The ecology of bottlenose dolphins in the Moray Firth, Scotland : a population at the northern extreme of the species' range
The distribution, social structure, epidermal lesions and population size of the bottlenose dolphin population in the Moray Firth off the coast of Scotland were studied between 1990 and 1993. Dolphins were seen in the inner Moray Firth all year round: numbers were low in winter by rose in late spring to peak in summer. All parts of the inner Moray Firth were frequented, but three areas, at narrows which had deep water and strong currents, were favoured. Areas used by the dolphins varied seasonally: in winter the outer parts of the inner Moray Firth were occupied, whilst in summer all areas were used. The spring increase in numbers and changes in distribution occurred together as part of a general redistribution of individuals (demonstrated using photo-identification methods) in the inner Moray Firth. Animals entering the inner Moray Firth from outside stayed further towards the open sea than previously resident animals. Seasonal migrations of fish, elevated temperatures and sheltered waters may explain the summer increase in use, whilst social factors between groupings may have maintained the horizontal separation of different segments of the dolphin population. Individuals ranged widely (average range 123 km2) and rapid, long distance movements, across the Moray Firth, were observed (190 km in 120 hrs). The dolphins were highly social, with 99% being seen in schools. These ranged in size from 2 to 46 individuals (median 4.5). School sizes were not unusual compared with other populations. They were found to be bigger in winter and in more open sea environments. Average levels of social cohesion between individuals were low. Close bonds occurred only between females and their calves and lasted for at least four years after birth. Each female loosely associated with a network of other females. The associates of each female remained similar over at least three years and were the result of preferential associations rather than coincident ranges.