Total allowable catch restrictions (hereafter referred to as catch quotas) play an important role in maintaining healthy fish stocks. While studies have identified a positive relationship between catch quota implementation and improved stock status, these methods are subject to selection bias as catch quotas are typically applied to stocks that are depleted. We address this challenge using the synthetic control method, which estimates the causal effect of catch quotas on fishing mortality and biomass by predicting a synthetic counterfactual outcome. We focus on high seas stocks (tunas, billfishes, and sharks) managed by tuna Regional Fisheries Management Organizations (tRFMOs), first providing an overview of stock status and current management measures in place. We find that implementation of catch quotas by tRFMOs has more than doubled over the past decade. Second, we predict the hypothetical fishing mortality and biomass trajectory for seven high seas quota-managed stocks in absence of a catch quota. These “synthetic non-quota stocks” are predicted using a weighted selection of high seas non-quota stocks. Credibility of the synthetic non-quota stocks is evaluated through diagnostic checks, and robustness tests assess sensitivity to study design. Five credible fishing mortality synthetic controls are predicted: three add support to the hypothesis that catch quotas successfully reduce fishing mortality, while two find that catch quotas increase fishing mortality. While our analysis is limited in scope, given that all seven quota-managed stocks are managed under a single tRFMO, we highlight the potential for the synthetic control method in fisheries management evaluation.

中文翻译：

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一种估计公海总允许捕捞量影响的综合控制方法

总允许捕捞限制（以下称为捕捞配额）在维持健康的鱼类种群方面发挥着重要作用。虽然研究已经确定捕捞配额实施与改善种群状况之间存在正相关关系，但这些方法存在选择偏差，因为捕捞配额通常适用于枯竭的种群。我们使用综合控制方法应对这一挑战，该方法通过预测综合反事实结果来估计捕捞配额对捕捞死亡率和生物量的因果影响。我们关注由金枪鱼区域渔业管理组织 (tRFMO) 管理的公海种群（金枪鱼、长嘴鱼和鲨鱼），首先概述种群状况和当前的管理措施。我们发现，在过去十年中，tRFMO 实施的捕捞配额增加了一倍以上。其次，我们预测了在没有捕捞配额的情况下七种公海配额管理的种群的假设捕捞死亡率和生物量轨迹。这些“合成非配额库存”是使用公海非配额库存的加权选择来预测的。合成非配额库存的可信度通过诊断检查进行评估，稳健性测试评估对研究设计的敏感性。预测了五种可靠的捕捞死亡率综合控制：三种增加了对捕捞配额成功降低捕捞死亡率的假设的支持，而两种发现捕捞配额增加了捕捞死亡率。虽然我们的分析范围有限，但鉴于所有七种配额管理的种群都由一个 tRFMO 管理，