Use of high-resolution acoustic cameras to study reef shark behavioral ecology

Abstract

Shark species play an important role in shaping marine communities, ecosystems, and community assemblages, yet their high mobility and low abundances in certain locations makes studying the way they interact with these systems difficult. Here high-resolution acoustic cameras are demonstrated as effective tools to study the ecology and behavior of reef and coastal sharks that operate in the vicinity of a near-pristine coral reef atoll. The acoustic camera generated detailed imagery and size measurements from >1000 sightings of sharks that traversed a discrete corridor linking two of the atoll's distinct marine habitats, the forereef and offshore pelagic habitat with the atoll's lagoon. Daily shark density and estimated biomass values varied considerably through time, but generally approximated values calculated using less comprehensive and more labor-intensive techniques at this same atoll. Diel patterns in shark movements revealed elevated shark presence during low-light periods of the day (e.g. peak sighting density just after dusk), but weaker links between shark movement patterns and tides. Data gathered through use of this tool extends and reinforces some of the observations made of smaller numbers of sharks using traditional data collection methods while providing unique additional insights into the ways that larger numbers of sharks operate at fine spatial scales over longer periods of time. Behavioral information of this type is critical to developing effective management plans for these vulnerable species.