Long-spined Sea-scorpion Taurulus bubalis

Also known as Long-spined Bullhead.

Fish are very far indeed from my area of expertise and I had no idea what this was. My first stab at the ID was wrong, but James Spencer suggested that it looked like this species, and I agree. The Black Guillemot probably didn't care what it was called.

Long-spined Sea-scorpion (held by Black Guillemot), Scrabster Harbour (Highland, UK), 12th February 2024