FISHES OF THE GULF OF MAINE 



319 



But the iridescent colors fade so rapidly after 

 death that a dead fish gives little idea of the bril- 

 liance of a living one. 



Size. — Most of the grown fish are between 14 

 and 18 inches long; a few reach a length close to 22 

 inches. Fourteen-inch fish weigh about 1 pound 

 in the spring and about 1 }{ pounds in the fall when 

 they are fat; 18-inch fish weigh about 2 to 2% 

 pounds; a 22-inch mackerel will likely weigh 4 

 pounds. An unusually large mackerel is taken 

 occasionally; in 1925, for example, the schooner 

 Henrietta brought in one weighing 7% pounds. 



Habits. — Mackerel are a swift-moving fish, 

 swimming with very short sidewise movements of 

 the rear part of the body and of the powerful 

 caudal fin. When caught they beat a rapid tattoo 

 with their tails on the bottom of the boat until 

 exhausted. And they require so much oxygen for 

 their vital processes that when the water is warm 

 (hence its oxygen content low) they must keep 

 swimming constantly, to bring sufficient flow of 

 water to their gill filaments, or else they die. 95 



Despite their great activity, they do not leap 

 above the surface, as various others of their tribe 

 do, unless perhaps to escape some larger fish. 



The mackerel, like the herring, has the habit of 

 gathering in dense schools of many thousands. It 

 is not known how long these schools hold together; 

 it would be especially interesting to know whether 

 they do so through the winter when our mackerel 

 are in deep water, but the general opinion of fish- 

 ermen is that they do so throughout the migra- 

 tions at least. Although the mackerel may scatter 

 and the schools mix more or less, especially when 

 they are feeding on the larger and more active 

 members of the free-floating fauna as is said to 

 happen in British waters, the members of any 

 given school usually are all of about the same size, 

 i. e., of the same age. Fish of the year almost 

 always school separately from the others as 

 Sette " has pointed out; he has also pointed out 

 that this tendency of the fish to separate according 

 to size is probably due to the fact that the larger 

 ones swim faster than the smaller ones. 



Mackerel school by themselves, as a rule. But 

 sometimes they are found mingled with herring, 

 alewives, or shad, as Kendall 97 described. We 



" This interesting fact seems first to have been reported by Hall (Amer. 

 Jour. Physiol., vol. 93, 1930, pp. 417-421), and we have observed the same thing 

 In the aquaria at the Woods Hole Oeeanographic Institution. 



» Fish. Bull. U. S. Fish and Wildlife Service, vol. 51, Bull. 49, 1950, p. 264. 



" Bull. TJ. 8. Bur. Fish., vol. 28, 1910, Pt. I, p. 287. 



have yet to learn how mackerel schools hold to- 

 gether, whether by sight or by some other sense. 

 And various explanations have been proposed to 

 account for the schooling habit, such as that it is 

 advantageous for feeding, that it is a concomitant 

 of spawning (this would not explain its persistence 

 out of the spawning season, however, or the fact 

 that any given school is apt to contain green, and 

 spent as well as ripe fish even at spawning time), 

 or that it affords protection from enemies. But 

 when all is said, the instinct prompting it remains 

 a mystery. At any rate, schooling is not a neces- 

 sity, though usual. When mackerel are at all 

 plentiful, and even when they are not, numbers of 

 single wandering fish are often hooked by persons 

 trolling for them, and by flounder and cunner 

 fishermen. 



Schools of mackerel are often seen at the surface. 

 In the daytime they can be recognized by the 

 appearance of the ripple they make, for this is 

 less compact than that made either by herring 

 or by menhaden. Neither do mackerel ordinarily 

 "fin" or raise their noses above the surface, 

 as is the common habit of the menhaden (p. 

 114). An observer at masthead height can per- 

 haps see a school of mackerel as deep as 8 to 10 

 fathoms by day, if the water is calm, and the sun 

 behind him. On dark nights the schools are 

 likely to be betrayed by the "firing" of the water, 

 caused by the luminescence of the tiny organisms 

 that they disturb in their progress. Sette " 

 reports one case of a school recognized by its 

 firing as deep as 25 fathoms; but the water is 

 seldom (if ever) clear enough in the Gulf of Maine 

 for a submerged light to be visible from above, 

 more than 15 fathoms down. 99 The trail of bluish 

 light left behind by individual fish as they dart 

 to one side or the other, while one rows or sails 

 through a school on a moonless, overcast night 

 when the water is firing, is the most beautiful 

 spectacle that our coastal waters afford, and one 

 with which every mackerel fisherman is familiar. 



No one knows how greatly the movements of 

 the mackerel, from day to day, result from invol- 

 untary drifting with the circulatory movements of 

 the water, which are different at different depths, 

 and how greatly they depend on the directive 

 swimming of the mackerel themselves. Our only 



« Fish. Bull. U. 8. Fish and Wildlife Service, vol. 51, Bull. 49, 1950, p. 267. 

 » For observations on the visual transparency of the water of our Gulf, see 

 Bigelow, Bull. U. S. Bur. Fish., vol. 40, Pt. 2, 1927, p. 822. 



