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    Further analysis of spatial patterns of benthic invertebrate habitats from fishery bycatch in the Ross Sea region

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    S.J. Parker, R.G. Cole and S.M. Hanchet (New Zealand)

    High resolution VME taxa bycatch data (at the longline segment level) have been collected for two fishing seasons, with 4 728 longline segments observed. Several regions with consistent presence of VME taxa bycatch are identifiable, as are several areas of dense fishing effort with no evidence of VME taxa. Identifiable sponge and/or gorgonian habitats occurred at a typical scale of 10-30 km2, though some sponge habitats may have been larger. Other taxa were not clustered at small scales, but were at larger scales. Spatial analysis of these data allows the detectability of prevalent taxa to be estimated, along with changes in catch rate at different levels of observed bycatch. Results indicate that several VME taxa are detected between 60% and 80% of the time when present, and that probability of detection was higher near areas with other high bycatch observations. Video transects on the Ross Sea slope from New Zealand’s 2008 IPY voyage were used to characterise the fine scale distributions (i.e. < 600 m) of sponges, stony corals, and ascidians. The prevalence of six VME taxa also varies among four benthic bioregions developed for the Ross Sea. Together, the data show that 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.