To roam or to home: site fidelity in a tropical coastal shark

Understanding patterns in site fidelity is important for defining the ecological role of species in the systems they use and for gauging the effects of human impacts on their populations. We analyzed long-term movement data of adult spottail sharks (Carcharhinus sorrah) in Cleveland Bay, Australia, to define the degree of site fidelity this species shows to coastal areas. Individuals were monitored in the study site for 28-566 days, and residency index (i.e., proportion of days present to total monitoring period) ranged from 0.08 to 0.95. Using a randomization procedure, we determined that the movement paths for 90 % of individuals (11 female and 7 male) were more constrained than random, with individuals exhibiting a high degree of site fidelity to consistent areas within the study site. Examining distances moved revealed that individuals used the same areas repeatedly and remained in close proximity (i.e., < 6 km) to their location of first detection. While some individuals consistently used and returned back to the same locations, low residency among others suggests that a portion of the population may roam more widely. Long-term site fidelity to consistent areas may be a successful behavioral strategy for C. sorrah by increasing individual fitness through spatial familiarity and knowledge of resources.