All mackerels are carnivores. Smaller species prefer to eat prawns and krill which are kinds of shrimp. Small mackerels are Atlantic mackerel, chub mackerel, blue mackerel and so on. Small ones also eat small fish like sardines and herring. Larger mackerel prefer to eat larger fish sometimes each other! Those larger mackerels are the Spanish mackerel, king mackerel, and wahoo.