Shipping threat to endangered whale

The right whale has been hunted almost to extinction

The behaviour of the world's rarest whale, the North Atlantic right whale, could explain why it is more likely than other species to be struck by ships.

Scientists studying the diving habits of the whale say it is more buoyant than other marine mammals and thus more likely to collide with vessels.

Right whales appear to use their positive buoyancy for more efficient swimming and diving

Douglas Nowacek and colleagues

They hope the work will lead to ways to reduce the risk of ships injuring or killing whales.

The North Atlantic right whale is critically endangered with only about 300 individuals left.

Conservationists estimate that about half of all right whale deaths are caused by collisions with ships.

'Easy target'

The right whale was the earliest whale species to be hunted on a systematic commercial basis. It got its name because it was considered to be the right whale to kill.

Right whale facts

One of the rarest mammals in the world

Hunted since the 11th Century

Calves only in waters on the US south-east coast

Winter habitat of much of the population is unknown

The loss of any individual right whale represents a serious setback to the survival of the species

An easy target for hunters, the whale floats to the surface after death and provides a ready supply of valuable oils and meat. It became a protected species in 1935.

In the latest study, scientists at Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, US, attached recording devices to the marine mammals to monitor their behaviour.

They found that the right whale possesses an unusual characteristic not found in other species. Right whales are naturally buoyant, which affects how they swim and dive.

The whales have to put a lot of swimming effort into diving down into the ocean but can glide quickly upwards. Many marine mammals have the opposite characteristic: they tend to sink, so can move downwards more quickly than upwards.

'Added risks'

The upward, or positive, buoyancy of the right whale means it has more difficulty in diving to escape from dangers on the surface such as an approaching ship.

The authors write in the journal of the UK Royal Society: "Right whales appear to use their positive buoyancy for more efficient swimming and diving.

"However, this buoyancy may pose added risks of vessel collision.

"Such collisions are the primary source of anthropogenic mortality for North Atlantic right whales, whose population is critically endangered and declining."