[Jordan and Evermann, 1896-1900, p. 866, Scomber colias Gmelin.]
The hardhead (by which name it is commonly known to fishermen) resembles the common mackerel so closely that we need mention only the points of difference. Most important of these, anatomically, is the fact that the hardhead has a well-developed swim bladder connected with the esophagus, which the mackerel lacks. But it is not necessary to open the fish to identify it for there is a characteristic color difference between the two, the mackerel being silvery-sided below the mid line. Whereas the lower part of the sides of the hardhead (otherwise colored somewhat like the mackerel) are mottled with small dusky blotches, and the chub has a larger eye than the mackerel. Less obvious differences are that the dorsal fins are closer together in the chub and that there are only 9 or 10 spines in its first dorsal fin instead of 11 or more, which is the usual count in the mackerel.[page 334]
This is a smaller fish than its better known relative, growing to a length of about 8 to 14 inches only.
Hardheads school like mackerel, and their feeding habits are much the same, for Doctor Kendall found fish on Georges Bank in August 1896, full of the same species of pelagic Crustacea and Sagittae that the mackerel had taken at the same time and place, while specimens taken at Woods Hole had dieted chiefly on copepods, to a less extent on amphipods, Salpae, appendicularians, and young herring. They follow thrown bait as readily and bite quite as greedily as mackerel do. Their breeding habits have not been studied.
Temperate Atlantic Ocean, north to outer Nova Scotia and to the Gulf of St. Lawrence in the west, to England in the east. It is represented in the Pacific by a close ally, Pneumatophorus japonicus. It is a more southerly fish than the mackerel.
Goode, long ago summarized the early history of the chub mackerel in our waters, which briefly was as follows:
It was tremendously abundant during the last of the eighteenth century and early years of the nineteenth, down to 1820-1830. Thus Capt. E. E. Merchant, an experienced and observant fisherman, described them as so plentiful off Provincetown from 1812 to 1820 that three men and a boy could catch 3,000 in a day on hook and line. But it practically disappeared from the United States coast some time between 1810 and 1850. It is interesting to note, as Captain Atwood pointed out, that destructive methods of fishing had nothing to do with the case, for its disappearance antedated the introduction of traps, pounds, or purse seines; it also antedated the reappearance of the bluefish (p. 386); hence cannot be blamed on these sea pirates. So completely did the hardheads vanish that the Smithsonian Institution tried in vain for 10 years prior to 1879 to obtain a single specimen. But a school was taken in the summer of 1879 in a trap at Provincetown (where representatives of the U. S. Fish Commission were stationed at the time), and though none were seen in 1880 there were some off the coast of New York in 1886.
We find no definite record of the status of the hardhead during the next decade. But Bean describes them as abounding off New York in 1896, swimming up little creeks in such numbers that they could be dipped in boat loads. And hardheads were taken singly and in schools by the mackerel fleet on Georges Bank during that same August, while many were caught on hook and line from the Grampus in Block Island Sound during the first week of that September.
Kendall found them at Monomoy, the southerly elbow of Cape Cod in 1898, and they were sufficiently restablished by then for Smith to describe them as uncommon to abundant at Woods Hole. They then dropped out of the published record again (they are not separated from the [page 335] common mackerel in the fishery returns) until 1900, when they were found in the Casco Bay region. There is no reason to suppose that they appeared in any numbers anywhere on our coasts during the period 1900 to 1906, but in the latter year many were taken in the traps near Woods Hole, also in 1908. And the mackerel fleet found great schools of hardheads on Georges Bank in 1909, when vessels brought in fares of 50,000 to 100,000 of them during the first week of July, their small size (500 to 700 to the barrel) suggesting that there had been a great production of hardheads a year or two previous. Fishermen speak of catching a few from time to time since then, but no great numbers. We caught one at Cohasset on the south shore of Massachusetts Bay in September 1942.
In its years of plenty, which fall at long intervals, however, the chub mackerel is likely to appear wherever mackerel do off the Massachusetts coast, especially about Provincetown. Thus 13,420 pounds were taken in traps at North Truro, in 1952, between August 11 and October 5. Other definite Gulf of Maine records are mostly about Casco Bay and one from Johns Bay, Maine. We found no record of it farther east along the coast of Maine; it is unknown in the Bay of Fundy, nor does it seem to reach the west Nova Scotian coast. But in good "hardhead" years, it is to be expected all along Georges Bank and on Browns as well, to judge from its occasional visits to the outer coast of Nova Scotia.
The chub mackerel is as choice a table fish as the mackerel, and no distinction is made between them in the market, other than the size of the individual fish.
 This genus is separated from Scomber by having a well developed swim bladder which the true mackerel lacks (see Starks, Science, N. Ser., vol. 54, 1921, p. 223).
 It is reported from St. Margaret Bay and Halifax by Vladykov (Proc. Nova Scotian Inst. Sci., vol. 19, 1935, p. 7), and Schmitt (Monographie de l'Isle de Anticosti, 1904, p. 285, Paris) credits it with "apparitions irrégulières" at Anticosti.
 Fish. Ind., U. S., Sect. 1, 1884, p. 303.
 Bull. 60, New York State Mus., Zool. 9, 1903, p. 383,
 Field notes supplied by Dr. W. C. Kendall.
 Bull. U. S. Fish. Comm., vol. 17, 1898, p. 95.
 Boston Herald, July 9, 1919.
 Scattergood, Trefethen, and Coffin (Copeia, 1951, No. 4, p. 298), report one caught in August 1949.