Imprisonment under the ice floe (ice entrapment)

What is it?

Imprisonment under the ice floe, also called "sassat" by the Inuit, is a natural phenomenon that affects the narwhal, a tusked Arctic whale.\n\nThis cetacean must regularly come to the surface to breathe air. However, it cannot pierce too thick ice with its blowhole.\n\nWhen winds and currents suddenly close the areas of open water (polynyas or channels) on which narwhals rely to breathe, an entire group can find themselves trapped far from any sufficient opening to the open air.\n\nThis is not an infectious disease but a serious environmental accident, which can lead to the death by asphyxiation of a large number of animals in a few days if no exit does not emerge.

Trapped narwhals often gather very densely around the only remaining air hole, sometimes in dozens or hundreds.\n\nWe observe intense agitation near the opening, animals scrambling to breathe, visible fatigue and increasingly slow movements in the most weakened individuals.\n\nThe skin and snout may show wounds, scratches or sores due to repeated rubbing against the sharp edges of the ice in an attempt to enlarge the hole.\n\nIn prolonged cases, some animals show signs of extreme exhaustion, difficulty breathing and may eventually drown or die from asphyxiation from lack of oxygen.

Commonly observed signs

These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.

Causes and risk factors

Entrapment occurs when a rapid change in temperature, wind or current causes the sudden formation of ice over large areas of open water normally used by narwhals to move and breathe between two areas of open sea.\n\nNarwhals migrate by following polynyas and leads of thin ice. If these corridors close earlier or faster than expected, particularly during a sudden cold at the start of winter, the animals no longer have time to reach the open sea before complete freeze-up.

Groups of narwhals that migrate late in autumn or that stay too long in Arctic bays and fjords before the winter break-up are most exposed.\n\nA harsh winter with rapid ice-up, a lack of wind to keep the polynyas open, or a significant distance to travel to the open sea greatly increase the risk.\n\nYoung narwhals and already weakened animals are less tolerant of a prolonged episode of trapping.

Diagnosis and care

Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.

Treatment

There is no medical treatment for this phenomenon, which is an environmental accident and not an illness.\n\nThe only possible interventions are logistical and human: enlargement of the existing hole using tools, attempt to open a channel towards the open sea, or in certain exceptional cases use of controlled explosives to fragment the ice.\n\nThese operations are carried out by local or scientific teams and are not a classic veterinary procedure.

Prevention

Possible complications

Without rapid intervention, the outcome can be the death of a large number of animals in the group by asphyxiation or drowning.\n\nWeakened animals also become easier prey for polar bears who spot these air holes and take advantage of the situation to chase away exhausted narwhals.\n\nSurvivors may present skin wounds and lasting exhaustion after the episode.

When to see a veterinarian

Prognosis

The prognosis depends above all on the speed with which an exit to the open sea can be re-established, naturally by wind or currents, or artificially by human intervention.\n\nIf the air hole closes completely or if the nearest free zone is too far away, mortality within the trapped group can be very high in the space of a few days to a few weeks.\n\nRapid intervention and a mild climate can, on the other hand, allow a large part of the group to reach the open sea and survive.

Frequently asked questions

References

WOAH — Organisation mondiale de la santé animale (ex-OIE)

Content reviewed by the TunisieVet editorial team · Updated 03 September 2026