BIOLOGY OF THE ATLANTIC MACKEREL 159 



Season. — Spawning begins in the southern end of this region during the middle 

 of April about as soon as the mackerel appear in the offing of Chesapeake Bay. 

 Thence it proceeds northeastward along the coast, taking place during the month of 

 May off the New Jersey and New York coasts and extending into June off southern 

 Massachusetts. In 1932, spawning in this region reached its climax about the middle 

 of May. (See table 5.) Surveys of other spawning seasons indicate that this is the 

 usual time of maximum spawning. 



Temperature at spavming. — In this region we have found mackerel eggs in water 

 as cool as 7.3° C. (45° F.) and as warm as 17.6° C. (64° F.). In 1932, the greatest 

 numbers of eggs (98 percent) were found in water of 9.0° to 13.5° C. (48° to 57° F.) 

 and this may be regarded as the range in which the bulk of mackerel eggs are usually 

 spawned in this region. 



Gulf of Maine 



Numbers and distribution. — On visits to the western portions of the Gulf of 

 Maine during the present investigation, eggs were found only in Cape Cod Bay. 

 There the concentration was only slightly less than in waters south of Cape Cod 

 but practically none were found in waters off the outer face of Cape Cod and the coast 

 between Boston and Cape Elizabeth. Moore (1899) found them in the outer por- 

 tions of Casco Bay in 1897, but the numbers were few. Bigelow and Welsh (1925 ; 

 p. 206) occasionally found a few in various parts of the Gulf of Maine. The maximum 

 haul was recorded by them as "200 plus." 



Although Bigelow and Welsh (1925, p. 207) say, "That Nantucket Shoals, 

 Georges Bank, and Browns Bank, like the Scotian banks to the east, are also the 

 sites of a great production of mackerel eggs is proven by the ripe fish caught there 

 * * * ", it now hardly appears likely that these banks around the periphery of the Gulf 

 of Maine can be the site of important spawnings. The records of eggs taken by 

 Bigelow and Welsh did not include any from these banks and during the present 

 investigation the waters about Nantucket Shoals were visited repeatedly, and the 

 western half of Georges Bank occasionally, without finding more than negligible 

 numbers there. It is likely that the ripe fish caught on these grounds were a part 

 of schools destined to spawn elsewhere, presumably the Gulf of St. Lawrence, and 

 were taken during the course of migration to that area. This is in harmony with 

 the results of investigations on migration which are to be reported on in another 

 paper of this series. 



Thus it appears that the only spawning ground regularly important in the Gulf 

 of Maine is Cape Cod Bay. This body of water is so small compared with the grounds 

 south of Cape Cod or with those of the Gulf of St. Lawrence that reproduction in the 

 Gulf of Maine must be negligible compared with that of the other spawning regions. 



Season. — Spawning probably takes place somewhat later in the Gulf of Maine 

 than south of Cape Cod in consequence of later vernal wanning and later incursion 

 of mackerel into the waters of this region. It evidently was on the increase and per- 

 haps near its maximum in Massachusetts Bay between June 9 and June 14 of 1926, 

 when hauls taken on a hue of three stations running out from Wood End Light 

 toward the middle of Cape Cod Bay averaged 700 and 1,200 per tow on June 9 and 

 14, respectively. A more precise determination of the time of maximum spawning 

 awaits the sorting of additional hauls made in 1926 and 1930. 



 L I B R A R Y } =o 



