Common bonito Sarda sarda (Bloch) 1793

BONITO; SKIPJACK; HORSE MACKEREL

Description—

This bonito is shaped much like a small tuna, being thick and stout bodied, about one-fourth as deep as it is long (not counting the caudal fin), and similarly tapering to a pointed snout and very slender caudal peduncle. It is tuna-like also, in that its body is scaled all over, that its caudal peduncle has median longitudinal keels, and that its two dorsal fins are so close together that they are practically confluent. But the shape of its fins distinguishes it at a glance from a small tuna, the only regular member of the Gulf of Maine fish fauna, with which it is apt to be confused,^[83] its first dorsal being relatively much longer than that of the tuna (about one-third as long as the body, not counting the caudal, and with about 21 spines), and its second dorsal considerably longer than high, whereas the second dorsal is at least as high as it is long in the tuna.

The mouth, too, of the common bonito is relatively larger than that of the tuna, gaping back as far as the hind margin of the eye, and its jaw teeth are larger, with the two to four in the front of the lower jaw noticeably larger than the others. The shape of its first dorsal, with nearly straight upper margin marks it off from the oceanic bonito (p. 335), also from the false albacore (p. 336), in both of which this fin is very deeply concave in outline; the uniform scaliness of its body, also, is diagnostic, as contrasted with them.

We need only note further that its first dorsal fin is triangular, tapering regularly backward, with only slightly concave upper edge; that the margins of the second dorsal and anal fins are deeply concave; that it has 7 or 8 dorsal finlets and 7 anal finlets; that its tail fin is lunate, much broader than long; and that its lateral line is not deeply bowed below the second dorsal, but is only wavy.

Color—

The color of this bonito is so distinctive as to be a ready field mark to its identity, for while it is steely blue above with silvery lower part of the sides and abdomen, like most of the mackerel tribe, the upper part of the sides are barred with 7 to 20 narrow dark bluish bands running obliquely downward and forward across the lateral line. While young its back is transversely barred [page 338] with 10 to 12 dark-blue stripes, but these dark cross-bars usually disappear before maturity.

Size—

This bonito grows to a length of about 3 feet and to a weight of 10 to 12 pounds.

Habits—

The bonito is a strong, swift, predaceous inhabitant of the open sea and like all its tribe travels in schools. When they visit our northern waters they prey upon mackerel, alewives, menhaden, and other smaller fish such as launce and silversides; also upon squid. They are very likely to be noticed, for they jump a great deal when in pursuit of their prey.

Further to the southward the bonito spawns in June; but it is not likely to spawn in the Gulf of Maine, nor does it do so in the northern part of its European range. Presumably its eggs are buoyant like those of other scombroids. Young 5 to 6 inches long have been reported as common off Orient, N. Y., early in September.^[85] But nothing is known of its rate of growth.

General range—

Warmer parts of the Atlantic, including the Mediterranean; north to outer Nova Scotia,^[86] on the American coast and to Scandinavia on the European coast.

Occurrence in the Gulf of Maine—

Cape Ann is the northern limit to the usual occurrence of the bonito within our Gulf. It has been taken occasionally in Casco Bay, while one was recorded from the mouth of the Kennebec River in September 1930 and two more in July 1932.^[87] But we find no definite record of it east of this on the coast of Maine, or in the Bay of Fundy, although the young have been reported from Halifax on the outer coast of Nova Scotia. Its usual limitation to the southern half of the Gulf appears clearly in the location of the commercial catches.

In 1919^[88] for example, pound nets, traps, and other gear, accounted for almost 34,000 pounds in Cape Cod Bay, but only 90 pounds about Cape Ann, while the entire catch landed in the fishing ports of Maine during that year was only half a dozen fish (44 pounds). And there have been so few of them in Maine waters of late that none at all were mentioned in the fisheries statistics for that State of late years.

Bonito have been known to reach Cape Ann in larger numbers in the past, as happened in 1876, when 73 were taken in one August day in a weir near Gloucester. And probably they are far more plentiful every year out at sea in the southern part of the Gulf than these meager returns would suggest, for fishermen often mention schools of them. Capt. Solomon Jacobs reported them as very plentiful, in August 1896, for instance, in the deep water to the northward of Georges Bank. And we have seen schools of large scombroids, (probably bonito) splashing and jumping off Cape Cod more than once in August.

Apparently bonito visit New England shores only in the summer and fall. Thus the earliest catch made by a certain set of pound nets at Provincetown over a period of about 10 years was in July (1915), the latest on October 4 (1919).

The bonito is more regular in its occurrence west and south of the Cape, being common in some years at Woods Hole and especially off Marthas Vineyard, whence about 57,000 pounds were marketed in 1945. And party-boat captains have described Buzzards Bay and the waters around the Vineyard and Nantucket as full of them in some recent summers.

Importance—

The bonito is a good food fish. It readily bites a bait trolled from a moving boat, once one has the lure that it will strike on the particular occasion. A good many are caught in this way off southern New England, and we can assure the reader that a bonito is one of the strongest fish that swims, weight for weight, and one of the swiftest. Bonito are picked up now and then in Cape Cod Bay by anglers trolling for other fish; we heard of two taken in this way off Wellfleet, on August 29, 1950. But they are never abundant enough in the Gulf of Maine to be worth fishing for there with hook and line.