Plausible theory for beaching of whales

WE HAVE ALL seen the pictures on television – a massive beached whale lying helpless on the sand, its big soulful eyes staring helplessly while rescue workers frantically try to help.

Sometimes a whole group (pod) of whales beach themselves – on May 31st last year, 55 false killer whales beached themselves near Cape Town (the record number for a false killer whale beaching is 835 animals). Scientists still neither fully understand why they happen nor if we should be particularly worried about them.

Coastal rescue groups find stranded whales and dolphins and try to rehabilitate them but beached whales often die despite all efforts to help them. Just being out of the water can be enough to terminally injure the whale. Beached whales can die simply from the crushing weight of their own bodies which is normally supported by buoyant water. This unsupported weight can damage muscles causing the release of myoglobin, a protein that is normally used to store and transport oxygen. However, when released in this way it is toxic to the kidneys. Whale blubber, normally needed for insulation in cold water, can also severely overheat a beached animal.

Scientists are able to explain whale-beachings only in about 50 per cent of cases. For example, some beachings are obviously the result of the whale having been injured by a collision with a ship. Pneumonia commonly causes beachings in the north-eastern United States. Algal blooms leading to poisonous “red tides” affect whales and other marine mammals.

Other proposals to explain mass-strandings include military sonar, noise from commercial shipping, anomalies in the earth’s magnetic field, the pod blindly following a sick and disoriented leader, difficulty in navigating shallow waters, and more. Military sonar has been implicated in mass-strandings of beaked whales, but not in other species of whales.

The Deafwhale Society (deafwhale.com), a marine mammal conservation group, has proposed a detailed hypothesis to explain mass-strandings that appeals to me, although I am unsure as to the scientific rigour of the hypothesis. The society proposes that most mass strandings are the result of severe injury caused to whales by seismic shock from undersea earthquakes (seaquakes). The Society says that the whale species known to constantly mass-strand themselves all feed on the squid that breed and lay eggs in the bottom water of mid-oceanic ridge systems. Some 90 per cent of all earthquakes occur near those submerged mountain ranges.

Many of these seaquakes release enormous energy to the water above and there are reports of severe damage to ships caught sailing within range of a large event. The whales dive to great depths to feed on squid. They navigate and locate their prey in the darkness using a sophisticated echo-location system. Evolution has equipped this navigat- ional system to withstand seismic shock, but this can be swamped by severe seaquakes.

The injured whales return to the surface and can remain there for a number of weeks recovering. If they recover successfully they return to their diving and feeding. But if they don’t recover they blindly swim with the currents and can cover large distances before eventually beaching on a protruding beach that intercepts the currents. The Deafwhale Society has traced surface currents upstream from mass-strandings and found that, on average, the nearest feeding grounds of the stranded species was about 2,500 miles upstream and right over a mid-ocean ridge.

Many beached whales are badly infected with parasitic worms. Whales naturally carry parasitic worms in their head sinuses, an essential part of the navigational system of whales. The worms eat debris and keep the sinuses clean and ready for diving. But if the membrane lining the sinus gets damaged, as it could by seismic shock, the worms can eat their way into places they shouldn’t be, multiply there and cause major problems.

Beach strandings of whales and dolphins have been reported as far back as Aristottle’s time and in the same locations they occur today. Reports of mass-strandings are increasing, but this does not necessarily mean it is increasing. The reports follow human population movements. As beach areas get more popular and access is developed to beaches previously unfrequented, and as people become more interested in whales and dolphins, reports of beached mammals will increase naturally.

William Reville is associate professor of biochemistry and public awareness of science officer at UCC