204 BULLETIN OF THE BUREAU OF FISHERIES 



It is a question whether the ripe males fast as rigorously while in breeding 

 condition as do the females, for Cunningham 52 reports taking ripe ones in abundance 

 on hook and line, but no females, at a locality where gill nets were yielding ripe 

 fish of both sexes. The immature fish feed from the time they appear in spring, 

 and the spent fish, very thin from then- effort of breeding, at once commence eating 

 and putting on fat, until by autumn they are in the best of condition for the winter 

 or for the table. 



Enemies. — Due to its habit of schooling the mackerel falls easy prey to all 

 the larger predaceous sea animals. Whales, porpoises, mackerel sharks, threshers, 

 dogfish, tuna, bonito, and bluefish in particular take heavy toll. Cod often eat 

 small mackerel, squid destroy great numbers of young fish less than 4 or 5 inches 

 long, and when the schools are on the surface sea birds of various kinds follow and 

 prey upon them. A considerable list of parasitic worms, both round and trematode, 

 are known to infest the digestive tract of mackerel, but so far as actual recorded 

 observation goes they seem more immune to dangers from sudden unfavorable changes 

 in their environment than are the herring, for instance, for they are never known 

 to be killed by cold and seldom strand. 



Rate of growth.- — Although mackerel often spawn in abundance in the Gulf of 

 Maine practically nothing is known of the young fish there until they are about 2 

 inches long. In North European waters mackerel grow to a length of about three- 

 fourths of an inch within a few weeks after hatching, and numbers of larva? up to 

 this size have been taken about the spawning areas on both sides of the Atlantic. 

 Small mackerel intermediate between these and fry of 2 to 3 inches have seldom 

 been seen, but the latter have been taken repeatedly at many localities, chiefly in 

 July and August, and as they are the smallest sizes so far reported for the late 

 summer they probably represent the hatch of the previous May — that is, they 

 are about 3 months old. In October and November young mackerel of 5 l / 2 to 8 

 inches are taken in abundance in Swedish and British waters, but it is not clear 

 whether these are all the product of that year's hatch, the smaller representing 

 the latest and the larger the earliest spawnings, or whether two year classes are 

 concerned. 53 



Such notes as have been made on the sizes of American mackerel at different 

 seasons correspond to what has just been outlined for the European fish. Thus 

 Captain Atwood found fry of 2 inches or shorter in the Massachusetts Bay region 

 in July, about a month after the local schools, assumed to be their parents, had 

 spawned out, and we have seen mackerel of 1}4 to 2% inches, obviously spawned 

 that spring, taken at Woods Hole during the first half of June. Others of 2 x /i to 3 

 inches have been reported there in July, 54 and fry of 2% to 3% inches along the 

 New York coast during that same month. 55 



" Journal, Marine Biological Association of the United Kingdom, Vol. II, No. Ill, 1892, p. 232. 



» Nilsson's studies (Conseil Permanent International pour l'Esploration de la Mer, Publications de Circonstance No. 63, 

 1914) led him to the former view, but mackerel scales are so difficult to read that this requires confirmation. 



« Sherwood and Edwards, 1902. 



» Bean (The food and game fishes of New York, 1903) also records fry of Z)-i to Vi inches from Long Island as early as May 

 23, 1906, but since mackerel do not commence spawning there until that month it is hard to account for them. 



