Kernel density estimates of alongshore home range of Hector's dolphins at Banks Peninsula, New Zealand

Knowledge about home ranges is essential for understanding the resources required by a species, identifying critical habitats, and revealing the overlap with anthropogenic impacts. Ranging behavior of Hector's dolphins (Cephalorhynchus hectori) was studied via coastal photo-ID surveys in the Banks Peninsula Marine Mammal Sanctuary (BPMMS) between 1985 and 2006. Univariate kernel density estimates of alongshore home range were calculated for 20 individuals with 15 sightings or more. For each individual, sighting locations were transformed into a univariate data set by projecting sightings onto a line drawn 1 km from the coast and measuring the distance along this line relative to an origin. Sightings were weighted by survey effort. Ninety-five percent (K₉₅) of the density estimate was used as a measure of alongshore home range, and 50% of the estimate (K₅₀) was used to reveal core portions of coastline where dolphins concentrated their activity. The mean estimates of K₉₅ and K₅₀ were 49.69 km (SE = 5.29) and 17.13 km (SE = 1.89), respectively. Four distinct hubs were apparent where the core areas of different individuals coincided. Three of the dolphins' alongshore ranges extended beyond the current northern boundary of the BPMMS, raising fresh concerns that the sanctuary is not large enough. Proposed changes to gill netting regulations, if enacted, will result in the alongshore ranges of all the dolphins in our study being protected.