School of Mathematics and Physics, The University of Queensland, Australia.
Department of Mathematics, University of Pittsburgh, PA, United States.
Math Biosci. 2024 Jan;367:109111. doi: 10.1016/j.mbs.2023.109111. Epub 2023 Nov 22.
In many countries, sustainability targets for managed fisheries are often expressed in terms of a fixed percentage of the carrying capacity. Despite the appeal of such a simple quantitative target, an unintended consequence may be a significant tilting of the proportions of biomass across different ages, from what they would have been under harvest-free conditions. Within the framework of a widely used age-structured model, we propose a novel quantitative definition of "age-balanced harvest" that considers the age-class composition relative to that of the unfished population. We show that achieving a perfectly age-balanced policy is impossible if we harvest any fish whatsoever. However, every non-trivial harvest policy has a special structure that favours the young. To quantify the degree of age-imbalance, we propose a cross-entropy function. We formulate an optimisation problem that aims to attain an "age-balanced steady state", subject to adequate yield. We demonstrate that near balanced harvest policies are achievable by sacrificing a small amount of yield. These findings have important implications for sustainable fisheries management by providing insights into trade-offs and harvest policy recommendations.
在许多国家，管理渔业的可持续性目标通常以承载能力的固定百分比来表示。尽管这样一个简单的定量目标很有吸引力，但一个意想不到的后果可能是生物量在不同年龄的比例发生显著倾斜，与在无捕捞条件下的比例相比。在一个广泛使用的年龄结构模型框架内，我们提出了一种新的“年龄平衡捕捞”的定量定义，该定义考虑了相对于未捕捞种群的年龄组成。我们表明，如果我们捕捞任何鱼类，那么实现完全年龄平衡的政策是不可能的。然而，每一个非平凡的捕捞政策都有一个特殊的结构，有利于年轻人。为了量化年龄失衡的程度，我们提出了一个交叉熵函数。我们制定了一个优化问题，旨在在适当的产量下达到“年龄平衡的稳定状态”。我们证明，通过牺牲少量产量，可以实现接近平衡的捕捞政策。这些发现对可持续渔业管理具有重要意义，为权衡和捕捞政策建议提供了见解。
