The female yearling hauled itself ashore near the Sea Scout shed on Portobello Rd.
Department of Conservation coastal ranger Jim Fyfe said the seal's visit to the mainland was ''not very common at all''.
''It is certainly pretty cool.
''I can count on one hand the number of times I have seen one in 15 years.''
The seal was moulting, which may have been why it came ashore, he said.
It was not spotted yesterday.