–Isles Seal–

Isles Seal
Categories: Flora and Fauna

This article was written by Vyberia

The Isles Seal, (Phoca vitulina) is a true seal found along marine coastlines of The Western Isles.

Isles seals are brown, silvery white, tan, or gray, with distinctive V-shaped nostrils. An adult can attain a length of 1.85 m (6.1 ft) and a mass of 132 kg (290 lb). Blubber under the seal's skin helps to maintain body temperature. Females outlive males (30–35 years versus 20–25 years). Isles seals stick to familiar resting spots or haulout sites, generally rocky areas (although ice, sand, and mud may also be used) where they are protected from adverse weather conditions and predation, near a foraging area. Males may fight over mates under water and on land. Females bear a single pup after a nine-month gestation, which they care for alone. Pups can weigh up to 16 kg (35 lb) and are able to swim and dive within hours of birth. They develop quickly on their mothers' fat-rich milk, and are weaned after four to six weeks.

The global population of Isles Seals is 350,000–500,000, but subspecies in certain habitats are threatened. Once a common practice, sealing is now illegal in many nations within the animal's range.

Description and Identification
Individual Isles seals possess a unique pattern of spots, either dark on a light background or light on a dark. They vary in color from brownish black to tan or grey; underparts are generally lighter. The body and flippers are short, heads are rounded. Nostrils appear distinctively V-shaped. As with other true seals, there is no pinna (ear flap). An ear canal may be visible behind the eye. Including the head and flippers, they may reach an adult length of 1.85 meters (6.1 ft) and a weight of 55 to 168 kg (120 to 370 lb). Females are generally smaller than males.

Distribution and Habitat
Isles Seals prefer to frequent familiar resting sites. They may spend several days at sea and travel up to 50 km in search of feeding grounds, and will also swim 100+ miles upstream into fresh water in large rivers. Resting sites may be both rugged, rocky coasts, such as those of the Gael or the shorelines of Argus, or sandy beaches. Isles Seals frequently congregate in harbors, bays, sandy intertidal zones, and estuaries in pursuit of prey fish such as salmon, menhaden, anchovy, sea bass, herring, mackerel, cod, whiting and flatfish, and occasionally shrimp, crabs, mollusks, and squid. Seal subspecies of either Europe or North America also exploit deeper-dwelling fish of the genus Ammodytes as a food source and Pacific subspecies have been recorded occasionally consuming fish of the genus Oncorhynchus. Although primarily coastal, dives to over 500 m have been recorded. Isles Seals have been recorded to attack, kill and eat several kinds of duck.

Behaviour
Isles seals are solitary, but are gregarious when hauled out and during the breeding season, though they do not form groups as large as some other seals. When not actively feeding, they haul to rest. They tend to be coastal, not venturing more than 20 km offshore. The mating system is not known, but thought to be polygamous. Females give birth once per year, with a gestation period around nine months. Females have a mean age at sexual maturity of 3.72 years and a mean age at first parturition of 4.64. Both courtship and mating occur under water. Pregnancy rate of females was 92% from age 3 to age 36, with lowered reproductive success after the age of 25 years.

Birthing of pups occurs annually on shore. The timing of the pupping season varies with location, occurring in February for populations in lower latitudes, and as late as July in the subarctic zone. The mothers are the sole providers of care, with lactation lasting 24 days. Researchers have found males gather under water, turn on their backs, put their heads together, and vocalize to attract females ready for breeding. The single pups are born well developed, capable of swimming and diving within hours. Suckling for three to four weeks, pups feed on the mother's rich, fatty milk and grow rapidly; born weighing up to 16 kilograms, the pups may double their weight by the time of weaning.

Isles seals must spend a great deal of time on shore when moulting, which occurs shortly after breeding. This onshore time is important to the lifecycle, and can be disturbed when substantial human presence occurs. The timing of onset of moult depends on the age and sex of the animal, with yearlings moulting first and adult males last. A female mates again immediately following the weaning of her pup. Isles seals are sometimes reluctant to haul out in the presence of humans, so shoreline development and access must be carefully studied in known locations of seal haul out.

In comparison to many pinniped species, and in contrast to otariid pinnipeds, seals are generally regarded to be more vocally reticent. However, they do utilize non-harmonic vocalizations to maintain breeding territories and to attract mates during specified times of year, and also during mother and pup interactions.

Annual survival rates were calculated at 0.91 for adult males, and 0.902 for adult females. Maximum age for females was 36 and for males 31 years.