-- QL 626 L"brary I MPO - Bibliothèque t1 1 U5313 no.17 \\\\\ \\\\\ \\\\\ \\\\\ \\\\\ \\\\\ \\\\\ \\\\ \\\\ c.2 12064603 - Atlantic Mackerel 2 he Atlantic mackerel (Scomber Distribution and migration T scombrus) is a handsome fish - Atlantic mackerel are found over the THE ATLANTIC streamlined and fast swimming, with continental shelf on bath sides of the dark tiger-like striping on its blue and Atlantic Ocean. The European race MACKEREL silvery body. extends from Norway to Spain, as well A member of the family Scom- as into the Mediterranean and Black bridae*, mackerel have a fatty flesh seas. In the northwest Atlantic, with a delicious flavour and are a mackerel range from North Carolina favourite of some Europeans, espe- to Labrador. cially the Portugese, who have fished Atlantic mackerel in the northwest them for centuries. Atlantic comprise two populations: Despite these favourable qualities the southern contingent spawning and a good reputation on European between Cape May and Long Island in tables, consumer demand is relatively April and May and the northern con- low in Canada. Many domestic cus- tingent whose main spawning area is tomers do not know what they are the southern Gulf of St. Lawrence in missing. June and July. Most of the Canadian The majority of the Scombridae are catch is taken from the northern of tropical origin, but the Atlantic population, although some schools mackerel is found in abundance in belonging to the southern population northern waters of the Atlantic. may appear on the Scotian Shelf in the Another member of the family, the summer. Canadian fishermen have Atlantic chub mackerel, only occasion- never fished mackerel intensively ally ventures as far north as the Mari- because of the lack of markets. With time Provinces. extension of jurisdiction and the disap- pearance of foreign fishing, the mack- Description erel stocks are now rebuilding and are The Atlantic mackerel is shaped for being lightly exploited. Recent analyses swimming swiftly with a minimum of indicate catches of up to 150,000 effort. lts body is slender, tapering at metric tons could be safely harvested. the tail and snout. The pectoral fins, Mackerel prefer a water temperature found just behind the gill openings, are between 9° and 12°C, and migrate extended like hydrofoils during slow annually, probably in response to swimming; at high speéds, they are seasonal changes in water temperature swept back and completely pressed to in the northwest Atlantic. The main the body. The pelvic fins, located just known overwintering area is the con- below the pectorals, are extended only tinental shelf south and southwest of during turning. Georges Bank, at depths of 70 to The small scales of the Atlantic 210 m. ln the spring, the more local mackerel give the skin a velvety southern population moves inshore texture. As in many fish, the body is towards the American coast to spawn. countershaded, dark above and light The Canadian or northern con- below. The steel-blue upper surface has tingent migrates northward in spring 23 to 33 dark wavy bands extending from the same over-wintering ground. down to the midline. The lower sides The migration route is not well are silvery with a coppery or brassy iri- understood but it appears that the descence. The belly is silvery-white. contingent moves in a broad band This fish has no swim bladder (often covering most of the Scotian Shelf. called air bladder) and thus it must Sorne large adults arrive inshore along swim continuously to avoid sinking. the Nova Scotia coast in mid-May, on Fig. 1 Atlantic mackerel Most mackerel caught in the com- their way to the main spawning ground mercial fishery are from 25 to 40 cm in the Gulf of St. Lawrence. Immature in length, and weigh between 200 and fish apparently migrate later, and 700 g. many may spend the summer along the Atlantic coast of Nova Scotia. Adults spawning in the Gulf of St. *The large, fast-swimming tunas were previously classified in the same family, but now forma distinct but Lawrence usually remain there or move closely-related family, the Thunnidae. to the areas around Newfoundland 3 (including the east coast) to feed, most likely that females release the before migrating south in October for majority of their eggs at one time, the winter. The timing and the exact rather than releasing a series of smaller destination of these migrations are batches throughout the season. The probably controlled by the duration of fecundity of most spawning females is daylight and the water temperature. In quite high, between 200,000 and years when the water is warmer, mack- 500,000 eggs. erel are abundant off the south and Once released into the water, these east coasts of Newfoundland from eggs suffer an estimated mortality of August to October. 