Grey seal

(Halichoerus grypus), gråsäl (SWE), halli or harmaahylje (FIN)

The grey seal is the most numerous seal species in the Baltic Sea. Photo: Marcus Wikman

The grey seal is the biggest of the seal species in the Baltic Sea. The males can reach up to 2.3 meters in length and weigh up to 300 kg. The length of the females is about two metres and their weight nearly 200 kg. The colour and patterning of these species' coats vary by gender and age. Grey seals become mature at the age of between 3 and 6 years, the female earlier than the male.

The most typical breeding environment for the Baltic Sea grey seals is ice. Their pups are born between February and March. The grey seal usually gives birth in the zone of ice floats between the pack ice and open sea. If ice is not available, grey seals can also give birth on land. On ice, the females mostly give birth on their own, but, when in groups, around islets. The length of a newborn pup is one metre and the weight between 10 and 12 kilograms. Nursing lasts approximately 17 days during which the pup can increase 2 kilograms per day in weight. Towards the end of the nursing period the female will come to heat.

Mobility and a wide seasonal migration range are typical of grey seals. A grey seal has been observed to move even over a distance of 100 km in 24 hours. The daily movement range of the grey seal, however, is less than 10 km.

Illustration: Grey seal's diving patterns
It has been observed that the Baltic grey seal can dive to a depth of more than 100 metres. Most of the dives last less than 10 minutes and reach the depth of 25 metres on average. The deepest dives of this individual have reached 50 metres in depth.

Photo: A grey seal trapped with a pontoon trap before being transported to the shore to be equipped with a GPS-GSM transmitter.
Photo: Esa Lehtonen

Research projects

Harmaahylkeiden elävänäpyynti- ja talteenottomenetelmän kehittäminen sekä ongelmayksilöiden liikkumisen ja käyttäytymisen seuranta (in Finnish)

Itämeren hylkeiden ekologia (in Finnish)

Harmaahylkeiden elävänäpyynti kalanpyydyksillä (in Finnish)

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