Population biology and the effects of tourism on Hector's Dolphins (Cephalorhynchus hectori), in Porpoise Bay, NZ
Green, Erin Leigh
A small population of Hector's dolphins (Cephalorhynchus hectori) in Porpoise Bay, New Zealand, attracts a single commercial dolphin-watch vessel as well as an increasing number of swimmers who enter the water from the shore. The aims of this study were to collect data on the effects of this tourism, estimate abundance of the population, quantify distribution and alongshore range, and provide recommendations for management. Photo-identification surveys were conducted on 39 and 62 days during the summers of 2001/02 and 2002/03 respectively. Nineteen dolphins were identifiable from naturally occurring markings. Ten of these had been identified during 1995-97, showing dolphins are seasonally resident over the long term. Large variability in the number of times individuals were sighted suggests that some dolphins are resident and others are occasional visitors. Chapman's version of the Lincoln-Petersen mark recapture estimate was scaled up using a mark rate of 46.8 % to provide an abundance estimate of 43 dolphins (95 % Cl = 40 - 48). This estimate was lower than the estimate of 48 dolphins calculated five years ago (95 % Cl = 45 - 55), though confidence intervals overlapped. Theodolite tracking from a land-based station over 189 hours on 48 days during 2001/02 and 190 hours over 56 days during 2002/03 showed dolphins preferred a small area in the southern part of the bay. Overall distribution was similar to that observed during 1995-97. Dolphins became more congregated in the southern part of the bay during successive times of the day from morning to afternoon. Small differences in monthly distribution and distribution in the presence of boats and swimmers observed in 2002/03 were not apparent in 2001/02. Dolphins showed no sign of displacement from the bay since 1997. Over the research summers dolphins in Porpoise Bay spent, on average, 33 % of observation time in the presence of boats and swimmers. This has increased from 24 % in five years. Time spent with swimmers within 200 metres has increased almost three-fold. Analysis of theodolite data showed dolphins approached boats no more frequently than would be expected by chance during 2001/02, but were attracted to boats during 2002/03. Although the duration of an encounter had no effect on the probability of a dolphin heading towards a boat, dolphins became less interested in swimmers with time. Whereas in 1995-97 dolphin pods were found to become tighter in the presence of boats and swimmers, during the current research dolphin pods became more dispersed. In addition, behavioural budgets differed in the presence of tourism, with dolphins 'diving' less and 'milling' and 'socialising' more when near boats and swimmers. Effects were strongest in response to boats and inevitably have some metabolic cost. Boat surveys along the coast comprised the first attempt to document this population's range beyond the bay. High dolphin density was found at Toetoe Bay, 35 km west. Low survey effort meant few conclusions about density to the east could be drawn. Comparison of identifiable dolphins seen in Toetoe Bay showed they comprise the same population as dolphins in Porpoise Bay. Some evidence suggests that dolphins exhibit a seasonal alongshore shift, though higher survey effort is needed to test this hypothesis. Implications of these data are discussed with regard to the establishment of a Marine Mammal Sanctuary in the area. Recommendations to aid the management of this population are proposed and potential avenues for future research are discussed.
Advisor: Dawson, Steve; Slooten, Liz
Degree Name: Master of Science
Degree Discipline: Zoology / Marine Science
Publisher: University of Otago
Research Type: Thesis