The haddock is mainly feeding on benthos (bottom-living animals) like bristle worms, mussels and serpent stars, but sandeels and herring eggs are also part of the diet. In the North Sea, the haddock becomes mature at 2-3 years of age, at a length of about 30 cm. A five-year-old haddock is 38-45 cm long. Half a century ago, haddock was abundant in the southern part of the North Sea, but presently most of the haddock are found north of a line from Newcastle to Hanstholm in Denmark.
Haddock is a demersal species found on both sides of the northern Atlantic Ocean. It has a stock structure similar to the cod, except that it does not occur in the Baltic Sea.