Found a dozen similar dead fish on the beach as the tide went out. I only searched a few hundred metres of shoreline looking for them, there may have been more.
An hour earlier there had been large numbers of gulls, shags, terns and other seabirds feeding over a range of 20 to 100 metres from shore, not sure whether the two events are related.
Gulls were finishing off the fish remains, a couple were still in the surf.
Not sure whether all the fish were the same species, but will post 3 separate observations, let me know if some should be split into more observations. AA battery for scale on first photo.(first photo separated out to another observation)

See also 1130154, 1130153, 3750457