208 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



of Nova Scotia and south of Newfoundland. Thus 

 we took several unmistakable haddock eggs among 

 numerous newly spawned cod or haddock eggs a 

 few miles off Shelburne on June 23, 1915, while 

 Dannevig w records occasional haddock larvae off 

 Halifax on July 23; near Sable Island on July 25 

 and 26 ; and on St. Pierre Bank off Newfoundland 

 on July 27 and 28 for that same summer. 



The breeding season is about the same in 

 European as in American seas, that is, end of 

 January until June, with the peak of production 

 falling as early as March and April in the North 

 Sea region but not until June around Iceland. 68 



The Georges and Browns Bank haddock spawn 

 in temperatures ranging from about 36.5° to about 

 42°—43° F., and spawning is likewise completed on 

 the coastwise grounds between Cape Cod and Cape 

 Elizabeth before the stratum of water in which 

 the fish are living has warmed more than a few 

 degrees from its coldest for the year; i. e., in tem- 

 peratures of about 35° to 40°— 42°. Allowing for 

 annual variations, this gives an extreme range of 

 from about 35° to about 44° F. for the most active 

 spawning over the Gulf of Maine as a whole, tem- 

 peratures averaging considerably lower than those 

 in which haddock spawn the most freely in Euro- 

 pean waters (41° to 50°). 



The Gulf of Maine haddock likewise spawn in 

 less saline water than does its European congener; 

 and necessarily so, for the more important Gulf of 

 Maine spawning grounds are considerably less 

 saline at all depths and seasons (about 31.5 to 

 33.5 per mille, mostly). 



The specific gravity of the water at the tempera- 

 ture in situ (the factor that determines whether 

 buoyant fish eggs float suspended, and develop, 

 or sink to the bottom and die) is usually between 

 1.0255 and 1.0270 in our Gulf in spawning season, 

 at the depths where the fish spawn, both along 

 shore and on the offshore Banks. Experiments 

 by us and by Walford have shown that these 

 values are high enough for the flotation of the 

 eggs. And while the water at the surface often 

 is so light, near shore, as to interfere with the 

 operation of the hatcheries, this layer of low specific 

 gravity is so thin there is no reason to suppose that 



« Canadian Fish. Eiped. (1914-15) 1919, p. 21. 



" Damas, Rapp. et Proc.-Verb. Cons. Internat. Explor. Mer, vol. 10, 1909; 

 Schmidt, ibid. 



any of the haddock eggs produced in the Gulf fail 

 to rise from the bottom. 69 



Populations and migrations within the Gulf of 

 Maine. — Needler's 70 analysis of the results of 

 tagging experiments, and of the differences in rate 

 of growth between fish caught in different regions, 

 and Vladykov's 71 studies of the number of verte- 

 brae, confirmed by comparison between the 

 growth rates of the haddock of Georges Bank and 

 of Browns Bank by Schuck and Arnold, 72 have 

 shown that the haddock of North American waters 

 include three more or less self-contained popula- 

 tions; one (Needler's "New England population") 

 inhabiting the Georges Bank-Nantucket shoals 

 region and the inner waters of our Gulf from Cape 

 Cod around to the New Brunswick shore of the 

 Bay of Fundy; a second (Needler's "Nova Scot- 

 ian") in the Nova Scotian side of the Bay of Fundy, 

 and around Nova Scotia (including Browns Bank) 

 to the Laurentian Channel; and a third in New- 

 foundland waters. 



The geographic ranges of the New England and 

 Nova Scotian populations are separated by the 

 deep so-called "Eastern Channel" between Georges 

 Bank and Browns, which extends inward as the 

 "Fundian Channel" more than 100 fathoms deep, 

 to the mouth of the Bay of Fundy. And it is 

 probable that the depth is an actual barrier in 

 this case, there being no evidence that haddock 

 normally cross channels that are deeper than 

 about 100 fathoms (at least in American waters), 

 once they have taken to the bottom. Only within 

 the Bay of Fundy, where there is no intervening 

 water as deep as 100 fathoms, have tagging 

 experiments given any evidence of a mixture 

 between these two adult populations. 73 And the 

 still greater depth of the Laurentian Channel 

 probably makes it an even more effective barrier 

 between the Nova Scotian and the Newfoundland 

 populations. 



The movements of individual fish within each 

 of these populations fall in three groups : (a) those 

 of the eggs and larvae while they are still adrift 

 in the intermediate and upper water layers; 

 (b) those of the young fry from the time they take 



89 For a discussion of the relationship between flotation of haddock eggs 

 and the specific gravity of the water, with references to European studies, 

 see Walford, Bull. V. S. Bureau of Fisheries, vol. 49, Bull. 29, 1938, pp. 13-15. 



*> Contrib. Canadian Biol, and Fish., N. Ser., vol. 6, No. 10, 1930. 



" Progress Rept. Atlantic Biol. Sta. Biol. Board, Canada, No. 14, 1935. 



'•- Fish. Bull. No. 67, U. S. Fish and Wildlife Service, 1951. 



T3 One fish that was tagged by us near Mount Desert Island was recaptured 

 in the Nova Scotian side of the Bay of Fundy off Digby. 



