The latest young whale to have died beached in the Humber Estuary, around 800m from the shoreline.
Experts remain baffled as the creature, along with others, was probably of a species rarely found stranded on the British coast.
The 33ft (10m) animal was trapped in shallow water near the East Yorkshire village of Skeffling, on the north bank of the River Humber.
Conservationists examining the animal say they are 95% certain it is a female Sei whale.
Andy Gibson, of the Yorkshire Wildlife Trust, said Sei whale strandings were very rare.