There are at least 33,400 harbour seals in UK waters. This is based on counts of seals at coastal haul-outs during the moulting period in August. Studies in Scotland and the Netherlands suggest that this number underestimates the total, representing only 60-70% of animals aged one year or older. Applying this correction factor indicates that the total population lies between 48,000 and 56,000.
Adult harbour seals typically weigh 80-100kg, with the males being slightly larger than females, and they can live 20-30 years. They normally feed within a 20-mile area around their haul-out sites and eat between 3-5kg of fish a day depending on prey type.
Typical dives last somewhere between one and three minutes, although one male harbour seal was recorded diving for 30 minutes. Most foraging occurs at depths of 10-50m.
Harbour seals have more rounded faces than grey seals. They have V-shaped nostrils, whereas grey seals have nostrils that are more like parallel lines. At haul-out sites harbour seals tend to space themselves out more compared to grey seals, which group closely together.
The species appears to compete with grey seals at some sites and while grey seal numbers have increased, harbour seal numbers have, in many areas, declined.
In 1998 the spread of phocine distemper virus (PDV) reduced the population of harbour seals along the east coast of England (mainly in the Wash) by 52%.
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