50 per cent per day. Larval mortality is Before the construction of the also very high. The specific causes of causeway across Canso Strait in 1954, egg and larval mortality are not well some mackerel used that route to known. Of course, many groundfish migrate into the Gulf of St. Lawrence. and pelagic fish, including mackerel However, the mackerel population bas and herring, feed on these drifting flourished since then, and this disrup- mackerel eggs and larvae, as well as on tion of part of the migratory path the eggs and larvae of many other apparently bas not affected the total species. lt is also possible that larger stock. larvae may prey upon smaller larvae, especially at high densities. Eggs and Life history larvae are also very sensitive to temp- The northern population of Atlantic erature changes. mackerel contains approximately equal lt is estimated that about 20 per cent numbers of males and females. Sorne of adult mackerel die each year from fish are mature at two years of age at a causes other than fishing. Sudden length of about 30 cm. Most are ma- drops in temperature may kill even ture by four years of age. adult mackerel. Mass mortalities have Eggs are found only in waters over been observed along the northeast MAC KEREL l0°C. In the main spawning area in the coast of Newfoundland in the late fall. southwestern Gulf of St. Lawrence, the Mackerel are preyed upon by large sea greatest numbers are found between animais such as whales, seals, tunas, the Magdalen Islands and the Gaspé and sharks, and also by sea birds, such Peninsula. Spawning takes place in as gannets. Cod and squid also feed CANADA open waters and near the surface in late upon small mackerel. June and early July, with a peak activi- Fishing mortality may take place as ty at about 12°C. The eggs and sperm early as one year of age, depending are released into surface waters and upon the selectivity of the gear used. In must rely on normal water movement recent years, the rate of fishing mortal- and turbulence to bring them in con- ity bas varied greatly. When interna- tact to allow fertilization of the eggs . tional fleets were heavily exploiting the The fertilized eggs then take about over-wintering populations in the early seven days to develop and hatch. lt is '70s, it is estimated that 44 per cent of mackerel four years of age and over were captured each year. ln 1979, with no major international fishery, the rate was about 14 per cent. Fig. 2 General d"stribution of A tlantic Mackerel feed on plankton (small mackerel in the Northwest Atlantic. crustaceans, fish eggs, and larvae) and on small fish (notably capelin, juvenile herring, and mackerel). They engage in both "particulate" feeding (the active pursuit of larger plankton and fish) and "filter" feeding (the gill rakers filter small food items from the water). Heaviest feeding takes place in the spring, when food availability may affect the distribution of fish, espe- cially off Nova Scotia. 4 In the Gulf of St. Lawrence the high Mackerel catches increased dram- summer water temperature and the atically during the late 1960s due to the accompanying high food productivity development of a fishery on the over- permit a rapid first season growth to wintering stocks, carried out by large about 20 cm before the fall migration. freezer and factory trawlers, mostly The total length after one full year is from the USSR, Poland, East Ger- between 22 and 29 cm. Second-year many, and Bulgaria. This fishery was growth is slower, and two-year-olds are rendered possible by the exceptional about 30 cm long by the end of the abundance of the 1959 and 1967 year- year. Few fish survive to 40 cm or classes of young mackerel. Fear of longer, corresponding to an age of at over-fishing prompted the Interna- least 10 years. tional Commission for the Northwest Atlantic Fisheries (ICNAF) to impose The fishery an initial TAC limit in 1973 of Northwest Atlantic mackerel have 450,000 t. The TAC was gradually been harvested since the l 7th century. lowered as scientists gained a better Landings have been extremely vari- understanding of the dynamics of the able. For example, the total catch was stocks. With a TAC of 105,000 t in 8,000 metric tons (t) in 1962, but it had 1977 and 1978, total catches were only risen to 420,000 tin 1973. Catches have 78,000 and 28,000 t respectively. The varied because of changing market low catches in those two years relative conditions, new technological develop- to the TAC are largely due to the in- ments, variations in the abundance of ability of the American fishermen to mackerel and the development of the take their share of the allocations, as foreign offshore fishery.