Are the 'resident' dolphins of Doubtful Sound becoming less resident?

摘要

Patterns of habitat use by wide-ranging animals may change in response to perturbations within their environment. In 2009, a group of 15 bottlenose dolphins, known to be part of the population in Doubtful Sound, New Zealand, were seen in another nearby fiord. This population has been closely monitored since 1990, and this was the first time that a group from Doubtful Sound was seen elsewhere. Since this first occurrence there have been at least 6 other occasions on which 'resident' dolphins were missing for at least 3 d, to later reappear in the fiord. During these absences, the other members of the population were routinely sighted. We use capture-recapture modelling based on photo-ID data to demonstrate a dramatic difference in capture probability between 2005 to 2009 and 2010 to 2011. Given the extremely high capture probability in the first period, and the fact that field effort has significantly increased from 2009 through to 2011, it is unlikely that these groups were within the fiord and simply missed. These findings suggest the possibility that the habitat use of this population has changed to include relatively frequent excursions beyond the fiord complex.