The behavioural ecology of young harbour seals in the Moray Firth, NE Scotland
Studies of the behavioural ecology of young harbour seals were made in the Moray Firth, NE Scotland. The terrestrial behaviour of mothers and pups were recorded at an intertidal haul-out site, using scan and focal-animal sampling. A large percentage of the seals' time was spent resting and suckling. Suckling was influenced by tidal state with peaks at the beginning and end of haul-out. Suckling sessions were shorter for younger pups but overall time spent suckling did not differ with age. Pups became increasingly responsible for maintaining the suckling relationship and pair proximity as lactation progressed. A rapid, non-invasive method of distinguishing seals in their first year from older age classes were determined, based on mean hair widths. Mean hair widths feel into two distinct groups, and were significantly greater for older age classes. The diving behaviour and foraging distribution of juvenile seals was compared with that of older animals. Dive duration was positively correlated with body size and time at the surface was negatively correlated with size. Most dives fell within theoretical aerobic dive limits. Body size restrictions on diving performance were predicted to limit the bottom time and dive depth of juveniles compared to adults. Whilst the foraging locations of juveniles overlapped with those of adults, juveniles, unlike adults, did not forage in water greater than 40 m in depth. Juveniles exhibited a marked shift in foraging area use, apparently in response to an influx of overwintering clupeids. Growth in length and weight during the first year of the life was linear. Males were longer and heavier than females during this period, but grew at the same rate. Between-year changes in food availability led to increased length and weight of yearlings. Mean lengths of adults were lower than those of other populations, although growth rates were amongst the highest.