| Summary: | The social organization and population structure of northern bottlenose whales (Hyperoodon ampullatus) in the Gully was studied from 1988--1997 using photo-identification techniques. While all members of the population possess some natural marks on the dorsal fin and surrounding flank suitable for photo-identification, only 66% (+/- 5%) of the individuals have marks which last for periods of years. Thus analyses which include matches over periods of years were restricted to those individuals with reliable marks, and the results scaled to account for the remainder of the population. Photographic techniques could also be used to reliably assign individuals to age/sex classes based on the development of secondary sexual characteristics in the melon profile. Groups of northern bottlenose whales (individuals within five body lengths of each other and showing coordinated behaviour) were likely to contain interacting individuals, thus presence within the same group was used to define a social association. Groups of bottlenose whales were small (mean 3.04 +/- SD 1.86, n = 1.281) and often composed of mixed age/sex classes. Most of the associations within the groups quickly dissociated, although sub-adult and mature males formed preferential associations with other members of their same age class and some of these associations lasted for periods of years. Female and immature males formed a loose network of associations with no preferential associations with other adult-sized animals. Calves were born in June, July and August in the Gully, although births may have occurred outside these months. Probable mothers could be identified based on association patterns for several calves and juveniles, although not all young animals which were repeatedly observed could be assigned to a probable mother. Young bottlenose whales associated with individuals who could not be their mother (e.g., males) even when no females were present, indicating that babysitting may occur although the costs, benefits, function and frequency of babysitting could not be determined. The Gully population was small (130 individuals, 95% c.i. 104--170 from left side identifications; 122, 95% c.i. 100--157 from right side identifications) and may be largely distinct from other populations of bottlenose whales in the North Atlantic. Mortality, mark change and permanent emigration was estimated at 12% per year (95% c.i. 8--17) and there was no significant change in population size over the nine year study. Over the summer field season, individuals emigrated from, and re-immigrated into the Gully, spending on average 10 +/- 5 days in the Gully. Estimates of the number of days spent outside of the Gully were imprecise and variable, however most individuals were resighted in the Gully in subsequent years. On average one-third of the population (43 +/- 10 individuals) were present in the Gully at any given time. Many aspects of the social organization and population structure of northern bottlenose whales in the Gully resembled those of bottlenose dolphins ( Tursiops truncatus) in Monkey Mia, Australia and Sarasota, Florida. The similarities may result from similarities in the low variability of food resources in these study areas and horizontal spatial scale, although this hypothesis requires specific testing. Thesis (Ph.D.)--Dalhousie University (Canada), 1999.
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