Spatial scales of benthic invertebrate habitats from fishery by catch and video transect data in the Ross Sea region

High resolution VME taxa bycatch data (at the longline segment level) has been collected for two fishing seasons, with 4728 longline segments observed. Several regions with consistent presence of sponge and/or gorgonian bycatch are identifiable, as are several areas of dense fishing effort with no evidence of sponge or gorgonian presence. Identifiable sponge and/or gorgonian habitats occurred at a typical scale of 10-30 km², though some sponge habitats appeared larger. Spatial analysis of these data allows the detectability of sponges and gorgonian corals to be estimated, along with changes in catch rate at different densities. Results indicate that sponge patches are detected more than 70% of the time when present, and gorgonian patches are detected more than 60% of the time. Video transects on the Ross Sea slope from New Zealand’s 2008 IPY voyage provided data on the fine scale distributions (i.e. < 600 m) of sponges, stony corals, and ascidians. The prevalence of sponge and gorgonian habitats also varies among four benthic bioregions developed for the Ross Sea. Together, the data show that sponges and other vulnerable taxa occur in complex mosaic patterns of small patches dispersed within larger habitats. Confirmation of these results is necessary using independent methods such as underwater video and would provide a method to link bycatch observations to habitat density on the seafloor.