Oral Presentation Australian Society of Fish Biology and Oceania Chondrichthyan Society Conference 2016

How do Port Jackson sharks find their home? (#113)

Catarina Vila Pouca 1 , Culum Brown 1
  1. Biological Sciences, Macquarie University, Sydney, NSW, Australia

Benthic shark species have long been understudied, especially concerning their movement ecology. While it was generally assumed they have small scale movements and limited ranges, recent studies have rendered this idea erroneous. In eastern Australia, Port Jackson sharks undertake seasonal migrations of hundreds of kilometres in a few weeks, and aggregate yearly in shallow rocky reefs off the NSW coast during the austral winter–spring season to breed. Interestingly, in the Jervis Bay Marine Park, NSW, both males and females have small home ranges and show over 90% site fidelity during the breeding season and from year to year. To better understand their fine scale movements and homing abilities, we displaced eight Port Jackson sharks 3-7 km from their home reef in Jervis Bay and used active acoustic telemetry to track their movements following release. Some sharks were displaced to different reefs in the bay, while others were released in deep sandy areas in the middle of the bay, and displacements were done in the morning or at dusk. Tagged sharks alternated between stationary and travelling states upon release, with most activity observed after sunset. Most sharks stopped moving once they reached a rocky area, but all returned to their capture location, even those released on reefs with habitat very similar to their home reef. This is the first study to experimentally test a benthic shark species’ ability to return home, and our preliminary results show Port Jackson sharks did not have a preferred compass bearing towards their home reef during the initial hours after displacement. This finding suggests they might not have a cognitive map of the whole bay and need to reach a familiar area to orient and navigate home.