A large portion of the catch in many stocks may comprise discards which need to be accounted for in assessments in order to avoid bias in estimates of fishing mortality, stock biomass and reference points. In age structured assessment models, discards are sometimes treated as a separate fleet or are added to the landings before fitting so that information about discard behavior and sampling error is lost. In this paper an assessment model is developed to describe the discard process with size as a covariate while retaining age structured population dynamics. Discard size selection, high grading and bulk dumping of fish at sea are modelled so that the temporal dynamics of the process can be quantified within the assessment. The model is used to show that discarding practices have changed over time in a range of Northeast Atlantic demersal fish. In some stocks there is a substantial increase in high grading and evidence for bulk discarding which can be related to regulatory measures. The model offers a means of identifying transient effects in the discard process that should be removed from both short-term forecasts and equilibrium reference point calculations

中文翻译：

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将丢弃物纳入种群评估模型

许多种群的大部分渔获量可能包括丢弃物，在评估中需要考虑这些丢弃物，以避免对捕捞死亡率、种群生物量和参考点的估计产生偏差。在年龄结构化评估模型中，丢弃物有时被视为一个单独的船队，或者在拟合之前被添加到上岸量中，从而丢失了关于丢弃行为和采样错误的信息。在本文中，开发了一个评估模型来描述以大小为协变量的丢弃过程，同时保留年龄结构的人口动态。对丢弃大小的选择、高等级和海上鱼类的大量倾倒进行建模，以便可以在评估中量化该过程的时间动态。该模型用于显示一系列东北大西洋底栖鱼类的丢弃做法随着时间的推移而发生变化。在一些种群中，可能与监管措施有关的高等级和大量丢弃的证据显着增加。该模型提供了一种识别丢弃过程中应从短期预测和平衡参考点计算中去除的瞬态影响的方法