Police believe the man's head had been in the water for at least a couple of years and could have been in the sea for decades.

It was found in the catch of a trawler which was fishing off Hartlepool on February 14, 2008.

Officers from North Yorkshire Police have turned to a forensic anthropologist who has helped them produce a digital reconstruction of how the man may have looked.

They said he would have had an "asymmetric" face because one of his front teeth was missing.

Inspector Tony Quinn said: "Forensic tests lead us to believe that the skull belongs to a man who died between the age of 20 and 50 and had been in the water for a minimum of two to three years, but could, if enclosed in a confined space, have been in the water for a number of decades."

Mr Quinn said the man was thought to have been from north-west Europe. Experts have decided a missing left front tooth was lost before he died.
This could have been due to trauma or a congenital absence of the tooth, he said.

Unless corrected by a dental procedure, the missing tooth would have made the man's face look asymmetric, Insp Quinn added.

He urged anyone who thinks the man could be their relative to contact police so that tests could be arranged which may help.