We present an age-structured multi-fleet model with cannibalism mortality and endogenous weight at age. Using the model and three simplified versions, we show that assumptions of exogenous natural mortality and weight can lead to significant underestimation of optimal fishing mortality in both maximum sustainable yield (MSY) and maximum economic yield (MEY) scenarios for long-lived cannibalistic fish such as the Northeast Arctic cod. In addition, we show that the harvest, spawning stock biomass (SSB), and net present value (NPV) levels associated with optimal exploitation rates increase significantly with assumptions of exogenous natural mortality and weight. The underestimation of optimal fishing mortality, and the corresponding overestimation of SSB and NPV, is more significant in MSY than MEY scenarios. Meanwhile, the overestimation of harvest is more significant in MEY than MSY scenarios. The study also confirms that the Northeast Arctic cod fishery can achieve higher sustainable yield and NPV by changing the fleet composition and target reference points.

中文翻译：

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生物经济模型中的内源性与外源性自然死亡率和权重

我们提出了一个年龄结构的多舰队模型，具有自相残杀死亡率和年龄内源性体重。使用该模型和三个简化版本，我们表明，外源自然死亡率和体重的假设可能导致在最大可持续产量（MSY）和最大经济产量（MEY）情景中对长寿命同类相食鱼类的最佳捕捞死亡率的严重低估，例如作为东北北极鳕鱼。此外，我们表明与最佳开采率相关的收获、产卵种群生物量 (SSB) 和净现值 (NPV) 水平随着外生自然死亡率和体重的假设而显着增加。对最佳捕捞死亡率的低估，以及对 SSB 和 NPV 的相应高估，在 MSY 情景中比 MEY 情景更为显着。同时，在 MEY 中，高估收成比在 MSY 情景中更为显着。该研究还证实，北极东北部鳕鱼渔业可以通过改变船队组成和目标参考点来实现更高的可持续产量和 NPV。