Evidence for personality in the field

As already described in chapter 1, evidence for personality in the wild was demonstrated in the Port Jackson sharks (Byrnes et al., 2016b). I would like to repeat that this study is applicable to numerous species, including bottom dwelling sharks, such as nurse sharks or catsharks providing an interesting guideline for future studies. However, it remains unclear how this could be adapted to larger animals or relate to naturally occurring behaviors. It will be also important to develop less intrusive methods.

5.4.1.a The juvenile bull shark as a model species for personality research

Investigations of juvenile bull sharks (Carcharhinus leucas) were successfully used to detect consistent individual differences in behavior (Matich & Heithaus, 2015), revealing their study system as particularly promising for the study of personality in sharks. Prior to discussing this study, it is interesting to note parallels with the juvenile lemon shark studies described above.

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Like lemon sharks, which use mangrove fringed habitats as nursery areas, juvenile bull sharks can also be found using estuarine or freshwater habitats. Some of these habitats are known to be safer (less predation) but less productive (less food) further upstream (further away from the marine environment) (Matich & Heithaus, 2015), and so are comparable to what is experienced by juvenile lemon sharks in Bimini. These similarities suggest that juvenile bull sharks face similar trade-offs between benefits and risks, which could promote individual differences. Indeed, Matich et al. (2011) found that individual juvenile bull sharks from their study site differed in their diet. Some individuals fed in the riskier marine food web and others in the safer estuarine habitat, which led the authors to propose that individuals differed in their risk-benefit strategies. More recently, in the same system, juvenile bull sharks were found to differ in their movements and in the portion of the estuary they used, with some being detected more often in riskier locations (e.g., downstream near the mouth) than others (Matich

& Heithaus, 2015). These consistent individual differences were documented for at least four months and were independent of age class. Unfortunately, these investigations were performed on different groups of individuals leaving the existence of a potential relationship between individual differences in estuary use and feeding habit unproven.

It is important to note that estuarine systems can be heterogeneous and so, until there is evidence for personality in a more controlled environment, it is challenging to disentangle what could be related to responses to environmental conditions or to individual behavioral differences. For instance, Ortega et al., (2009) investigated movement in juvenile bull sharks in Florida and in another river system. Similarly, they found differences in movement between two groups of juvenile bull sharks but explained that these could have been related to the locations within the river and the differences in habitat within these areas. Regardless, juvenile bull sharks are a promising model with which to investigate consistent individual differences in behavior. The heterogeneity of predator pressure and resource abundance in the

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juvenile bull sharks’ nursery habitat contributes to the likelihood that personality differences are present in this species. Longer term studies along with a demonstration of a long-lasting relationship between movement differences and feeding location differences (risky marine web food versus safer estuary) or life history traits (e.g., growth rate and survival) would strongly suggest that these differences reflect (at least partly) consistent individual differences and demonstrate the ecological importance of such differences. In the best scenario, individual differences should be investigated in controlled captive or semi-captive conditions and then in the field (e.g., Herborn et al., 2010; Yuen et al., 2016). This strategy would, for instance, allow researchers to further investigate if habitat use variability is due to differences in boldness, dominance, sociability, or exploration.

5.4.1.b Behavioral assays in large free ranging sharks

Being usually shy, wide ranging and aquatic animals, sharks behavior is difficult to observe in many species. The need to score the same individuals multiple times, to demonstrate personality, logically further amplifies this difficulty. However, as shark personality receives more attention, systems and methods are likely to be identified and developed.

For instance, white sharks provide a potential model to study personality in a large, upper-trophic predator. White sharks can be attracted to research boats using bait and repeatedly observed over months or years, as demonstrated by the development of eco-tourism in South Africa (e.g., Laroche et al., 2007). This opens up the possibility to observe the same individual multiple times. Furthermore, these sharks have been observed inspecting novel objects on the water surface (Hammerschlag et al., 2012). These characteristics were taken advantage of by William Hughes, Marlene Stürup and colleagues in their investigation of individual differences in the behavior of white sharks, and the preliminary results are encouraging (William Hughes, personal communication). If these tests are applicable to personality research, they might provide a method for testing personality in large sharks in the

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wild. These methods could be used to further investigate the relationships between personality traits (such as novel object inspection) and individual differences in observed behaviors, such as movements, space use, hunting strategy, social interactions, feeding habits, and more, to be described below.

The examples given above in addition to lemon sharks and catsharks (see introduction) provide a solid ground for future investigations aiming at investigating the transferability of personality into the wild and consistent individual differences in natural behavior. Indeed, combined together they provide different methods to test personality in captivity and in the wild. Therefore, crossing methodologies will provide a strong step forward into the study of personality in wild sharks. Considering the growing evidence for inter-individual variability in their natural behavior across several species with diverse taxonomy, biology, and behavior, such effort is of critical importance. In order to argue this point, the following paragraphs will discuss such studies.

5.4.2 Evidence for inter-individual variation in shark behavior: reasons to study shark