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Why do whales mass strand?

Why do whales mass strand?

The whole phenomenon of mass stranding is scarcely understood at all. This event is by no means uncommon or of only recent occurrence, though it is confined to certain pelagic species of cetaceans. Bottlenose dolphins and killer whales, for example, almost never mass strand, while sperm whales and Atlantic white-sided dolphins, which are presumed to be equally intelligent animals, quite often do. The most likely candidate for a mass stranding along the Irish coastline is the long-finned pilot whale Globicephala melas. Typically most members of the stranding group appear to be perfectly healthy animals, though the first to strand may be sick or injured in some way. The social cohesion of the vulnerable species is supposed to lead the remainder of the group to strand as if in sympathy. Evolutionary biologists find this argument implausible, as those whales which tended to strand en masse would obviously not succeed in passing their genes on to subsequent generations and so this behaviour would not be selected for. It also leaves open the question of why the ‘lead animals’ should strand in the first place.
A number of possible causes have been proposed by scientists, but none of them are particularly convincing. The usual theme is that the whales’ navigation systems are thought to have broken down in some way. Perhaps they are suffering from a parasitic infection of the ear passages, so their echolocation doesn’t work. So why should that land them up on specific beaches instead of wandering around in circles? Or maybe their echolocation doesn’t work so well on gently sloping sea-bottoms – after all, the species which tend to mass strand are more used to deep water. And yet we know that cetacean sonar is vastly more sophisticated than the man-made variety, which detects shallow ground with perfect ease. Again, it has often been claimed that whales follow electromagnetic patterns in the sea-bed and that these shift over time, so confusing them. However, there is not much evidence either that whales depend on electromagnetic guidance or that electromagnetic fields change in sudden and well-defined ways; but let us for the moment accept both suppositions. That would be a bit like a new roundabout being built on a road you were used to driving on. You might be confused for a minute when you met it for the first time, and you might even take a wrong turn before turning back to your original route, but you would hardly try and drive through the nearest shopping centre or across a river in your determination to get to your destination.
A slightly different hypothesis is that whales get over-involved in the pursuit of fish they are feeding on and unexpectedly find themselves in shallow water. We don’t find this idea any more believable, and there is no evidence for it either, in fact many whales are known to have stranded with empty stomachs and in areas totally lacking their normal prey species.

The problem with all the ideas proposed above, whether singly or in combination, is that they assume that whales are stupid. If we are prepared to credit them with the intelligence of an average shoal of herring then we can see that none of the suggestions are adequate, either individually or in combination, to explain how a group of aquatic animals could make such a crass ‘mistake’ as to land themselves high and dry on the shore. Whales of all species are perfectly adapted over tens of millions of years for living in the sea, with all the variety of topography and conditions that implies. And yet, from time to time a group of them swims quite deliberately into shallow water and eventually ends up on the beach, where they die. If returned to the sea, some of these whales often show remarkable persistence in restranding themselves. We don’t know why this should be - and we should not be afraid to admit that we don’t know. It is at least a possibility worth considering that it represents a deliberate choice by conscious and intelligent animals acting under impulses of which we have little or no conception.

What should we do with stranded whales?
If and only if it is possible to return the whales to the sea without injuring them, we are not against trying this, one time only. Even would-be suicides are sometimes glad to be brought back from the brink. But a stranded whale is very hard to move without specialist equipment and good organisation. Dragging a cetacean across the beach, whether by hand or with tractors or boats can only kill it. It is just a matter of how long it will take to die after you go home satisfied with your day’s work. The whale's body is designed to be supported by water and cannot be treated like a sack of potatoes. Tying a rope around its fins or tailstock is like tying a rope around a man’s neck and should not be considered. So the whale must be lifted and carried. But that is not easy either. In the case of a small ceatcean, if it is possible to rock a whale gently from side to side and introduce a number of webbing straps (not ropes, of course) under its body, and to protect the fins and tail separately from being dragged or caught, then a JCB or HiMac may be used to carry the animal to the sea. Picking it up in the digger’s bucket is not an option, of course. The best method for pilot whales is to use the purpose-designed stretchers with inflatable sides and holes for the fins which were developed for the purpose by Project Jonah team in New Zealand. Two sets of these are kept on the west coast by the Irish Whale and Dolphin Group, one in Kilrush and one in Cork, and they can be delivered on site anywhere along the coast within a couple of hours. Plenty of man- and woman-power is needed to ease a three or four tonne whale through the surf, and people may need to stay in the water with the refloated whale for some time and support it until it recovers. Therefore you need lots of calm and competent people with wetsuits or drysuits.
In any case, whatever equipment and personnel you have available, it is far better to wait until the next high tide before attempting a refloat. A cetacean can survive up to 2 days out of water provided it is cooled and not stressed. Otherwise the main danger is that its internal organs get crushed by its own bodyweight. Therefore the immediate priority should not be moving the animal but making it comfortable. It must be continually bathed in water, so you need lot of people and buckets if you have a mass stranding. Stranded whales may also need protecting from too many curious people and their dogs. If it is possible to dig a trench around the whales and fill this with water, it can help to support some of the animal's weight which will in turn increase its survival chances.

If there are too many whales, or you are dealing with a bigger species, or you don’t have enough of the right equipment available, then you cannot hope to refloat all or any of them without critically injuring them. None of us wants to see an animal die. But that is exactly what is going to happen, whatever you do. This also applies if a whale repeatedly restrands. The only question then is whether we are prepared to allow the whale the dignity of dying in the place and in the way it has to some extent chosen, or whether we are going to avoid reality by using whatever brute force we can throw at the situation to drag the dying animal back out to sea again. Once we have faced our own feelings about accepting the death, then we can put our efforts into making the whale as comfortable as we can while it is dying. We can try to keep it cool and unmolested by predators, we can hold it upright if it is in shallow water so that it can breathe, we can try to comfort it in whatever way we know best. This may be a long and painful process, but it may also be strangely transformative. Lyall Watson recounts a moving experience of staying up all night talking to a dying sperm whale he was powerless to help otherwise. That is at least more humane than dragging an animal back out to sea and leaving it to die somewhere along the coast while we go home to our beds.

Some people think that mass strandings involve a lead animal which beaches itself and then emits distress calls which attract the rest of the group to do likewise. They accordingly propose killing the lead animal before trying to refloat or divert the others. Even ignoring the suppositions inherent in the original hypothesis and the fact that nobody really understands what any whale squeaks mean (i.e. that small part of the whale’s vocalisation which is audible to humans), there are several flaws in this approach. It depends firstly on knowing which animal stranded first, and if you were there to see that, then you were there to prevent the remainder following. And I say ‘killing’ because we do not have a good method of euthanasia for cetaceans. The thick blubber, large size and hard to guess at internal anatomy mean that shooting with conventional firearms is unlikely to lead to a rapid or painless death. The only recommended method of mercy killing is injection of a veterinary drug known as Immobilon, which ideally requires a 25cm long needle and the skills of an experienced vet. This method is not without risk to the vet adminstering the drug and his helpers and it should only be considered if it seems very clear that a single animal is leading the others to their death – and even then it should not automatically be assumed that we have this right of judgment, understanding as we do so little of the reasons behind cetacean strandings. The main course of action we propose in this situation, therefore, is to make every effort to divert the other whales first.

© 2002 Graham Timmins

For more information see the Irish Whale and Dolphin Group website.

Date Posted: 25/03/2002
Date Edited: 27/03/2008
Topic: General
Library: Current
Keywords: pilot whale stranding mass
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