MACKEREL. Mackerels are pelagic fishes, belonging to a small family, Scombridae, of which the tunny, bonito. albacore, sucking-fish (Echeneis), and a few other tropical genera are members (see ICHTHYOLOGY, vol. xii. p. 690). Although the species are fewer in number than in the majority of other families of fishes, they are, widely spread and extremely abundant, peopling by countless schools the oceans of the tropical and temperate zones, and approaching the coasts only accidentally, occasionally, or periodically. The mackerels proper (genus Scomber) are readily recog-nized by their elegantly shaped, well-proportioned body, shining in iridescent colours. Small, thin, deciduous scales equally cover nearly the entire body. The dorsal fin extends over a great part of the back, and consists of several portions : the anterior, composed of feeble spines which can be laid backwards in a groove ; the posterior, of rays only, of which the five or six hindmost are detached, forming isolated " Unlets." The shape of the anal finis similar to that of the rayed dorsal. The caudal fin is cresoent-shaped, strengthened at the base by two short ridges on each side. The mouth is wide, armed above and below with a row of very small, fixed teeth.
No other fish shows finer proportions in the shape of its body. Every " line " of its build is designed and eminently adapted for rapid progression through the water; the muscles massed along the vertebral column are enormously developed, especially on the back and the sides of the tail, and impart to the body a certain rigidity which interferes with abruptly sideward motions of the fish. Therefore mackerel generally swim in a straightforward direction, deviating sidewards only when compelled, and rarely turn-ing about in the same spot. They are in almost continuous motion, their power of endurance being equal to the rapidity of their motions. Mackerel, like all fishes of this family (with the exception, perhaps, of Echeneis, which has not yet been examined in this respect), have a firm flesh; that is, the muscles of the several segments are interlaced, and receive a greater supply of blood-vessels and nerves than in other fishes. Therefore the flesh, especially of the larger kinds, is of a red colour; and the energy of their muscular action causes the temperature of their blood to be several degrees higher than in other fishes.
All fishes of the mackerel family are strictly carnivorous ; they unceasingly pursue their prey, which consists princi-pally of other fish and pelagic crustaceans. The fry of clupeoids, which likewise swim in schools, are followed, by the mackerel until they reach some shallow part of the coast, which their enemies dare pot enter.
Mackerels are found in almost all tropical and temperate seas, with the exception of the Atlantic shores of temperate South America, where they have not hitherto been met with. The distinctive characters of the various species have not yet been fully investigated; and there is much confusion in the discrimination of the species. So much is certain that the European mackerel are of two kinds, of which one, the common mackerel, Scomber scomber, lacks, while the other possesses, an air-bladder. The best-known species of the latter kind is Scomber colias, the " Spanish " mackerel; a third, Scomber pneumaiophorus, is believed by some ichthyo-logists to be identical with S. colias. Be this as it may, we have strong evidence that the Mediterranean is inhabited by other species different from S. scomber and S. colias, and well characterized by their dentition and coloration. Also the species from St Helena is distinct, Of extra-Atlantic species the mackerel of the Japanese seas are the most nearly allied to the European, those of New Zealand and Australia, and still more those of the Indian Ocean, differing in many conspicuous points. Two of these species occur in the British seas : Scomber scomber, which is the most common there as well as in other parts of the North Atlantic, crossing the ocean to America, where it abounds; and the Spanish mackerel, Scomber colias, which is distinguished by a somewhat different pattern of coloration, the transverse black bands of the common mackerel being in this species narrower, more irregular or partly broken up into spots, while the scales of the pectoral region are larger, and the snout is longer and more pointed. The Spanish mackerel is, as the name implies, a native of the seas of southern Europe, but single individuals or small schools reach fre-quently the shores of Great Britain and of the United States.
The home of the common mackerel (to which the following re-marks refer) is the North Atlantic, from the Canary Islands to the Orkneys, and from the Mediterranean and the Black Sea and the coasts of Norway to the United States.
