|
Description:
|
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 . |