Spatiotemporal index standardization improves the stock assessment of northern shrimp in the Gulf of Maine Canadian Journal of Fisheries and Aquatic Sciences

Estimated trends in relative stock abundance are a primary input to fish stock assessments. Accurate and precise estimates are essential for successful conservation and management. Scientifically designed data collection ensures that estimates of relative abundance are unbiased. However, the statistical efficiency of a design-based estimator may be low under certain circumstances. We apply a recently developed spatiotemporal model that incorporates habitat variables to estimate a model-based abundance index for northern shrimp (Pandalus borealis) in the Gulf of Maine. We contrast this spatiotemporal index with a classical design-based index and evaluate the impacts of differences between the two abundance indices on the stock assessment. We show that using the spatiotemporal index in the assessment model greatly alters the estimates of recruitment and spawning stock biomass and the determination of stock status. Also, incorporating the spatiotemporal index leads to less retrospective bias and outperforms the model with design-based index in terms of predictive performance through a retrospective cross-validation test. Our results suggest that temporal variability of population abundance could be exaggerated by the design-based estimator, and such imprecision may greatly affect the performance of a stock assessment and subsequent development of management decisions.

种群相对丰度的估算趋势是鱼类种群评估的核心输入项。准确且精确的丰度估算，对于鱼类资源的有效保护与科学管理至关重要。经科学设计的数据采集流程可确保相对丰度估算结果无偏，但基于抽样设计的估算器在特定场景下的统计效率可能偏低。本研究采用新近开发的、纳入生境变量的时空模型，对缅因湾内北方长额虾（*Pandalus borealis*）的基于模型的丰度指数进行估算。本研究将该时空丰度指数与经典的基于抽样设计的丰度指数进行对比，并评估两种指数的差异对种群评估的影响。研究结果表明，在评估模型中使用时空丰度指数，会显著改变种群补充量与产卵群体生物量的估算结果，以及种群现状的判定。此外，通过回顾性交叉验证测试可知，纳入时空丰度指数可降低回顾偏差，且在预测性能上优于基于抽样设计的估算模型。本研究结果显示，基于抽样设计的估算器可能会夸大种群丰度的时间变异特征，而这种不精确性会显著影响种群评估的效果，以及后续管理决策的制定。