Male sperm whales (Physeter macrocephalus) in the north Atlantic : insights into movements, distribution, and foraging ecology

Little is known about male sperm whale movements, distribution and foraging ecology subsequent to segregation from their natal groups. Taking the north Atlantic population as its subject, this study attempted to investigate hypotheses that were put forward during whaling times by using a combination of whaling records of male length, stable isotope (SI) analyses of carbon and nitrogen across whale teeth layers and in potential prey (oceanic squid), and distribution data obtained from five years of acoustic surveys in a high latitude region; Regional differences in male length composition in whale catches confirmed some degree of spatial and temporal segregation in male ontogenetic classes. The expected increase in length with increasing latitude was observed, with larger males found generally in the cooler and most productive regions, particularly in mid-summer. The SI profiles in teeth of males stranded in the UK and Ireland showed a decrease in OBC and an increase in 015N with age as predicted, as the animals start segregating into BC-depleted higher latitudes and possibly feeding at a higher trophic level as they grow in size. The isotopic age-group clusters were linked to two key biological benchmarks: the segregation from natal groups at around 9-10 years and the penetration into high latitudes after the age of 20. Profiles' in teeth from males and females from several regions showed variation reflecting differences in ontogeny and environment inhabited, ( confirming the potential of using SI in teeth to compare the life-history and movements of different populations. There was significant regional, inter- and intra-specific variation in SI of oceanic squid. The intra-specific variation was related to mantle length, region, latitude and haul depth, confirming that caution is needed when inferring trophic relationships of higher predators. Putative prey samples analysed for SI should be representative of the main potential sources of variation such as in this study. In the deep waters of the Atlantic Frontier, sperm whales occurred frequently, in high densities, and formed loose aggregations spanning large distances. It was confirmed through the detection of 'creaks' that feeding must occur in. the area. Water depth was the most important factor explaining their local distribution, while temperature also explained some of the variability in the whales' presence, possibly through the effect of meso-scale features (fronts and eddies) on prey organisms, particularly in the Faroe-Shetland Channel. Keywords: cetacean, ontogeny, segregation, dietary history, migration, body size, size dimorphism, age, deep diving species, squid, whaling, stable isotopes, teeth, passive acoustics, satellite imagesEThOS - Electronic Theses Online ServiceGBUnited Kingdo