Pilot whales and New Zealand strandings.

By Paul Robinson - 15 Feb 2015 12:36:0 GMT
Pilot whales and New Zealand strandings.

Happier times for Globiocephala melas, as a mother and baby enjoy their open ocean habitat.Pilot whales image; Credit: © Shutterstock

Why do pilot whales and many others strand themselves so often, although the closely related killer whales rarely do? The basic argument among marine zoologists is that some of the pod could be sick and are first to place themselves in shallow water or on a beach. The others communicate with them and follow their lead. The latest stranding in New Zealand is at a well-known and, indeed, well-named outcrop of land for the whales, Farewell Spit, at the strategic northerly point of South Island. Florida and Scotland have lengthy and historic records of similar beachings, with an infamous stranding on Cape Cod in 1902. Orcadians may recall their forebears calling,the beasts from the sea, --- for food!

In many places, the pilot whale is the most common whale, although dolphins will usually outnumber them and are strictly speaking more closely related than the larger whales. Overcrowding has not been related as a factor in these losses however. Disease certainly has, and with marine mammal accumulations. We could have come across a seasonal spurt of disease-related deaths. As pilot whales, sperm whales and other deeper-sea species are the usual strandees, the interspecific argument has also been made. These whales may simply be following dolphins into the shallow water. They could consume many more fish if they follow the adept dolphins, as we know they tend to.

Research into noise pollution on the US Pacific coast has also been quite fruitful, in that 17 local blue whales interrupted deep dives, at great expense to their energy requirements. More sinister is the implication that military LFA sonar use often causes whales to beach soon afterwards. The decompression-like damage to the whales concerned was caused by massive haemorrhaging around the ears. We are talking about the loudest noises ever put into the ocean (it is a way of detecting submarines.) Other studies elsewhere have been more general, with the distance travelled by engine sounds being especially significant to the nearby cetacean fauna. Jet skis and even nearby road noise have also been implicated in whale response to various frequencies.

The weather was blamed for some stranding in one recent study in Tasmania, as whales follow squid and other prey into shallow water when cold currents carry them there. Beaches have very gentle slopes to hinder the animals' echolocation, as has been noted in other Australian strandings. The explanation is that no echo is audible because the sounds become less and less intense.

The only good news at the moment is that the New Zealanders, skilled at this after many years of practice have persuaded lead whales into deep water with possibly 60 others, leading and following. If these survive, and no euthanasia is necessary, it will be a great success. The species concerned, Globiocephala melas is common, but personally, I'd like to keep it that way.

Several newspapers are keeping us all updated on the success or otherwise of this operation. Here is the National Geographic take on it.