Risky business: consistent breeding migration in a benthic shark despite environmental variability

The timing of migration is essential for the survival and reproductive success of migratory species. Environmental and biological factors can influence the breeding success of these migrations. However, there is a lack of long-term studies on benthic migratory species that analyse their response to climatic variation. Climate change may threaten the breeding migration of species that rely on environmental cues to initiate migration. Port Jackson sharks, Heterodontus portusjacksoni, display high philopatry to their breeding grounds. Using passive acoustic telemetry, this study investigated the annual migration patterns of Port Jackson sharks at a breeding aggregation site in Jervis Bay, Australia. The influence of biological (sex and size) and environmental factors (temperature, East Australian current strength, rainfall, moon phase and period of the day) on these patterns was assessed over a 7-year period (2013–2019). The results of the linear mixed-effects models revealed annual and individual variability in migration timing, with males arriving and departing earlier than females. There was no influence of environmental variables on the migration timing of Port Jackson sharks. We found that more sharks arrived and departed at night. Overall, there was significant repeatability in migration timing for both arrival and departure. This interannual individual consistency has important implications for breeding success at the population level. Migration patterns that are unresponsive to environmental cues may lead to a mismatch between migration timing and suitable conditions for juvenile survival.