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FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



contribution in this regard is that we once were 

 able to follow on foot beside a school that was 

 advancing along the Scituate shore at a rate of 

 about 3 to 4 miles an hour, against a tidal current 

 of about one-half knot, until the fish swung 

 offshore and out of our sight. 



The speed at which a school travels when it is 

 not disturbed depends, it seems, on the size of the 

 fish of which it is composed. It has been observed 

 by Sette that mackerel less than one year old 

 swim at about 6 sea miles per hour (10 ft. a second) 

 while circling inside a live car; yearlings at a rate 

 of about 11% sea miles per hour (19 ft. a second), 

 or nearly twice as fast. We find no definite 

 observations on the normal speed of the larger 

 fish, and no one knows how rapidly a mackerel 

 may swim for a short distance, if it is disturbed. 

 Mackerel seen during the warmer months of the 

 year are always swimming, but this rule may not 

 apply in winter, when the water holds more dis- 

 solved oxygen because colder, and when it is 

 probable that their demand upon it is lower. 



The mackerel is a fish of the open sea; while 

 numbers of them, small ones especially, often enter 

 estuaries and harbors in search of food, they never 

 run up into fresh water. Neither are they directly 

 dependent either on the coastline or on the bottom 

 in any way at any stage in their lives. They are 

 often encountered far out over the outer part of 

 the shelf of the continent. But they are most 

 numerous within the inner half of the continental 

 shelf during the fishing season, and their normal 

 range seems not to extend oceanward beyond the 

 upper part of the continental slope, in which they 

 contrast with their relatives the tunas, the bonitos, 

 and the albacores. 



The depth-range of the mackerel is from the 

 surface down to perhaps 100 fathoms at one season 

 or another. (We recur to this in discussing the 

 occurrence of mackerel in the Gulf of Maine, page 

 325.) From spring through summer and well into 

 the autumn, the mackerel are in the upper water 

 layers; shoaler, mostly, than some 25 to 30 fath- 

 oms, and schools of all sizes come to the surface 

 more or less frequently then. But they frequently 

 disappear from the surface, often for considerable 

 periods. And it seems, from fishermen's reports, 

 that the larger sizes tend to swim deeper than the 

 smaller ones, on the whole, especially in mid and 



late summer. 1 It is probable, also, that their 

 vertical movements during the warmer part of the 

 year, when they are feeding actively, are governed 

 chiefly by the level at which food is most abun- 

 dant, which for the most part is shoaler than about 

 50 fathoms, at least on our side of the Atlantic. 



The highest temperature in which mackerel 

 are commonly seen is about 68° F. (20° C). At 

 the opposite extreme they are sometimes found in 

 abundance in water of 46°-47° (8° C); and com- 

 mercial catches are sometimes made in water as 

 cold as 44°-45° (7° C), but odd mackerel only 

 have been taken in temperatures lower than 

 that 2 in American waters. Large catches of 

 mackerel are made, however, by trawlers in the 

 North Sea in winter in water as cold as 43°— 15° 

 (6°-7° C). But as Sette has emphasized, the 

 European mackerel differs racially from the 

 American, and may differ in its temperature rela- 

 tions as well. 



Food. — We may assume that the diet of the 

 young mackerel is at first much the same in the 

 Gulf of Maine as it is in the English Channel, 3 

 namely, copepod larvae and eggs, the smaller 

 adult copepods, various other minute pelagic 

 Crustacea, and small fish larvae. But the young 

 fish depend more and more upon larger prey as 

 they grow. Our Gulf of Maine mackerel have 

 repeatedly been seen packed full of Calanus, the 

 "red feed" or "cayenne" of fishermen, as well as 

 with other copepods (we have examined many in 

 this condition). They also feed greedily, as do 

 herring, on euphausiid shrimps (p. 89), especially 

 in the northeastern part of the Gulf where these 

 crustaceans come to the surface in abundance. 

 Various other planktonic animals also enter regu- 

 larly into the dietary of the mackerel. Thus, 

 Doctor Kendall writes in his field notes that some 

 of the fish caught on the northern part of Georges 

 Bank in August 1896, were packed with crab 

 larvae, others were full of Sagittae, others, again, 

 of Sagittae and amphipods (Euthemisto) , of small 

 copepods (Temora), or of red feed (Calanus), so 

 that even fish from the same school had selected 

 the various members of the drifting community 

 in varying proportion. 



' See Sette, Fish. Bull. U. S. Fish and Wildlife Service, vol. 51, Bull. 49, 

 1950, p. 267, for further discussion of this point. 



» Sette (Fish. Bull, U. S. Fish and Wildlife Service, vol. 51, Bull. 49, 1950, 

 p. 257) mentions one winter record from about 40° (4.5° C.) on Georges Bank. 



1 Lebour (Jour. Mar. Biol. Assoc. United Kingdom, vol. 12, N. Ser., No. 

 2, 1920, p. 305) gives diet lists for 90 larval mackerel ranging from 5 mm. to 

 13.5 mm. in length, taken in the English Channel. 



