Haddock Melanogrammus aeglefinus; Linnaeus, 1758. Family: Gadidae
The haddock, of which it is said that the large dark mark above the pectoral fin is a finger print of St Peter the biblical fisherman, is widely distributed in the North Atlantic. It occurs in all areas around the Scottish coasts and can be found as far south as the Humber estuary. Haddock are usually found in depths less than 200 metres. Results from tagging experiments suggest that there may also be links between the stocks of North Sea haddock and those to the northwest of Scotland.
Growth rates of haddock may differ by area or by sex with female haddock generally growing faster than the males. At two years old only one fifth of female haddock can spawn while more than half can spawn at three years old. By the time they reach four years old, most fish are mature. During the season an individual female of around 40 cm is able to produce around 300,000 eggs which are released in a number of batches over a long period of time. Spawning runs from March until May and occurs in almost any area around the Scottish coasts to the Norwegian Deeps. It takes from one to three weeks for the pelagic eggs to hatch.
There are differences in the length of the spawning season, associated with the size and age of the local population. The spawning stock on inshore grounds usually consists of smaller and younger fish than those found in offshore areas. The length of the spawning period of these young fish is less than half that of the larger and older fish found offshore. Most of the newly hatched larvae do not travel far from the spawning grounds but some from the west coast spawning grounds can be transported into the North Sea, entering through the Fair Isle/Shetland Gap or to the northeast of Shetland. Young haddock spend the first few months of life in the upper water layers before adopting the demersal way of life. After spawning, the adult shoals spread out over a much wider area but as the year proceeds some haddock tend to concentrate in specific areas to feed.
The diet of haddock varies with the size of the fish, the time of year, and with the area. In the winter months haddock of all sizes feed mainly on worms, small molluscs, sea urchins and brittle stars. In the spring and summer fish prey, especially sandeels are important, particularly for the larger haddock. In the more northerly areas Norway pout is the most common fish eaten. Haddock also feed heavily on the demersal egg deposits of herring.