Sex‐specific and individual preferences for hunting strategies in white sharks

Abstract

Summary 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 whether 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 may be a mix within populations. As such, individual variability should be considered when modelling behavioural effects of predators on prey species.

moveHMM: an R package for the statistical modelling of animal movement data using hidden Markov models

“…For example, in Towner et al . (), the decoded behavioural states of white sharks were superimposed on their movement tracks, which clearly highlighted spatial variation in the animals’ behavioural patterns. Similarly, Lidgard et al .…”

“…) and white sharks (Towner et al . ). Notably, the mean turning angle in state 2 was estimated as −0·299 – with 95% confidence interval [−0·312, −0·287], obtained using CI(m4) – hence confirming the tendency of the haggises to circle clockwise (when active).…”

Physiological stress responses to natural variation in predation risk: evidence from white sharks and seals

“…, Towner et al. ). However, among the different colonies targeted by sharks, predation risk to seals can vary significantly due to landscape features that either offer protection to seals traversing the gauntlet or leave them exposed to unpredictable risk of attack (Wcisel et al.…”

Shifting individual habitat specialization of a successful predator living in anthropogenic landscapes

“…Individual specialization is known to be widespread across a diverse set of taxa (Bolnick et al 2003, Bell et al 2009, Ceia & Ramos 2015, including different seabird species and other marine predators (e.g. Vander Zanden et al 2010, Votier et al 2010, Masello et al 2013, Ceia & Ramos 2015, Tyson et al 2015, Towner et al 2016, Yurkowski et al 2016. In general, individual specialization may have a strong impact on ecological processes and population dynamics, and there is evidence that this mechanism may reduce intra-specific competition among individuals, increase individual foraging efficiency and improve breeding success (Pierotti & Annett 1991, Bolnick et al 2003, Woo et al 2008, Araújo et al 2011.…”