Fourth International Orca Symposium and Workshop - CEBC - CNRS

(i.e. three to five months later than their peak in abundance around the sub-Antarctic islands).
The observed difference in the timing of peak abundance in killer whales might be related to
dispersing killer whales passing through different latitudes at different times (Mikhalev et al.
1981).
Group size - The overall mean group size for the whole study period was approximately
four individuals (Keith et al. 2001; Condy et al. 1978). Elsewhere group sizes varied between
1-15 individuals, with an average of three animals (Baird & Dill 1995), while Mikhalev et al.
(1981) found the most frequent group size to be six to eight animals, although the numbers
varied between one to several hundred animals.
Sex and age composition - Adult females predominated (Keith et al. 2001) whereas
Condy et al. (1978) calculated that killer whales had a sex/age composition of 28.7% adult
males, 21.4% adult females, 24.7% subadults, 7.8% calves and an unidentified class of 17.4%
at Marion Island. However, comparison between studies is complicated due to the difficulty in
distinguishing between a subadult male and an adult female.
Diurnal sighting frequencies - Killer whales were only observable from dawn to dusk
with a peak of opportunistic observations during late afternoon (Condy et al. 1978; Keith et
al. 2001), a probable result of increased human activity around the base station at that
particular time of the day. The dawn-to-dusk surveys (DDUs), on the other hand, produced a
relatively constant distribution of sightings throughout the day (Keith et al. 2001; Pistorius et
al. 2002).
Photogrammetry - The Defran et al. (1990) method for photogrammetry could only be
used on a few individuals that did possess unique, useable markings. The Heimlich-Boran
(1986) method suffered from the varied placing of a base line (BL), but the methods devised
(Keith et al. 2001) provide a quantitative way to position the BL. It may only become evident
after obtaining improved photographs, whether the proposed new adapted methods (Keith et
al. 2001) will improve the photogrammetric analysis method of Heimlich-Boran (1986).
Photo-identification - Many of the photographs of the killer whales were of poor quality
and taken from a great distance which made reliable identification difficult (Keith et al.
2001). The opportunistic and sporadic nature of photographing the killer whales at Marion
Island precluded all of the killer whales being photographed. Due to the nature of the
photographs, which concentrated on individuals, groups could not be distinguished from the
photographs. One female with distinct markings on the dorsal fin, first identified in 1973, was
still present around the island in 1993, at an age in excess of 20 years.
Population size - We identified 26 whales in seven pods during the early morning to late
afternoon sightings on the island-wide vigil (13 December 2000). A second method indicated
that 29 individuals moved north past the base station between 15h28 and 17h55, while a third
estimate of abundance suggested that 20 killer whales were seen in front of the base station,
three at Archway, and three were seen at 16h02 approaching from the west at Pinnacles
(Pistorius et al. 2002). Therefore, we think that there were between 25 and 30 killer whales
hunting around Marion Island during their peak presence in early December 2000.
Human impact - Marion Island has recently been proposed as an eco-tourism destination
(Heydenrych & Jackson 2000) and killer whale ‘watching’ could become a realistic tourist
attraction. Looking solely at the seasonal and diurnal pattern of the occurrences, “orca”
FOURTH INTERNATIONAL ORCA SYMPOSIUM AND WORKSHOPS
SEPTEMBER 23-28 2002, CEBC-CNRS, France
36