Age-specific habitat preference, carrying capacity, and landscape structure determine the response of population spatial variability to fishing-driven age truncation

1. Understanding the mechanisms underlying spatial variability of exploited fish is critical for the sustainable management of fish stocks. Empirical studies suggest that size-selective fishing can elevate fish population spatial variability (i.e., more heterogeneous distribution) through age truncation, making the population less resilient to changing environment. However, species differ in how their spatial variability respond to age truncation and the underlying mechanisms remain unclear. 2. We hypothesize that age-specific habitat preference, together with environmental carrying capacity and landscape structure, determines the response of population spatial variability to fishing-induced age truncation. To test these hypotheses, we design an individual-based model of an age-structured fish population on a two-dimensional landscape under size-selective fishing. Individual fish reproduces and survives, and moves between habitats according to age-specific habitat preference and density-dependent habitat selection. 3. Population spatial variability elevates with increasing age truncation and the response is stronger for populations with stronger age-specific habitat preference. On a gradient landscape, reducing carrying capacity elevates the relative importance of density-dependence in habitat selection, which weakens the response of spatial variability to age truncation for populations with strong age-specific habitat preference. On a fragmented landscape, both populations with strong and weak age-specific habitat preferences are restricted at local optimal habitats, and reducing carrying capacity weakens the responses of spatial variability to age truncation for both populations. 4. Synthesis and applications. We demonstrate that to track and predict the changes in population spatial variability under exploitation, it is essential to consider the interactive effects of age-specific habitat preference, carrying capacity, and landscape structure. To improve spatial management in fisheries, it is crucial to enhance empirical and theoretical developments in the methodology to quantify age-specific habitat preference of marine fish, and to understand how climatic change influences carrying capacity and landscape continuity.

1. 探明被开发鱼类的空间变异内在机制，对鱼类种群资源（fish stocks）的可持续管理至关重要。实证研究表明，尺寸选择性捕捞（size-selective fishing）可通过年龄截断（age truncation）加剧鱼类种群的空间变异（即分布异质性提升），降低种群应对环境变化的恢复力。然而，不同物种的空间变异对年龄截断的响应存在差异，其背后的内在机制仍不明确。
2. 本研究提出假说：物种特异性生境偏好（age-specific habitat preference）、环境承载力（environmental carrying capacity）与景观结构（landscape structure）共同决定了种群空间变异对捕捞诱导的年龄截断的响应模式。为验证上述假说，我们在二维景观上构建了尺寸选择性捕捞下的年龄结构鱼类种群（age-structured fish population）的个体基模型（individual-based model）。模型中，个体鱼类依据物种特异性生境偏好与密度依赖的生境选择规则完成繁殖、存活，并在不同生境间移动。
3. 种群空间变异随年龄截断程度加深而升高，且物种特异性生境偏好越强的种群，其空间变异的响应幅度越大。在梯度景观中，降低环境承载力会提升生境选择中密度依赖效应的相对重要性，进而削弱强物种特异性生境偏好种群的空间变异对年龄截断的响应。在破碎化景观中，无论物种特异性生境偏好强弱，种群均会被限制在局域最优生境中，且降低环境承载力均会削弱两类种群的空间变异对年龄截断的响应。
4. 综合与应用。本研究证实，若要追踪并预测开发利用下种群空间变异的变化，必须考虑物种特异性生境偏好、环境承载力与景观结构的交互效应。为优化渔业空间管理，亟需推进海洋鱼类物种特异性生境偏好量化方法的实证与理论研究，并阐明气候变化如何影响环境承载力与景观连通性（landscape continuity）。