Use of High-Resolution Sonar to Quantify Attributes of Predation on Reef Fishes at Ecologically Relevant Time and Space Scales

Predator-prey interactions are difficult to study in the ocean due to limitations in the space and time requirements for observations.  Small-scale direct underwater observations by divers (<10m²) and large-scale hydroacoustic surveys (100s - 1000s m²) are traditional approaches.  However, large piscivorous predators identify and attack prey at the scale of tens of meters. Dual-Frequency Identification Sonar, or DIDSON, is a high-resolution acoustic camera operating in the MHz range that provides detailed continuous imaging of objects out to 30 m range. Observations using DIDSON can provide an intermediate spatial scale viewpoint at specific sites by providing a larger picture over long periods of time. The fine-scale aspects of predation (such as predator and prey group size, predation rates, use of landscape features by both predator and prey, etc) and indirect predator interactions (e.g, the driving of prey to the bottom by midwater predators where they are then fed on by demersal predators) are critical to understanding the reef community structure as a whole. This greater understanding can aid in developing more comprehensive management strategies.  Preliminary group size and predator landscape use data was collected in 2009 in Gray’s Reef National Marine Sanctuary off the coast of Georgia; a return trip is planned for 2011 to expand on these findings. Here I assess the utility of DIDSON for observing predation in reef communities to close the gap between traditional small and large scale observation methods.