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A young whale which died after beaching in the Humber Estuary was probably a species rarely seen near the British coast, conservationists have revealed.

Experts examining the 33ft (10m) long animal said they were "95% certain" it was a female sei whale.

The mammal was trapped on the north bank of the River Humber on Friday.

Earlier in September, a Fin whale died after beaching near Immingham. One expert said they would "learn a lot" from the incident.

Another dead whale has also recently been spotted in the mouth of the Humber but has yet to wash ashore.

Specialists from the Yorkshire Wildlife Trust were able to perform a post mortem examination on the whale after it was deposited on salt marsh due to a particularly high tide.

Andy Gibson, from the Trust, said sei whale strandings were very rare.

He said there had only been three strandings of this species in UK waters in the last 20 years.

"It was in shallow water of about 1.2m (4ft) to 1.6m (5.25ft), making contact with the bottom," he said.

"This was about 800m (2,625ft) offshore. When it gets in that situation it rolls onto its side and it can cover its blow hole.

"It is sad but we will be able to learn a lot from it."

The Yorkshire Wildlife Trust said it had noted a rise in whale sightings generally in 2011 but no-one was sure why there might be an increase in the mammals in the North Sea.

Over the summer, a pod of up to 10 minke whales was spotted regularly off the North Yorkshire coast between Whitby and Scarborough.