Abstract Fisheries are managed through various means to regulate harvest and maintain the sustainability of the stock. These regulations also influence which size fishes are removed from the population: A minimum mesh or hook size directly affects the size of fish retained by the fishing gear. A minimum fish size leads to discards, and any survival of released fish decreases the selectivity for sub-legal size classes. Closed areas and seasons indirectly influence size selectivity by altering the relative availability of each size class. Collectively, these regulations control the population-level size selectivity of the fishery, which is the product of gear selection (modulated by discard mortality) and spatiotemporal availability. Stock assessment models are particularly vulnerable to incorrectly specified selectivity, yet it is difficult to independently validate the structure of this variable because it is influenced by several processes. We analyzed the Gulf of Maine fishery for Atlantic cod (Gadus morhua), which has been intensively regulated through a complex management system for several decades, and deconstruct the mechanisms through which regulations have influenced fishery selectivity. Gear selection-at-size was estimated for four fleets under two regulatory regimes by comparing the size distribution of survey and fishery catches, sampled from the same time and area. Availability-at-size was estimated by weighting predictions from a random forest model of fish density-at-size by the spatiotemporal pattern of fishing effort. Several regulations caused fishery selectivity to be distinctly dome-shaped, and regulatory changes altered the shape of this curve over time. The approach of deconstructing selectivity into its gear and availability components can be adapted to other stocks to elucidate the underlying mechanisms, inform assessment models, and evaluate alternate regulation scenarios.

中文翻译：

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解构尺寸选择性以评估渔业管理的影响

摘要 渔业通过各种方式进行管理，以调节收获并保持种群的可持续性。这些规定还影响从种群中移除的鱼的大小：最小网眼或钩子的大小直接影响渔具保留的鱼的大小。鱼的最小尺寸会导致丢弃，而释放鱼的任何存活都会降低对低于法定尺寸等级的选择性。封闭区域和季节通过改变每个尺寸等级的相对可用性间接影响尺寸选择性。总的来说，这些法规控制着渔业的种群规模选择性，这是渔具选择（由丢弃死亡率调节）和时空可用性的产物。库存评估模型特别容易受到错误指定的选择性的影响，然而，很难独立验证这个变量的结构，因为它受多个过程的影响。我们分析了缅因湾渔业的大西洋鳕鱼 (Gadus morhua)，几十年来一直通过复杂的管理系统对其进行严格监管，并解构了监管影响渔业选择性的机制。通过比较来自同一时间和区域的调查和渔业捕捞量的大小分布，估计了两种监管制度下四个船队的按规格选择的网具。规模可用度是通过渔业努力的时空模式对鱼类密度随机森林模型的加权预测来估计的。一些法规导致渔业选择性明显呈圆顶状，随着时间的推移，监管变化改变了这条曲线的形状。将选择性解构为齿轮和可用性组件的方法可适用于其他种群，以阐明潜在机制、为评估模型提供信息并评估替代监管方案。