ESR 21:45-54 (2013)  -  DOI: https://doi.org/10.3354/esr00508

ABSTRACT: We studied habitat use by Hector’s dolphins Cephalorhynchus hectori in order to quantify the influences of location, season, time and tide, and to determine how frequently dolphins use inner Akaroa Harbour where unattended gillnetting is allowed for 7 mo of the year (1 April to 30 September). T-POD acoustic dataloggers were moored in outer, mid- and inner Akaroa Harbour to quantify variation in habitat utilisation by Hector’s dolphins over a year. Acoustic detections were analysed via an information-theoretic approach, with model choices made via quasi-Akaike’s Information Criterion. The best model included all 4 factors ‘site’, ‘season’, ‘time’ (since sunrise) and ‘tide’ (time since high tide) and 5 interactions (site × season, site × time, site × tide, season × time, season × tide). Of the interactions, site × season was most important, with seasonal differences being much greater in the inner harbour than elsewhere. Next most important was site × time after sunrise, suggesting diurnal movement of dolphins within the harbour. T-POD data showed a much higher level of use of the inner harbour in winter than was expected, indicating that the current compromise allowing gillnetting in this area poses a genuine risk of entanglement.

KEY WORDS: Hector’s dolphin · Habitat use · Time · Tide · Season