Data from: Sex-specific and individual preferences for hunting strategies in white sharks

Fine-scale predator movements may be driven by many factors including sex, habitat, and distribution of resources. There may also be individual preferences for certain movement strategies within a population which can be hard to quantify. Within top predators, movements are also going to be directly related to the mode of hunting; for example sit-and-wait or actively searching for prey. Although there is mounting evidence that different hunting modes can cause opposing trophic cascades, there has been little focus on the modes used by top predators, especially those in the marine environment. Adult white sharks (Carcharhodon carcharias) are well known to forage on marine mammal prey, particularly pinnipeds. Sharks primarily ambush pinnipeds on the surface but there has been less focus on the strategies they use to encounter prey. We applied mixed hidden Markov models to acoustic tracking data of white sharks in a coastal aggregation area in order to quantify changing movement states (Area Restricted Searching (ARS) vs. patrolling) and the factors that influenced them. Individuals were re-tracked over multiple days throughout a month to see if state-switching dynamics varied or if individuals preferred certain movement strategies. Sharks were more likely to use ARS movements in the morning and during periods of chumming by ecotourism operators. Furthermore, the proportion of time individuals spent in the two different states and the state-switching frequency, differed between the sexes and between individuals. Predation attempts/success on pinnipeds were observed for sharks in both ARS and patrolling movement states and within all random effects groupings. Therefore white sharks can use both a ‘sit-and-wait’ (ARS) and ‘active searching’ (patrolling) movements to ambush pinniped prey on the surface. White sharks demonstrate individual preferences for fine scale movement patterns which may be related to their use of different hunting modes. Marine top predators are generally assumed to use only one type of hunting mode, but we show that there is likely a mix within populations. As such, individual variability should be considered when modelling behavioural effects of predators on prey species.

精细尺度下的捕食者移动行为可能受多种因素驱动，包括性别、栖息环境以及资源分布。种群内部个体对特定移动策略也可能存在偏好，这类偏好往往难以量化。在顶级捕食者（top predators）中，移动行为还与捕猎模式直接相关，例如“静候伏击”（sit-and-wait）或是主动搜寻猎物。尽管已有越来越多的研究表明，不同的捕猎模式会引发截然相反的营养级联效应，但学界对顶级捕食者所采用的捕猎模式却鲜有关注，海洋环境中的顶级捕食者更是如此。成年大白鲨（Carcharhodon carcharias）以海洋哺乳动物为食，尤以鳍足类（pinnipeds）为主，这已是学界共识。大白鲨主要在海面伏击鳍足类猎物，但学界对其搜寻猎物所采用的策略却关注不足。本研究将混合隐马尔可夫模型应用于某海岸聚集区大白鲨的声学追踪数据，以量化其移动状态的动态变化——即区域限制搜索（Area Restricted Searching，ARS）与巡逻移动——以及影响这些状态的相关因素。研究人员在为期一个月的周期内对多只个体进行了多日连续追踪，以探究状态转换动态是否存在差异，或是个体是否存在特定的移动策略偏好。大白鲨在清晨时段以及生态旅游运营商进行投饵诱鲨的时段，更倾向于采用区域限制搜索模式。此外，个体在两种移动状态下的时间占比以及状态转换频率，均存在性别间与个体间的差异。研究观察到，无论是处于区域限制搜索还是巡逻移动状态的大白鲨，在所有随机效应分组中均存在对鳍足类的捕猎尝试或捕猎成功案例。由此可见，大白鲨可同时采用“静候伏击”（对应区域限制搜索模式）与“主动搜寻”（对应巡逻模式）两种移动策略，在海面伏击鳍足类猎物。大白鲨个体在精细尺度的移动模式上存在偏好，这可能与其所采用的不同捕猎模式相关。学界通常认为海洋顶级捕食者仅采用单一捕猎模式，但本研究表明，种群内部很可能同时存在多种捕猎模式。因此，在构建捕食者对猎物种群的行为影响模型时，应当纳入个体变异性这一因素。