The videotape recording came as a North Sea oil industry submarine carried out a seabed survey 100 miles east of Aberdeen and provided almost unprecedented visual evidence of a phenomenon which has long mystified zoologists.
The guillemot's dive was almost modest compared to previous achievements of members of the auk family - the very similar Arctic-based Brunnich's guillemots have been reported to dive as deep as 630ft.
But what experts do not yet know is how these comparatively small creatures - an adult guillemot is just about barely 16in long - have evolved the ability to pull off diving feats which humans can only equal with sophisticated equipment.
The bird was seen swimming in the appropriately named Guillemot Field which is being developed by Shell UK. A survey official, Doug McCall, said: "It was swimming about like a fish, perfectly happily, which to us was phenomenal when you consider the pressure at that depth."
The cameras later picked up what may have been another guillemot flashing by.Reuse content