This past summer saw an unprecedented number of dead whales wash up on the shores of Ireland, Iceland, and western Scotland – and experts don’t know why.
Since the beginning of August, some 80 Cuvier's beaked whales (Ziphius cavirostris) and several Sowerby's beaked (Mesoplodon bidens) and northern bottlenose whales (Hyperoodon ampullatus) have been found beached, the largest unusual mortality event (UME) of beaked whales anywhere in the world. To put the number into perspective, it is roughly 10 times the number wildlife officials expect to see in a whole year and yet it may only be the tip of the iceberg. The good news is that the strandings now appear to have stopped.
"We know very little about any species of beaked whale in the NE Atlantic but what we do know is that they are not abundant and this mortality could be of conservation concern and not just a welfare issue," a spokesperson from the Irish Whale and Dolphin Group explained in a statement.
According to the group, the 80 plus whales found are probably just a fraction of the total number of those that have died in the UME. Based on a French study that calculated the ratio of bycaught dolphins that make landfall (8 percent) versus those that don't (92 percent), as many as 1,000 whales may have died. What's more, because Cuvier's beaked whales are found further from the shore and sea level than bycaught dolphins, the group says even that 1,000 may be an underestimate.
So far, experts have not been able to confirm a cause of death, though they think it is unlikely to be plastic ingestion or disease due to the geography and timeframe of the strandings. Instead, they suspect ocean noise caused by human activity is to blame.
Beaked whales – and the elusive Cuvier's in particularly – seem to be extremely sensitive to the sonar waves produced by naval ships on the lookout for enemy subs, and past strandings have been linked to military exercises in the Atlantic and Pacific. They may be affected directly (death or injury due to permanent or temporary hearing loss) or indirectly (decompression sickness or the "bends" triggered by changes in behavior).
The UK government has launched an investigation into the cause of the deaths and the Irish government has said they will fully cooperate. Unfortunately, the whales were discovered in extremely poor condition (which suggests they have been drifting in the water for some time) and so it may be that we never find out.