FISHES OF THE GULF OF MAINE 203 



It would be very interesting to test by histologic examination Bullen's obser- 

 vation that the kind of diet influences the anatomic condition of the walls of the 

 stomach of the mackerel, these being very thick and contracted while the fish are 

 feeding chiefly on vegetable foot! and thin and distensible while they are feeding 

 on animal food. Until this subject is studied afresh we can only say that Bullen's 

 note stands alone. 



Most authors describe the mackerel as feeding by two methods — either filter- 

 ing out the smaller pelagic organisms from the water by the gill rakers or selecting 

 the individual animals by sight — but as the branchial sieve of the mackerel, which 

 has long rakers on the foremost gill arch only, is not fine enough to retain the smallest 

 organisms these mostly escape by passing through, just as copepods escape most of 

 the whalebone whales. A good deal of discussion has centered about the relative 

 serviceability to the mackerel of these two methods of feeding. Probably the 

 truth is that when forced to subsist on the smallest articles in its dietary it must 

 do so by sifting them out of the water, but that whenever opportunity offers to 

 exercise its sight it selects the more desirable. This is a question of size, nor is it 

 yet known how small objects the fish is able to pick out. Fish, of course, and such 

 large Crustacea as euphausiid shrimps and amphipods it takes individually, just 

 as the herring does. Judging from the fact that mackerel stomachs are often full 

 of Calanus or of one or two other sorts of food in localities where indiscriminate 

 feeding would yield them a variety, it is evident that this also applies to the larger 

 copepods. Whether they select the smaller copepods and crustacean larvae is not 

 so clear. Captain Damant, 51 whose experience in deep-sea diving has given him 

 an exceptional opportunity- to observe mackerel feeding under natural conditions, 

 describes fish among which he was at work as congregating about some 20 to 40 

 feet below the ship anchored in Lough Swilly (Ireland) and "feeding on plankton, 

 not by steadily pumping the water through the gill filters but snatching gulps 

 from different directions * * * and making little jumps here and there." 



It has been a commonplace from the earliest days of the mackerel fishery that 

 the fish, fat when last seen in the autumn, are very thin when they reappear in 

 spring, obviously suggesting that they feed little during the winter, which is cor- 

 roborated by the fact that the mackerel taken on bottom by British and French 

 trawlers between December and March are almost invariably empty. A con- 

 siderable body of evidence has been gathered in European waters to the effect that 

 such of the European fish as are old enough to breed continue to fast after coming 

 in on the coast until they have spawned, when they commence feeding greedily. 

 In general the results of the American fishery, while it was carried on by hook and 

 line, corroborated this for the June spawning schools of the Massachusetts Bay 

 region. But it is certain in American waters that schools that are destined to spawn 

 late in the season feed until the actual ripening of their sexual products commences, 

 for in the Gulf of St. Lawrence, where spawning takes place in July, large catches 

 of the maturing fish were regularly made in June — in fact, until the eggs began to 

 run. These large mackerel would not bite thereafter until they were spawned 

 out, which happens by the last half of July or first part of August. 



« Nature, Vol. CVIII, Sept-Dec, 1921, pp. 12-13. London. 



