FISHES OF THE GULF OF MAINE 



321 



Similarly, 1,000 mackerel caught near Woods 

 Hole from June to August contained pelagic 

 amphipods (Euthemisto) , copepods, squid, and 

 launce; 4 others taken off No Man's Land have 

 been found full of shelled pteropods (Limacina). 

 And a series of small fish examined by Vinal 

 Edwards contained copepods, shrimps, crustacean 

 and molluscan larvae, annelid worms, appendi- 

 cularians, squid, fish eggs, and fish fry such as 

 herring, silversides, and launce. In short, prac- 

 tically all the floating animals, not too large or 

 too small, regularly serve for the nourishment of 

 mackerel except the Medusae and ctenophores, 

 and a diet list for any given locality would include 

 all the local pelagic Crustacea and their larvae. 



Mackerel have often been seen to bite the 

 centers out of large Medusae, but, as Nilsson 

 suggests, they probably do this for the amphipods 

 (Hyperia) that live commensal within the cavities 

 of the jellyfish, not for the sake of the latter. 



Mackerel also eat all kinds of small fish, to a 

 greater or less extent according to circumstances. 

 In the Gulf of Maine they devour large numbers 

 of small herring, launce, and even smaller mack- 

 erel. They likewise feed on pelagic fish eggs 

 when available, oftenest on those of their own 

 species. And they bite greedily on almost any 

 bait, especially if it moves, such as a bit of mack- 

 erel belly skin, a piece of clam, a piece of sea worm 

 (Nereis), a shining jig, spoon or spinner of appro- 

 priate size, or an artificial fly, white, red, or silver- 

 bodied. Side by side with these comparatively 

 large objects mackerel are also known to take 

 various microscopic organisms, chiefly the com- 

 moner peridinians and diatoms, but they never 

 feed extensively on these as menhaden do (p. 114). 

 And copepods are so plentiful in the Gulf of 

 Maine, and the vegetable plankton that swarms in 

 April has so largely disappeared over most of the 

 Gulf before the mackerel appear later in the 

 spring, that we doubt if they are ever reduced to 

 a vegetable diet there or anywhere in American 

 waters. 



Mackerel are also known to feed on bottom 

 animals to a small extent. Nilsson, for example, 

 reports various worms and hydroids and even 

 small stones from their stomachs, but our expe- 

 rience in the Gulf of Maine is to the effect that 

 this would be exceptional there, if it happens at all. 



' Nilsson (Publ. de Circ, Conseil Perm. Internat. Eiplor. Mer, No. 69. 

 1914) gives a similar list for Swedish waters 



210941—03 22 



Most authors describe the mackerel as feeding 

 by two methods: either by filtering out the smaller 

 pelagic organisms from the water by their gill 

 rakers 5 or by selecting the individual animals by 

 sight. A good deal of discussion has centered 

 about the relative serviceability of these two 

 methods of feeding. Probably the truth is that 

 when forced to subsist on the smaller objects in its 

 dietary it must do so by sifting them out of the 

 water, but that it selects the more desirable when- 

 ever opportunity offers to exercise its sight. It is 

 not yet known how small objects the fish is able to 

 pick out. It takes fish individually of course, and 

 such large Crustacea as euphausiid shrimps and 

 amphipods, just as the herring does, which evi- 

 dently applies to the larger copepods, to judge 

 from the fact that mackerel stomachs are often 

 full of Calanus or of one or two other sorts in 

 localities where indiscriminate feeding would yield 

 them a variety. Whether they select the smaller 

 copepods and crustacean larvae is not so clear. 

 Captain Damant, 6 whose experience in deep-sea 

 diving has given him an exceptional opportunity 

 to observe mackerel feeding under natural condi- 

 tions, describes fish among which he was at work 

 20 to 40 feet deep in Lough Swilly (Ireland), as 

 "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 are fat 

 when last seen in the autumn, but that most of 

 them are thin when they reappear in spring, 

 obviously suggesting that they feed little during 

 the winter. This is corroborated by the fact that 

 the mackerel taken on bottom by British and 

 French trawlers between December and March 

 usually are empty, and that a few mackerel taken 

 by the Albatross II along the continental edge off 

 Chesapeake Bay in February 1931 were very 

 emaciated. But mackerel taken in winter some- 

 times have food in their stomachs; some of them 

 even are fat. 7 



• The mackeral has long rakers with spines on the foremost gill arch only, 

 and these are not fine enough to retain the smallest organisms. See Bigelow, 

 Bull. U. S. Bur. Fish, vol. 40, Pt. 2, 1926, fig. 42 C, D for photographs of the 

 gill rakers. 



• Nature, vol. 10S, 1921, pp. 12-13. 



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

 pp. 259, 202) reports some fat mackerel in winter. 



