The Atlantic Mackerel is by far the commonest of the 10 species of the family that have been caught in British waters. It is extremely common in huge shoals migrating towards the coast to feed on small fish and prawns during the summer. Overfishing has reduced the numbers in parts of the North Sea.

Mackerel are found off all British coasts, in the Mediterranean Sea, and on the American side of the north Atlantic.

Two distinct stocks have been identified in British waters, one spawning in the North Sea, and the other spawning to the west of the British Isles.

Healthy fish are coloured an iridescent blue-green on the back, with curved black lines. Lengths of up to 66 cm (26 in) have been recorded, but 40 cm (16 in) is more usual. Fish over 680 g (1 lb 8 oz) are considered large.

When freshly caught, the mackerel makes excellent eating, but the flesh deteriorates rapidly. A similar species, the Spanish Mackerel, Scomber japonicus, is found in the English Channel during the summer. Both species are distinguished by five small finlets between the second dorsal and tail fin, and a further five finlets between the anal fin and the tail.

At spawning time, the eggs and sperm of the mackerel are released into the sea. Mackerel can release up to one million eggs.  The egg is just over 1 mm long, with an amber oil globule that keeps it floating in the pelagic surface waters. Surviving larvae at 3 mm long will feed on copepods. By the first autumn, the North Sea population of Mackerel will attain a length of 15 cm, reaching 25 cm after one year.

Stomach content analysis of adult mackerel sampled in Loch Ewe and the Minch (Scottish seas) during the summer months indicates a variety of prey including small fish such as sand-eels, Ammodytes spp., small gadoids (cod family), and clupeoids (herrings), as well as filter feeding for small crustaceans such as Euphausids.

Small creatures exceeding 1.5 mm can be sieved from the water in close-set gill-rakers. This can occur when the fish swims at speeds in excess of 0.7 body lengths per second. Gill ventilation (breathing) occurs by a method known as "ram ventilation" and the cessation of the normal buccal/opercular pump system. Its speed may reach 25-30 body lengths per second.

In Sussex waters, mackerel are known to feed on juvenile prawns of the species Palaemon serratus, about 10 mm long, in large numbers.

Feeding ceases when the mackerel return to deeper water during the winter.

Mackerel are long-lived fish, if they are not caughty, and fish of over 25 years old have been caught in the North Sea.

The largest Atlantic Mackerel ever caught on rod and line was from deep water off the western Swedish coast (Svaberget) and weighed 3.074 kg (6 lb 13 oz), (1995).
 

Text by Andy Horton. Photographs by T.G. Mc. Innes (Aberdeen)