Towards the spring large schools approach the coasts. Two causes have been assigned of this migration : first, the instinct of finding a suitable locality for propagating their species ; and, secondly, the search and pursuit of food, which in the warmer season is more abundant in the neighbourhood of land than in the open sea. It is probable that the latter is the true and only cause, for the following reasons:—mackerel are known to increase much more rapidly in size while in the neighbourhood of land than in the months during which they lead a roving pelagic life in the open sea ; and, further, one-year and two-year-old fishes, which have not yet attained maturity, and therefore do not travel land-wards for the purpose of spawning, actually take the lead in the migration, and are followed later on by the older and mature fishes. Finally, according to the observations made by Sars, vicinity of land or shallow water are not necessary conditions for the ovipo-sition of mackerel ; they spawn at the spot which they happen to have reached during their wanderings at the time when the ova have attained their full development, independently of the distance of the land or of the depth of water below them, as the ova float and the embryo is developed on the surface of the water.
In the month of February, or in some years as early as the end of January, the first large schools appear at the entrance of the English Channel, and are met by the more adventurous of the drift-net fishers many miles west of the Seilly Islands. These early schools, which, as we mentioned above, consist chiefly of one-year and two-year-old fishes, yield sometimes enormous catches, whilst in other years they escape the drift-nets altogether, passing them, for some hitherto unexplained reason, at a greater depth than that to which the nets reach, viz., 20 feet. As the season advances, the schools penetrate farther northwards into St George's Channel or eastwards into the English Channel. The fishery then assumes proportions which render it next in importance to the herring and cod fisheries. In Plymouth alone a fleet of some two hundred boats assembles ; and on the French side of the Channel no less capital and labour are invested in it, the vessels employed being, though less in number, larger in size than on the English side. Simultaneously with the drift-net the deep-sea-seine and shore-seine are used, which towards June almost entirely supersede the drift-net. Towards the end of May the old fish become heavy with spawn, and are in the highest condition for the table ; and the latter half of June or be-ginning of July may be regarded as the time at wdiieh the greater part of mackerel spawn.
Mackerel are scarcely less abundant in the German Ocean ; prob-ably some of the schools never leave it, and this resident stock (if we are allowed to apply this term to a fish which is ever shifting its quarters) is increased by the schools coming from the Atlantic through the English Channel or round the north coast of Scotland. The schools approach the coasts of the German Ocean somewhat later in the season, partly owing to the greater severity of the weather, which detains the resident fishes in the open sea, and partly owing to the greater distance which the Atlantic shoals have to travel. On the Norwegian coast mackerel fishing does not begin before May, whilst on the English coasts large catches are frequently made in March. Large cargoes are now annually im-ported in ice from Norway to the English market.
After the spawning the schools break up into smaller companies which are much scattered, and offer for two or three months employment to the hand-line fishermen. They now begin to dis-appear from the coasts and return to the open sea. Single indi-viduals or small companies are found, however, on the coast all the year round ; they may have become detached from the main bodies, and be seeking for the larger schools which have long left on their return migration.
Although, on the whole, the course and time of the annual migration of mackerel are marked with great regularity, their appearance and abundance at certain localities are subject to great variations. They may pass a spot at such a depth as to evade the nets, and reappear at the surface some days after farther eastwards; they may deviate from their direct lino of migration, and even temporarily return westwards. In some years between 1852 and 1867 the old mackerel disappeared off Guernsey from the surface, and were accidentally discovered feeding at the bottom. Many were taken at 10 fathoms and deeper with the line, and all were of exceptionally large size, several measuring 18 inches, and weigh-ing nearly 3 lb ; these are the largest mackerel on record.
The mackerel most esteemed as food is the common species, and individuals from 10 to 12 inches in length are considered the best flavoured. In more southern latitudes, however, this species seems to deteriorate, specimens from the coast of Portugal, and from the Mediterranean and Black Sea, being stated to be dry and resembling in flavour the Spanish mackerel (S. colias), which is not esteemed for the table. See also FISHERIES. (A. C. G.)
The above article was written by A. Günther, M.D., F.R.S.