1 58 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



SPAWNING GROUNDS AND SPAWNING SEASONS 



Bigelow and Welsh in 1925 (pp. 206-208) summarized the information available 

 on the spawning of the mackerel. Apart from the generalization that mackerel spawn 

 along the American Atlantic coast from Cape Hatteras to the Gulf of St. Lawrence 

 mainly in spring and early summer, most of the conclusions reached at that time are 

 now subject to revision. Their statement (p. 206) " * * * a much greater production 

 of mackerel eggs takes place east and north than west and south of Cape Cod, with 

 the Gulf of St. Lawrence far the most productive nursery for this fish," is particular- 

 ly at variance with present available facts, as will appear from the following account, 

 of the numbers of mackerel eggs found in the various parts of the spawning range. 



Coast of the Southern New England and Middle Atlantic States 



Numbers and distribution. — Until the present investigations there was little known 

 about the spawning in the great bight bordered by the shores of southern New England 

 and the Middle Atlantic States. Although ripe individuals are commonly taken in thp 

 fishery in this area, no appraisal had been made of the egg concentrations to be found 

 there; nor was it known whether larvae hatched from such eggs as were spawned there 

 could survive; in fact it was suspected that reproduction was unsuccessful, for no 

 larvae of the mackerel had been captured there. 



As a result of information gained from the surveys of the present investigation 

 during the seasons 1927-32, this region now appears to contain the most importaut 

 spawning grounds of the mackerel. In horizontal tows at the surface, i. e., in the 

 stratum of densest concentration, a meter net has taken, in 20 minutes, as many as 

 185,000 eggs. In 1929 the average catch per positive tow 3 of this kind was 2,600 

 eggs during the cruise of May 10 to 18, and 5,000 eggs during the cruise of May 28 

 to 31. These numbers may be taken as fairly typical of concentrations at the sur- 

 face when and where spawning is active, and will be useful for comparison with other 

 regions where similar data are available. More informative, in the absolute sense, 

 are the results of oblique tows of 1932, which sampled all levels and covered syste- 

 matically the entire region between Cape Cod and the Chesapeake Capes. The 

 average catch of such tows, including all between May 2 and June 21, i. e., the major 

 portion of the spawning season, and including both positive and negative tows, was 

 slightly over 1,100 eggs. Since these tows strained 17 cubic meters of water per 

 meter of depth fished, the average concentration was 65 eggs per square meter of 

 sea surface. 



Within this region eggs have been consistently most abundant along the inner 

 portions of the continental shelf. The area of densest distribution occupies about 

 the inner half of the shelf off New York with the zone narrowing and trending some- 

 what offshore southerly, and also narrowing but trending inshore northeasterly. By 

 far the greatest concentrations have been found regularly somewhat southerly of the 

 Fire Island Lightship, and this undoubtedly marks the usual center of greatest 

 spawning activity. 



So far as is now known, no spawning takes place in the enclosed waters of the 

 bays and sounds west and south of Block Island. A few eggs are spawned in the 

 southern part of Buzzards Bay and Vineyard Sound, but these are negligible in 

 quantity compared with the spawning in open waters. 



J Positive here indicates a tow in which mackerel eggs were caught. 



