| Summary: | 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.
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