Sexual Segregation in Juvenile New Zealand Sea Lion Foraging Ranges: Implications for Intraspecific Competition, Population Dynamics and Conservation

Sexual segregation (sex differences in spatial organisation and resource use) is observed in a large range of taxa. Investigating causes for sexual segregation is vital for understanding population dynamics and has important conservation implications, as sex differences in foraging ecology may affect vulnerability to area-specific human activities. Although behavioural ecologists have proposed numerous hypotheses for this phenomenon, the underlying causes of sexual segregation are poorly understood. We examined the size-dimorphism and niche divergence hypotheses as potential explanations for sexual segregation in the New Zealand (NZ) sea lion (Phocarctos hookeri), a nationally critical, declining species impacted by trawl fisheries. We used satellite telemetry and linear mixed effects models to investigate sex differences in the foraging ranges of juvenile NZ sea lions. Male trip distances and durations were almost twice as long as female trips, with males foraging over the Auckland Island shelf and in further locations than females. Sex was the most important variable in trip distance, maximum distance travelled from study site, foraging cycle duration and percent time at sea whereas mass and age had small effects on these characteristics. Our findings support the predictions of the niche divergence hypothesis, which suggests that sexual segregation acts to decrease intraspecific resource competition. As a consequence of sexual segregation in foraging ranges, female foraging grounds had proportionally double the overlap with fisheries operations than males. This distribution exposes female juvenile NZ sea lions to a greater risk of resource competition and bycatch from fisheries than males, which can result in higher female mortality. Such sex-biased mortality could impact population dynamics, because female population decline can lead to decreased population fecundity. Thus, effective conservation and management strategies must take into account sex differences in foraging behaviour, as well as differential threat-risk to external impacts such as fisheries bycatch.性隔离（即空间分布模式与资源利用的性别差异）广泛存在于众多生物类群中。探究性隔离的成因，对于理解种群动态至关重要，同时具备重要的保护意义——因为觅食生态学中的性别差异，可能会影响物种对特定区域人类活动的易感性。尽管行为生态学家已针对该现象提出诸多假说，但性隔离的潜在成因仍未得到充分阐释。本研究以受拖网渔业影响的国家极危、种群衰退物种新西兰海狮（Phocarctos hookeri）为研究对象，验证了体型二态性假说与生态位分化假说作为其性隔离潜在解释的可行性。我们采用卫星遥测技术与线性混合效应模型，探究了幼年新西兰海狮觅食范围的性别差异。雄性海狮的行程距离与时长几乎为雌性的两倍，其觅食区域覆盖奥克兰群岛陆架且范围较雌性更为偏远。在行程距离、离研究样地的最大移动距离、觅食周期时长以及海上耗时占比等指标中，性别是影响最为显著的变量；而体重与年龄对这些特征的影响相对微弱。本研究结果支持生态位分化假说的预测，该假说认为性隔离能够降低种内资源竞争。由于觅食范围存在性隔离，雌性觅食栖息地与渔业作业区域的重叠比例近乎为雄性的两倍。这种分布模式使得幼年雌性新西兰海狮面临比雄性更高的资源竞争与渔业误捕风险，进而可能导致雌性死亡率更高。这种性别偏向性死亡会对种群动态产生影响，因为雌性种群数量下降会降低整体种群的繁殖力。因此，有效的保护与管理策略必须兼顾觅食行为的性别差异，以及渔业误捕等外部影响带来的差异化威胁风险。