Distribution, movements and abundance of Hector's dolphin around Banks Peninsula. (1992)
AuthorsSmith, Susan Leslieshow all
New Zealand's first Marine Mammal Sanctuary was established around Banks Peninsula in 1988, to protect Hector's dolphins from entanglement in gillnets. Understanding distribution and movements of Hector's dolphins inhabiting Banks Peninsula has important implications for their effective management. The need to assess the effectiveness of restricting gillnetting also underscores the need for ongoing estimates of the size of the Banks Peninsula Hector's dolphin population. I analysed spatial and temporal movements of distinctive Hector's dolphins identified around Banks Peninsula. A substantial number of dolphins I identified in the northern portion of Banks Peninsula have been sighted in the southern portion of Banks Peninsula but none of the individuals I identified have been sighted north or south of the peninsula (Slooten, Dawson, Stone and Yoshinaga, unpub. data). These results suggest that Hector's dolphins resident around Banks Peninsula, are a single interacting population. I assessed the applicability of mark-recapture methods using photo-identification of distinctive individuals to estimate the size of the Banks Peninsula population of Hector's dolphins. The maximum average capture probability for Hector's dolphins around Banks Peninsula during my study was in the range of "poor" data. During my study, small sample size and low recapture rates of identified dolphins was generally the case. These results indicated that numbers of Hector's dolphins around Banks Peninsula cannot be estimated reliably from mark-recapture methods with the data which is currently available. I conducted surveys to estimate the abundance of Hector's dolphins in the northern portion of Banks Peninsula. I also used survey data to examine the temporal and spatial distribution of dolphins in the study area. No more than 123 dolphins were counted on a survey and on approximately 70% of surveys, fewer than 41 were counted. I found no significant difference in number of dolphins counted during November to March, suggesting that conducting surveys during this period is an appropriate sampling strategy for estimating abundance. There was a highly significant association between abundance and location, indicating it is inappropriate to extrapolate abundance estimates from one area to another based on a simple density 1 area relationship. Estimates of abundance for Hector's dolphins in the northern portion of Banks Peninsula for 1990/91 and 1991/92 were in the range of previously reported estimates for Banks Peninsula.