322 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



The immature fish feed and fatten from the 

 time they appear in spring. And it also seems that 

 the schools of older fish destined to spawn late in 

 the season feed until the actual ripening of their 

 sexual products commences, for large catches of 

 the maturing fish were regularly made on hook 

 and line in June in the Gulf of St. Lawrence where 

 spawning takes place in July (until the eggs began 

 to run, in fact). But these large mackerel would 

 not bite after that until they had spawned out 

 (last half of July or first part of August). And 

 available evidence, American as well as European, 

 is to the effect that fish destined to spawn soon 

 after their vernal appearance inshore continue 

 their winter fast until they have spawned, when 

 they commence feeding greedily. 



Enemies. — The mackerel falls easy prey to all 

 the larger predaceous sea animals. Whales, 

 porpoises, mackerel sharks, threshers, dogfish, 

 tuna, bonito, bluefish, and striped bass take heavy 

 toll in particular. Cod often eat small mackerel; 

 squid destroy great numbers of young fish less 

 than 4 or 5 inches long, and sea birds of various 

 kinds follow and prey upon the schools when these 

 are at the surface. A considerable list of parasitic 

 worms, both round and trematode, are known to 

 infest the digestive tract of mackerel. But they 

 seem more immune to danger from sudden un- 

 favorable changes in their environment than the 

 herring are, for they are never known to be killed 

 by cold, and they seldom strand, except when small 

 ones are driven ashore by larger fish. 



Breeding. — Mackerel spawn off the American 

 coast from the latitude of Cape Hatteras to the 

 southern side of the Gulf of St. Lawrence. The 

 spawning area covers almost the entire breadth of 

 the continental shelf southward from Cape Cod, 

 but it is confined more closely to the vicinity of 

 the coast thence northward. Available data 

 point to the oceanic bight between Chesapeake 

 Bay and southern New England as the most 

 productive area, the Gulf of St. Lawrence as con- 

 siderably less so, and the Gulf of Maine and coast 

 of outer Nova Scotia as ranking third. 8 Mackerel 

 do not resort to any particular breeding grounds, 

 but shed their eggs wherever their wandering 

 habits have chanced to lead them when the sexual 

 products ripen. It follows from this, and from the 



> See Sette (Fish. Bull. U. S. Fish and Wildlife Service, vol. 50, Bull. 38, 

 1943, pp. 158-164, and especially fig. 3) for discussion of spawning seasons and 

 temperatures, and the relative importance of different spawning areas. 



fact that mackerel vary so widely in abundance 

 over periods of years that the precise localities of 

 greatest egg production may be expected to vary 

 from year to year, depending on the local concen- 

 trations of the fish. 



The mackerel spawns in spring and early 

 summer. As it does not commence to do so until 

 the water has warmed to about 46° F. (8° C), 

 with the chief production of eggs taking place in 

 temperatures of, say, 48° to 57°, the spawning 

 season is progressively later, following the coast 

 from south to north. Thus the chief production 

 takes place as early as mid-April oft' Chesapeake 

 Bay; during May off New Jersey; in June off 

 southern Massachusetts and in the region of 

 Massachusetts Bay; through June off outer Nova 

 Scotia; and from late June through early July in 

 the southern side of the Gulf of St. Lawrence, 

 where eggs have been taken from early June to 

 mid-August. 9 Mackerel have never been found 

 spawning in autumn, so far as we can learn, 

 though a considerable number of eggs that we 

 towed in Massachusetts Bay early in November 

 of 1916 resembled mackerel eggs from the hatchery 

 so closely that we would not have hesitated to 

 identify them as such, bad they been taken in 

 summer. They may have been the product of a 

 belated fish, but more likely of some other Scom- 

 broid. 



The mackerel is a moderately prolific fish; 

 females of medium size may produce as many as 

 400,000 to 500,000 eggs in the aggregate, according 

 to various estimates, 10 with 546,000 reported for 

 one weighing 1% pounds. But it is seldom that 

 as many as 50,000 are set free at any one time, 

 and often many fewer, for the members of a given 

 school spawn over a considerable period. And 

 recent observations u have shown that our earlier 

 statement that they spawn chiefly at night was 

 not correct. 



The eggs are 0.97 to 1.38 mm. in diameter, with 

 one large oil globule, 12 and drift suspended in the 

 water, chiefly shoaler than the 5-fathom level. 

 The rate of development is governed by the 



• See Sette (Fish. Bull. U. S. Fish and Wildlife Service, vol. 50, Bull. 38, 

 1943, pp. 158-163) for a more detailed statement. 



» Brice, Manual of Fish Culture, 1898, p. 212; Moore, Rept. U. S. Coram. 

 Fish. (1898) 1S99, p. 5; Bigelow and Welsh, Bull. U. S. Bur. Fish., vol. 40, 

 Pt. 1, 1925, p. 208. 



" Sette, Fish. Bull. U. S. Fish and Wildlife Service, vol. 50, Bull. 38, 1943, 

 p. 165. 



" A series of Gulf of Maine eggs measured by Welsh were about 1.1-1 .2 mm. 

 in diameter, with an oil globule of 0.3 mm. 



