BioEd Online

Researchers have begun to answer the question of how and why a whale died after swimming up the River Thames last week — a rare event that captivated the world's media.

The northern bottlenose whale probably became dehydrated after being unable to find food, says Paul Jepson of the Zoological Society of London, who was part of an unsuccessful rescue effort.

The animal was a juvenile female, probably less than 11 years old, measuring almost 6 metres and weighing several tonnes. Jepson and his team believe that she strayed into the North Sea after "taking a wrong turn at Scotland"; these whales are usually confined to the northern Atlantic Ocean. The whale may have been alone or part of a pack at that point.

Whales of all types are known to make occassional odd turnings that take them away from their usual haunts.

After heading south through the North Sea, the whale turned into the Thames estuary, apparently heading west to search for food. Jepson says that researchers still do not understand exactly how the whale's navigation system works, but one possibility is that they sense Earth's magnetic field much as migratory birds do. If so, the lost whale may have been so intent on a westward bearing that it did not turn back, even when faced with the clamour of the city.

The whale died during a rescue attempt on 21 January. The river's banks were brought to a standstill for two days as onlookers jostled to watch the whale's plight.

Dried out

Northern bottlenose whales (Hyperoodon ampullatus) generally feed on squid, diving to more than 1,000 metres in search of a meal. An autopsy of the whale revealed some squid beaks in its stomach, but Jepson says it is unlikely to have eaten during the three days or so when it was lost.

"The ultimate cause of death is believed to be the result of a combination of factors, including severe dehydration, some muscle damage and reduction of kidney function," he says.

The preliminary findings show no indication that the whale was thrown off course by loud noises from military sonar or other human activity, Jepson adds. Conservationists have argued that previous strandings involving a range of whale and dolphin species have been due to the disorienting effects of military sonar. The issue has been the subject of several court cases over the past few years, and some campaigners are concerned that a US research committee set up to address the problem has just disbanded (see " Panel quits in row over sonar damage").

However, strandings due to sonar generally involve several whales being washed up along coastlines at roughly the same time, and mostly affect other species, such as beaked whales.

Textbook rescue

The team denies that the rescue attempt, which involved hauling the whale on to a barge and taking it downriver to nearby Gravesend, unnecessarily jeopardized the whale's health. "I think the medical team worked wonderfully well," said Mark Stevens of British Divers Marine Life Rescue, which coordinated the effort. "It was textbook... and we have actually written a textbook on these sort of rescues."

The whale is one of only a few dozen stranded on Britain's coastline in the past two centuries. The species is not threatened, but strandings are nevertheless valuable opportunities to study the creatures and attract concern for their welfare. "Hopefully this highlights the need and desire to conserve whale species in general," Jepson says.

The entire skeleton has now been delivered to London's Natural History Museum, where samples will be stored for researchers, says Richard Sabin, the museum's mammal curator. The autopsy will conclude within two weeks.

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