structure for an assessment in the face of possible spatial heterogeneity in biological and fishery parameters is to conduct sensitivity analyses based on several model configurations.