Me, in the field

Jakobina Arch


Email: jarch@is2.dal.ca


The following is the abstract from my MSc thesis.

I examined group function for northern bottlenose whales, Hyperoodon ampullatus, in the Gully through analysis of group structure and disturbance reactions. Bottlenose whales in this population are found in close, coordinated groups within a bodylength or less of each other. Nearest neighbor pairs are a median of 4.82 m (range=1.64 to 12.36 m, n=65) apart from each other, with one swimming ahead by an average of 2.75 m (S.D.=1.90, n=48) and a median angle between them of only 9.4 (range=0.1 to 59.6 , n=161). This structure is probably mediated by visual contact, because all whales in a group are well within visual range of their nearest neighbor and because social sounds are rare if they exist at all. Males and females swim significantly closer to their own sex than to the other. Because females and immatures are most often found in groups without males than vice versa, females are most likely the ones benefiting directly from group membership while males take advantage of these groups for reproductive purposes.

Females and immatures may benefit from groups through the opportunity to provide more care for the young and/or protection of the young from predation. The most apparent reaction to disturbance was an increase in swimming speed (estimated from the height of the body out of the water in identification photographs). While this may not be the reaction used against predators, both anthropogenic (biopsy and tagging attempts) and natural (the arrival of other cetacean species) sources of disturbance resulted in this coordinated escape response.

Disturbance was also examined in order to find measures which could be used to test the impact of human activities around the Gully on this small population of whales. Of the measures tested, estimated swimming speed from height out of the water and encounter length could both be useful for testing the impact of increased development in the area.


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Last Updated April, 1999 by Jakobina Arch