Abstract
The endangered Hector's dolphin (Cephalorhynchus hectori hectori) has been studied at Banks Peninsula for the past 23 years. For the current project, novel non-invasive tools were developed to examine the demographics and social structure of this population. A laser photogrammetry system was used to obtain dorsal fin measurements in the field. Laser-metric photographs were obtained for 33 identifiable individuals, resulting in a mean CV of 3.71% for fin length and 3.76% for fin height. Dorsal fin length was found to be a better predictor of total length (females r2=0.732, males r2=0.678) than fin height (females r2=0.511, males r2=0.588). Estimating total length from dorsal fin length yielded an average error of 7.29% (males) and 8.34% (females). Age categories (juvenile, intermediate and adult) were assigned to the individuals measured using this technique and this method therefore shows promise in the ability to approximately age Hector's dolphins. An underwater pole-camera system was used to determine the gender of dolphins associated with the research vessel, dramatically increasing (by 4.5x) the rate at which marked individuals could be sexed. There was no significant difference in the number of males and females bow-riding (G=0.02, df=l, 0.75< p<0.90), thus both sexes had an approximately equal opportunity of being sexed. The data support the hypothesis that a 1: 1 sex ratio exists for this population. Gender composition was determined for 43 groups (with ≤ 5 members). There was a high degree of gender segregation, with only 9.4% of groups being of mixed sex. A small sample (n=7) of groups containing mother-calf and mother-juvenile pairs were examined; they were segregated by sex and all non-mother adults were female. Average group size was significantly larger in groups containing calves than for groups without calves (4.45 vs. 3.61; Wilcoxon: Z=7.371, p<0.0001). However if calves were excluded and "adult only group size" compared, groups without calves were significantly larger than those containing calves (3.57 vs. 2.65; Wilcoxon: Z=-6.716, p<0.0001). Mother-calf groups used inshore areas of Banks Peninsula differently to non-calf groups (G=177.34, v=14, p<0.001). Nursery groups used the upper part of Akaroa Harbour less frequently and the mid and outer harbour more often compared to non-calf groups (G=6.83, v=2, p<0.05). This indicates a slight preference for certain areas, rather than distinct nursery areas that are used only by nursery groups. Nevertheless, this preference has implications for the management of this species.