Environmental change and anthropogenic activity, alone or in combination, may cause vital rates of fish populations to exhibit low-frequency, large-magnitude variation leading to non-stationary population processes in inherently dynamic ecosystems. It remains unclear why, when and, so, whether, non-stationary population processes should be taken into account in fisheries stock assessment models. Here, we clarify the necessity and conditions for including non-stationary population processes in stock assessment models. Specifically, the convention of treating population vital rates with constant parameters might be unreliable under regime shifts characterized by low-frequency, large-magnitude variation in drivers of fish population dynamics. We hypothesized and simulated effects of a U-shaped trade-off between the length of time-series data and model estimation error for fish populations exhibiting non-stationary dynamics. In the case of low-frequency, large-magnitude variation, when measurement errors were small, the effects of non-stationary population processes were stronger than otherwise. Including time-varying parameters of population vital rates in the assessment model resolved this dilemma as anticipated, albeit at the cost of increased model complexity, suggesting that accounting for non-stationarity with time-varying parameters alone may not be sufficient to improve stock assessments and other approaches should also be considered.

中文翻译：

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越长越好吗？动态生态系统中渔业资源评估的权衡

环境变化和人为活动，单独或结合，可能导致鱼类种群的生命率表现出低频、大范围的变化，从而导致固有动态生态系统中的非平稳种群过程。目前尚不清楚为什么、何时以及是否应在渔业资源评估模型中考虑非平稳种群过程。在这里，我们阐明了在种群评估模型中包含非平稳种群过程的必要性和条件。具体来说，在以鱼类种群动态驱动因素的低频、大幅度变化为特征的政权转移下，用恒定参数处理种群生命率的惯例可能不可靠。我们假设并模拟了时间序列数据长度与模型估计误差之间的 U 形权衡效果，以展示非平稳动态的鱼类种群。在低频、大幅度变化的情况下，当测量误差较小时，非平稳种群过程的影响强于其他情况。在评估模型中包括人口生命率的时变参数按预期解决了这一困境，尽管以增加模型复杂性为代价，这表明仅考虑时变参数的非平稳性可能不足以改善种群评估和还应考虑其他方法。当测量误差较小时，非平稳种群过程的影响强于其他情况。在评估模型中包括人口生命率的时变参数按预期解决了这一困境，尽管以增加模型复杂性为代价，这表明仅考虑时变参数的非平稳性可能不足以改善种群评估和还应考虑其他方法。当测量误差较小时，非平稳种群过程的影响强于其他情况。在评估模型中包括人口生命率的时变参数按预期解决了这一困境，尽管以增加模型复杂性为代价，这表明仅考虑时变参数的非平稳性可能不足以改善种群评估和还应考虑其他方法。