Intraspecific variation in diel patterns of rocky reef use suggests temporal partitioning in Port Jackson sharks

Limited information exists about the temporal residency patterns of marine predators, especially at the individual level. Temporal partitioning of resources can reduce intra-specific competition, but this has seldom been examined in predators in marine ecosystems. Here, we used 8 years of acoustic telemetry data from 27 receivers deployed in a large coastal embayment to examine the temporal residency of 51 Port Jackson sharks (Heterodontus portusjacksoni), during their breeding season. We found that the residency lengths of male and female Port Jackson sharks on breeding reefs differed throughout the breeding season, with males showing longer residency at the start of the season and females showing longer residency at the end of the season. Port Jackson sharks also showed a 24-h or diel periodicity in their detection patterns. Although the majority of individuals were nocturnal, a small proportion of sharks was detected more frequently during the day, possibly to reduce competition for resources. Surprisingly, there was no difference in the sex ratio nor the size of diurnal and nocturnal individuals. This study provides long-term insight into the temporal residency patterns of mesopredatory sharks at a breeding site and, more broadly, our results highlight the importance of studying temporal variation at the individual level in movement ecology studies.

Automated summary

Limited information exists about the temporal residency patterns of marine predators, especially at the individual level. Temporal partitioning of resources can reduce intra-specific competition, but this has seldom been examined in predators in marine ecosystems. The study found that male and female Port Jackson sharks exhibited different residency patterns during their breeding season and showed a 24-h diel periodicity in their detection patterns. While most individuals were nocturnal, a small proportion of sharks were more frequently detected during the day, possibly to reduce competition for resources.