Dusky dolphin nursery groups off Kaikoura, New Zealand



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The distribution, behaviours, and composition of dusky dolphin (Lagenorhynchus obscurus) nursery groups off Kaikoura, New Zealand, were examined. Data were collected during January?May 2005 and December 2005?April 2006 by systematic boat based surveys, group focal follows and photo-identification techniques. A total of 99 nursery groups were encountered on survey. Nursery groups were encountered in shallow water (<20 m) significantly more often than in deeper water (>20 m). Other group types (large groups, mating groups, adult non-mating groups) were not found in shallow water significantly more often than in deeper water. By staying in the shallower water, nursery groups may be protected from aggressive conspecifics and predators. More boats, especially private recreational boats, were found in the shallower waters, indicating that nursery groups are at greater risk from encounters with boat motors or recreational fishing gear in such areas. Group focal follows of at least 30- minutes were conducted on 56 nursery groups. Calves engaged in significantly more high energy behaviours (displays and head first re-entries) than non-calves in nursery groups. These groups were predominantly resting and compactly organized (interanimal distance less than 1 adult body length). Nursery groups showed a high level of synchrony, with 44% of groups synchronizing their submergence and surfacings for most of the focal follow. Median group size was 14, with a minimum of 2 mother-calf pairs to a maximum of 50 mother-calf pairs. A total of 260 individuals were catalogued as members of nursery groups during the two field seasons. Of these, 112 individuals were seen in nursery groups on at least two different days. Some individuals photographed with young calves in nursery groups off Kaikoura were later photographed in Admiralty Bay, 275 km northwest of Kaikoura. Other individuals photographed together in nursery groups in 2005 were also together in nursery groups in 2006.