Autonomous large scale urchin barren mapping with interferometric sonar

The southern expansion of long spined urchin (Centrostephanous rodgersii) into Tasmanian waters will have a negative impact on the two biggest wild fisheries through the creation of urchin barrens. The rock lobster and abalone fisheries were valued at $163 million to the state of Tasmania in 2012 and accounted for 96% of all wild caught production by value (Skirtun, Sahlqvist, Vieira, (2013)). A key to future management of the spread and impact of Centrostephanus rodgersii is the ability to produce large scale, semi-automated maps showing current distribution of urchin barrens. The aim of this research is to investigate the application of using interferometric sonar mounted on an Autonomous Underwater Vehicle (AUV) as a method for urchin barren mapping. On the east coast of Tasmania, Phyllospora comosa and Ecklonia radiata are the most common alga in the depth range predominantly affected by urchins. Both these species form dense canopies up to 2m above the seabed. It is hypothesized in this work that the algal canopy will affect the uncertainty in the bathymetric model generated from interferometric sonar and that this uncertainty can then be used to map potential barren sites.