Rescuers attempt to coax the re-floated whale to deeper water
A 26ft (8m) whale that beached on a mudflat off the south coast of England has suffered kidney failure and faces being put down, rescuers said.
The Northern Bottlenose whale became trapped in Langstone Harbour, off Hampshire, on Thursday and beached overnight during low tide.
Rescuers have suspended an attempt to issue a lethal injection because the mammal has swam back out to sea.
The whale will be put down if it beaches again, experts said.
But if it carries on swimming in deeper water, rescuers said it could take up to two days to die naturally.
Earlier, the whale was freed from mudflats using a special lifting pontoon but it has remained in shallow water.
It may originally have been part of a pod, a larger group, and it's become separated for reasons unknown
Rescuer The British Divers Marine Life Rescue
Experts from the British Divers Marine Life Rescue (BDMLR) said however that even if it made it back out to sea there was no chance of it surviving, because of the renal failure, which was confirmed through blood tests.
The tide has begun to go back out and at some point later, rescuers are hoping the animal will be brought in and given a lethal injection.
Dr Paul Jepson, a vet with the British Zoological Society of London, said: "At some point on the low tide, we'll hopefully be able to get the pontoons on the animal again and bring it towards shore where we can actually administer the lethal injection.
"The lethal injection is just a powerful anaesthetic so it won't be painful to the whale in any way. It should effect euthanasia pretty rapidly."
An operation to try to save the whale began on Thursday but was called off when it became dark. The whale later became beached on a mudflat at 2330 BST.
Rescuers used pontoons to free the whale from mudflats
It is said to be a young adult and was thought to have been about 3,000 miles (4,828 km) off course.
Mystery still surrounds why the whale ended up so far from its normal habitat, but it was possible it was already ill, experts said.
"When it's too shallow to feed, they become dehydrated, and they become weakened and that's the problem," Dr Jepson said.
"Then they strand and get the muscle damage. It's a picture that we're increasingly recognising now, the more we investigate these strandings.
"It may originally have been part of a pod, a larger group, and it's become separated for reasons unknown.
"And it could have been a week or two weeks swimming away from where it should have been, or maybe even more."
During the rescue the whale was placed on a lifting pontoon, from which the creature was able to slip out into the water during a "window of opportunity" between 1030 and 1100 BST at high tide.
Dr Paul Jepson of the London Zoological Society
Stephen Marsh, an advanced marine mammal medic with BDMLR, told BBC News many people had worked to save the whale as well as two specialist vets.
About a dozen firefighters, police, coastguards, the RNLI from Ryde and Hayling Island harbour staff took part in the rescue attempt.
The creature is a deep diving whale and the closest water-depth required is off the Bay of Biscay - about a two-day swim for a whale, Mr Marsh said.
The species feed on deep-sea squid, which are not readily available in the English Channel.
They also get all their water from food, so there had been concern it was not getting fluids and would become dehydrated, Mr Marsh added.
The animal is a young adult, between five and six tonnes in weight, and about 8m (26.2ft) long. Northern Bottlenose whales can grow to more than 9m (30ft).
It is the same species of whale as one that died despite a massive rescue attempt to save it when it swam up the River Thames in January 2006.
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