- Researchers say the ocean's top predators
have been forced to change their diet as a direct result of human-induced
- Killer whales in seas off the coast of
Alaska are reported to be eating the world's smallest sea mammal, the sea
otter, which they previously tended to ignore.
- Writing in the journal, Science, the
researchers say this is because their usual prey, sea lions and harbour
seals, are dying out through over-fishing and altered fish migration patterns
caused by global warming.
- The researchers say the effect on sea
otters is devastating: one killer whale can eat nearly 2,000 of them in
- The population of sea otters through
large areas of western Alaska has dropped by about 25% a year since the
phenomenon was first noticed in 1991, according to the report.
- Threat to ecosystem
- The killer whales' new eating habits
are beginning to have a deeper - and potentially more dangerous impact
on the environment - as their effects begin taking their toll on other
levels of the food chain.
- James Estes, a marine ecologist at the
University of California, Santa Cruz, who led the study said: "A whole
number of species are affected by what the sea otters do. Things that are
rare can impact the ecosystem quite a bit."
- Crucially, sea otters control the population
of sea urchin, which strips kelp forests that many marine species need
- With the number of sea otters dwindling,
sea urchins have begun to flourish, in turn causing kelp forests of the
western Alaska coastal ecosystem to disappear.
- "I do think this is a huge conservation
issue," said Mr Estes.
- "The whole concept is to maintain
an ecosystem and that is not being done in this one."
- Killer whales - or orcas - are the largest
member of the dolphin family.