Grey seals, the "Baltic pups". Deep dive knowledge from the Gdynia Aquarium

Born in late winter and early spring

Grey seals give birth mainly between February and March, when the Baltic is still cold and unpredictable. Females seek quiet, isolated coastal areas and islands to deliver a single pup.

From the very first days, the young are entirely dependent on their mothers. They cannot yet swim efficiently or hunt, so their survival depends on highly nutritious milk containing up to 60% fat - one of the richest milks in the mammal world. Thanks to this, pups can rapidly double or even triple their body mass in just a few weeks.

A race against time: a short learning window

The nursing period is brief. After several weeks of intensive feeding, the pups undergo a short fasting phase before becoming independent. This is the critical transition stage.

During this time, young seals must quickly learn to:

• swim and dive,
• find and catch prey,
• navigate a challenging marine environment filled with predators and changing conditions.

Their ability to adapt in this narrow window determines their survival in the wild Baltic Sea.

The Baltic diving specialist

The grey seal is perfectly adapted to aquatic life. Although clumsy on land, it becomes an agile and efficient predator underwater.

It can:

• dive deeper than 100 meters,
• hold its breath for up to around 20 minutes,
• optimize oxygen use during dives.

This is possible thanks to high concentrations of myoglobin in muscles, which store oxygen and allow prolonged underwater activity.

Life of adults: following the rhythm of the Baltic

After the breeding season, adult grey seals leave coastal haul-out sites and return to open waters, where they spend most of the year feeding and building energy reserves for the next reproductive cycle.

Their lives are closely tied to the Baltic’s seasonal rhythm – temperature shifts, fish availability, and changing ice conditions all shape their survival strategies.

A species returning to the Baltic

Decades ago, grey seal populations in the Baltic Sea were severely reduced due to hunting and environmental pollution. In recent years, however, protection measures have allowed a gradual recovery.

Despite this progress, challenges remain:

• entanglement in fishing gear,
• chemical pollution,
• limited and disturbed breeding sites.

From "pup" to predator: life shaped by the sea

The story of grey seals is one of resilience and rapid transformation. From fluffy, vulnerable pups to powerful deep-diving predators, every stage of life is a test of adaptation.

As the "Deep dive knowledge" from the Gdynia Aquarium series reminds us, the Baltic Sea is far from a calm postcard landscape. It is a demanding, ever-changing environment where even the most endearing beginnings are governed by the strict rules of survival.