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The behaviour and characteristics of J. edwardsii within offshore aggregations in northern New Zealand are described. Groups of up to 200 lobsters were found aggregating beyond the coastal reefs by day, on open sand, amongst beds of the emergent bivalve Atrina zelandica, and around low-lying patch reefs which had little topographical relief. Lobsters within the aggregations displayed behaviour consistent with the use of mutual defence. In areas of open sand, aggregations were circular, with individuals on the perimeter always facing outwards. These lobsters held their stout, spiny antennae upright and used them to fend off potential threats. On patch reefs and around Atrina beds, aggregations were less uniform in shape, and lobsters increased their level of physical protection by clustering against irregularities in the substratum. Offshore aggregations were found over 7 months of the year, but the size and sex …