Diet of mackerel (Scomber scombrus) larvae at the shelf-edge to the south-west of the British Isles and the incidence of piscivory and coprophagy

The gut contents of mackerel larvae (2.1-9.2 mm in length) were examined fr om samples taken in the spring and early summer over the shelf-edge to the south-west of the British Isles. Larvae < 5.9 mm in length fed mainly on un identified phytoplankton material, copepod eggs and copepod nauplii. In the diet of larvae > 6 mm in length, the proportion of copepodite stages of co pepods increased, while the proportion of copepod nauplii remained relative ly constant. A limited amount of coprophagous feeding on crustacean faecal pellets was observed in larvae > 3 mm in length (0.2-22.1% of gut contents by weight). Piscivorous feeding occurred in larvae in the length range 4-7. 9 mm and, although fish larvae were not numerous in the diet (0.3-4.6 % num erically), they accounted for a significant proportion of the diet by weigh t (56.1-72.1 %). Larvae developed teeth from 3.1 mm in length; by 5 mm all larvae had teeth, a feature which may facilitate their piscivorous feeding. There was a higher incidence of feeding during daylight hours, although at least 55 % of larvae sampled at night still had food items in their gut co ntents.