Are sharks attracted to caged fish and associated infrastructure?

Abstract

There are increasing concerns over the possible effects of aquaculture pens on the local abundance and residency of sharks, and its associated risk for shark bites at nearby beaches and surf breaks. We used acoustic tracking and a before–during–after–control–impact design to assess the residency and local abundance of 117 bronze whalers and 843 white sharks around a 45-m-diameter aquaculture pen installed in South Australia for tourism purposes. Only 14 bronze whalers (12.0% of individuals tagged) and nine white sharks (1.1% of individuals tagged) were detected throughout the 5-year monitoring period and there was no evidence of the pen affecting these sharks, in either the number of sharks detected or number of detections (proxy for length of time detected). The low amount of interactions with the pen was likely to be due to a combination of low fish biomass, pen installed in a shallow location, local shark species being migratory species, and good husbandry practices. Adequate planning and management, and good husbandry practices, such as removal of dead fish from pens and avoiding over-feeding to ensure the feed is entirely consumed, are key to reducing shark interactions with cage fish and associated infrastructure.