The bearded seal, a rare sight this far south, was spotted by taxi driver Ertie Burgess on the old Bressay slip below the Market Cross.
A Facebook post by Mr Burgess generated a great deal of interest and a number of people turned out at Victoria Pier hoping to see the animal.
One commenter suggested this was only the third sighting of a bearded seal in Shetland.
The animal is normally found in the Arctic and sub-arctic waters around places such as Greenland, Northern Russia, Alaska and Northern Canada.
Earlier this year a bearded seal was spotted on the Isle of Harris.