Reproductive strategies of male harbour seals (Phoca vitulina)
A large proportion of the pinnipeds, such as the harbour seal, mate aquatically. Female harbour seals are widely distributed during the time they are in oestrus and it is uneconomical for males to monopolise females. Therefore, male distribution and behaviour during the mating season can provide an insight into harbour seal reproductive strategies. Two acoustic techniques are described, the modification and deployment of modified sonobuoys and the design of an acoustic array, used to record male harbour seal vocalisations during the mating season in the Moray Firth, NE Scotland. A large scale acoustic survey of the inner Moray Firth was combined with VHF telemetry to relate the distribution and behaviour of adult male harbour seals to the distribution of females during the summer pupping and mating season. From the beginning of July until mid August, males decreased their mean range size and performed vocal and dive displays. Vocalisations showed clear tidal variations, with a decrease in the mean number of vocalisations towards low tide. Results demonstrate individual variation in vocalisations and display dives. The percentage of time males spent at the surface was significantly related to male body size, with larger males spending less time recuperating at the surface than smaller males. Males were found displaying throughout the whole of the female distribution, from pupping haul-out sites, to foraging grounds, including transit routes between these two areas. A fine scale acoustic study in the Kessock Channel, Moray Firth showed that a maximum of two males displayed in the channel. Display areas were very small, between 40 m 2 and 135 m 2. Males remained faithful to their display site throughout a mating season and over successive years. The distribution and behaviour of the harbour seal is suggestive of an exploded lek mating system.