Mackerel is a fast swimming species belonging to a group of fish known as the scombrid family, which are related to the tuna. They are found in brackish marine waters in depths of up to 1000 m (though more normally in depths of 0-200 m). Abundant in cold and temperate shelf areas, they form large schools near the surface. They overwinter in deeper waters but move closer to shore in spring when water temperatures range between 11 degrees and 14 degrees C. Mainly diurnal, they feed on zooplankton and small fish. Mackerel are batch spawners, they spawn mainly in March to July; the eggs and larvae are pelagic. After spawning, the adults feed very actively, moving around in small shoals. By 3 years old, most mackerel are mature (at a length of approximately 28 cm). Females shed their eggs in about twenty separate batches over the course of the spawning season. Juvenile mackerel grow quickly and can reach 22 cm after one year, and 30cm after 2 years. Mackerel can attain a maximum length of about 70 cm and weight of 3.4 kg. They may live for more than 20 years.