Movement patterns and search behaviour of a predatory marine fish

Marine environments are known for their dynamic, unpredictable nature. Therefore, search behaviour is particularly important for marine animals. Despite this, movement patterns and search behaviour of marine animals, and particularly fish, are poorly known. Here I investigate some unanswered questions relating to the search behaviour of a predatory marine fish, the small-spotted catshark (Scyliorhinus canicula). This research uses a combination of field-based tracking and laboratory investigations to evaluate the development of search behaviour. In the wild both male and female adults exhibited movements resembling central place foraging. These movements were characterised by preferential use of core areas from which discrete excursions were made at particular times prior to return to the core area. Despite this, sex differences in movements were found. Females undertook relatively infrequent, mainly nocturnal, long range excursions whereas males made more frequent excursions of variable duration and extent throughout both the day and night. In the laboratory, movement patterns of juveniles were consistent with a simple random walk model of movement, regardless of prey distribution or density. The resulting foraging efficiencies were also similar irrespective of treatment. The movements of males in the wild also appeared to be consistent with a random walk model, although a truncated-power law was found to be a good fit to some of the step length data, with exponent (μ) values indicative of optimal Lévy-like behaviour. Behaviour switching between different movement patterns in relation to complex changes in prey availability and distribution appears likely. In contrast, the movements of adult females in the field showed some degree of determinism, resulting in poor agreement with random walk models. The results of learning experiments with juveniles in the laboratory suggest that small-spotted catsharks may be capable of developing spatial memory, and such learning may be important for the development of efficient search tactics. Given these findings, the importance of learning with regards to search behaviour in catsharks warrants further investigation.