The unusual catch here is an Atlantic horse mackerel, Trachurus trachurus. According to the internet, the species occurs in the northeast Atlantic, Mediterranean and as far down as West Africa in large schools which shoal over sandy bottoms at depths of between 100 and 200 metres. One site suggests it sometimes associates with herrings, a fish which, these days, is rarely caught off these coasts.
Horse mackerel may be common in deeper waters, but this is the first one people have seen here. It was caught off Johnny Watson's boat whilst they were fishing off Glas Eilean. Many thanks to Hughie and Sharon MacLachlan for forwarding Dyane Young's picture. The fish was caught by family friend Tony.