Characteristics of spiny lobster, Jasus edwardsii, aggregations in exposed reef and sandy areas

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 ratio of aggregating lobsters varied considerably between seasons. Seasonal peaks in the proportion of male lobsters within the aggregations coincided with peak feeding rates in captive males. The presence of females was not as clearly related to their feeding patterns and probably also reflected behavioural adaptations associated with the carrying of eggs and release of larvae.