A rare Sowerby’s beaked whale washed up on a Lowestoft beach after getting into difficulty “out-of-habitat” in shallower water, a post-mortem suggests.

The whale was discovered on North Beach on Saturday morning, days after a pair of the rarely sighted whales were spotted around the Norfolk coast.

Hours earlier, a Sowerby’s beaked whale was found alive on the beach at Caister, before being successfully returned to the sea.

Rob Deaville, of the Zoological Society of London’s UK Cetacean Strandings Investigation Programme (CSIP), said the female whale was 3.86 metres long and believed to be a juvenile.

Along with a colleague from the Defra-funded CSIP, Mr Deaville carried out an autopsy on the whale on Saturday evening after arriving in the town.

Announcing the findings on Twitter, he said: “Good muscle and blubber mass but no evidence of recent feeding.

“No ingested marine debris, no trauma or significant evidence of disease from gross examination. Case now pending follow up bacteriology and histopathology.

“Findings so far consistent with out of habitat individual - deep diving species in shallow southern North Sea.

“No further sightings in area of second Sowerby’s beaked whale this one was seen with, but prognosis sadly not positive.”

On Thursday afternoon, a family fishing from a boat off Brancaster reported seeing what they believed to be Sowerby’s beaked whales, before reports the following day that a pair of whales had been seen off Blakeney.

Taking to Facebook, a spokesperson for HM Coastguard Lowestoft said: “Humber Coastguard Operations Centre called station officer Claire Hall at home on Saturday morning to investigate reports of either a dolphin or a whale washed up on the beach near Corton.

“The evening before there had been a live stranding of a Sowerby’s beaked whale that was successfully returned to the sea at Caister.

“On arrival at the scene, the station officer asked for the team to be paged following the discovery that it was a deceased whale on the beach and it was likely to have been the same whale from the previous evening.

“Sowerby’s beaked whales are not native to the North Sea and normally reside north of Scotland and west of Ireland.

“They are deep divers and feed on squid and jellyfish found in very deep waters.

“The sea in these parts are not deep enough for this species of whale to successfully feed.

“There have been a few whales of this type wash up in recent weeks and, in light of that, zoologists from London made their way to Lowestoft to investigate.

“This resulted in a post-mortem examination of the mammal on the beach last evening.

“There have been sightings in recent days of a pair of whales. This whale is likely one of that pair.

“We urge you to report any findings of this nature to the coastguard by dialling 999.

“Please keep away from marine life stranded on beaches.

“A sad day for marine life.” Around 1,000 strandings are reported around the country each year, but only around five are Sowerby’s beaked whales.