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Table of Contents

The mackerels are a very homogeneous group, all of them agreeing in having a spiny dorsal as well as a soft dorsal fin, several small finlets behind the latter and behind the anal, a very slender caudal peduncle, a deeply forked or lunate caudal fin, a very shapely form tapering both to snout and to tail, and velvety skin with very small scales. All, too, are predaceous, swift swimmers, and powerfully muscled, while all are fish of the open sea and more or less migratory.

In the following key we mention all species so far actually recorded from within the limits of the Gulf of Maine, but it would not be astonishing if still others were to stray in from the open Atlantic from time to time.[92]

1. The two dorsal fins are separated by a space at least as long as the length of the first dorsal 2  
The two dorsal fins adjoin each other or are separated by a space much shorter than the length of the first dorsal 3  
2. The sides below the mid line are silvery, not spotted Mackerel, p. 188, 317
The sides below the mid line are mottled with dusky blotches Chub Mackerel, p. 209, 333
3. Body scaleless, except along the lateral line and in the region of the shoulders (the so-called "corselet") 4  
Entire body covered with scales 5  
4. The lower part of the sides, below the lateral line, is marked with dark longitudinal bands, but there are no definite dark markings on the back Striped Bonito, p. 335
There are no dark markings on the lower side below the lateral line, but the back has dark markings False Albacore, p. 336
5. The anal fin is about twice as high as long; the corselet of large scales is obvious Tuna, p. 338
The anal fin only is about as high as long; there is no corselet of large scales 6  
6. Second dorsal fin noticeably lower than the first dorsal Common Bonito, p. 337
Second dorsal fin at least as high as first dorsal 7  
7. Lateral line with an abrupt downward curve under second dorsal fin Cavalla, p. 349
Lateral line descending gradually 8  
8. Sides with a few rows of oval bronze or yellowish spots and with one or two longitudinal dark streaks King Mackerel, p. 348
Sides with bronze spots but without longitudinal dark streaks Spanish Mackerel, p. 347

[93] The long finned Albacore (Thunnus alalunga Bormaterre, 1788) has been taken at Woods Hole, also on Banquereau Bank, off eastern Nova Scotia (Goode and Bean, Bull. Essex Inst., vol. XI, 1879, p. 15), so is likely to show up in the Gulf of Maine sooner or later. It is made easily recognizable among North Atlantic mackerel fishes by its very long pectoral fins which reach back past its second dorsal fin.

[92] Fraser-Brunner, Ann. Mag. Nat. Hist. Ser. 12, vol. 3, No. 26, 1950, pp. 131-163, has recently given a synopsis of the mackerels, with useful keys and excellent illustrations for all known species. We follow him in uniting them all in the old and inclusive family Scombridae rather than Jordan, Evermann and Clark (Rept. U. S. Comm. Fish. (1928) Pt. 2, 1930) who have distributed them among four families, Cybiidae, Katsuwonidae, Scombridae, and Thunnidae.