- The bones of beached whales show signs of decompression
sickness - the "bends" suffered by deep-sea divers - which scientists
believe could explain why some sea mammals are stranded en masse.
-
- A study of the skeletons of sperm whales has found that
many of them suffered from a type of bone damage normally associated with
the bends, when bubbles of nitrogen form in the blood causing pain and
distress.
-
- The findings lend support to the theory that loud underwater
noises produced during naval exercises using submarine sonar could startle
whales and dolphins and cause them to surface more rapidly than they would
normally.
-
- For years, marine biologists have believed that sea mammals
are somehow immune to decompression sickness but the latest study, published
in the journal Science, forms part of a growing body of evidence suggesting
this is not the case.
-
- Michael Moore and Greg Early, of the Woods Hole Oceanographic
Institution in Massachusetts, found extensive damage, called osteonecrosis,
to the bones of stranded sperm whales.
-
- They suggest that this could support the idea that sea
mammals in general are vulnerable to becoming stranded when they are startled
into rising too soon from a deep dive.
-
- "The long-held dogma of complete immunity to decompression
sickness in marine mammals should be revisited," the scientists say.
"It therefore appears that sperm whales may be neither anatomically
nor physiologically immune to the effects of deep diving," they say.
-
- Sperm whales can dive more than two miles in the search
for their quarry - giant squid - and any sudden rise to the surface could
in theory cause dissolved nitrogen to come out of solution as gas bubbles.
-
- If these bubbles form in the tissues they can cause acute
pain by pressing against nerves and blocking small blood vessels, resulting
in the muscles being starved of oxygen. When this happens in bone, small
areas of the tissue can die, leading to the formation of tiny cavities.
-
- Moore and Early studied the bones of stranded whales
dating back 111 years and found the sort of cavities associated with the
bends.
-
- What was interesting was that some of the skeletons obviously
predated the use of submarine sonar and seismic explosions for oil exploration.
They suggested therefore that such damage from decompression sickness may
be a normal feature of a sperm whale's life, which the animals try to minimise
by rising slowly to the surface.
-
- Dr Moore said anything that interfered with this evolved
behaviour, such as acoustic signals from a submarine or a seismic explosion
from a ship exploring for oil, could disrupt their carefully evolved slow
ascent.
-
- "If any acoustic stressors were to override normal
behaviour, then they may run the risk of getting acute nitrogen problems
which could cause pain and potentially strand them," Dr Moore said.
-
- "This study opens the question that acoustic stressors
may be impacting the normal physiology of these animals," he said.
-
- Another team of scientists investigating a mass stranding
of beaked whales off the Canaries in 2002 reported last year that all of
the animals showed signs of acute decompression sickness in their soft
tissues.
-
- Paul Jepson, of the Institute of Zoology in London, who
took part in the study, said that discovering signs of decompression sickness
in whales suggested a possible reason why strandings were linked with submarine
exercises.
-
- "It's still a hypothesis. There are pieces of the
jigsaw that are strongly supportive but we don't have everything in the
jigsaw that proves it," Dr Jepson said.
-
- ©2004 Independent Digital (UK) Ltd. All rights reserved
-
- http://news.independent.co.uk/world/science_technology/story.jsp?story=595873
|