Donal Hickey: Mystery of dead whales

Mystery surrounds the reason for the stranding of an unusually high number of whales along the west coast but given man’s growing propensity for polluting the oceans, human interference cannot be ruled out.

Last month, 16 Cuvier’s beaked whales were found washed up dead in counties Galway, Mayo, Sligo and Donegal.

The Irish Whale and Dolphin Group (IWDG) says nothing on this scale has been recorded for this species in Ireland before, although there were 11 recorded strandings over several months in late 2014 and 2015.

In previous years, there might be just a few, or none.

No cause of death has been established for any of the latest strandings, mainly because all the animals were in poor condition.

Previous studies have suggested that only a small number of dead animals actually get washed in and recorded, so the true number of dead may be much higher.

The IWDG’s Mick O’Connell says the condition of the carcasses suggested all may have died around the same time.

This makes causes such as disease and plastic ingestion unlikely as these would tend to be spread out over a longer period and geographical range.

He also believes large-scale fishing activity is an unlikely cause.

He noted from events globally that beaked whales are susceptible to death or injury directly from extremely loud, man-made noise in the oceans, such as that produced by navies or work in surveying the sea floor.

Such noise can lead to temporary or permanent hearing damage in whales and changes in their behaviour.

“Mass strandings of beaked whales coincidental with naval exercises have been recorded in Greece, the Canaries and the Bahamas. The Irish navy does not use these types of sonar,’’ says Mr O’Connell.

“While no definite cause has been established, this needs to be recognised as an unusual mass stranding event in an effort to identify the cause(s) and perhaps prevent a future recurrence.’’

Plastic now pollutes almost every corner of the globe and around eight million tonnes of it ends up in the oceans each year.

Last year, we had the sad spectacle of a beaked whale which stranded near Bergen in Norway.

Thirty plastic bags, and lots of smaller plastic items, were found in the whale’s stomach, preventing the digestive process.

It had to be put down.

Cuvier’s beaked whales are not seen alive that often and most information about them comes from examining stranded animals.

They live in deep water offshore, typically around canyons near the edge of the continental shelf, and regularly dive for 20-40 minutes following a series of breaths at the surface.