FISHES OF THE GULF OF MAINE 427 



or seasons west of Nantucket. On the other hand, cod eggs are produced in pro- 

 fusion as far north as the Gulf of St. Lawrence and the Grand Banks, but it is not 

 known how much spawning takes place along the eastern coast of Labrador. 



Cod spawn in shoaler water than haddock. In fact, we can find no record of 

 ripe fish deeper than 50 fathoms, and most of the Gulf of Maine spawning takes 

 place on much shoaler bottoms. The Georges Bank ground, for example, is about 

 25 to 35 fathoms deep; the Nantucket grounds are hardly anywhere deeper than 

 20 fathoms and as shoal as 7 fathoms in places; the Massachusetts Bay grounds 

 are about 12 to 25 fathoms; and the Ipswich Bay ground only 5 to 25 fathoms 

 according to the precise locality. In short, very few, if any, cod spawn deeper than 

 30 fathoms in the Gulf, and on the inshore grounds the major production of eggs 

 takes place in water shoaler than 15 fathoms. We wish to emphasize the fact that 

 no cod breed anj^where in the central deeps of the Gulf outside the 50-fathom 

 contour. 



With the breeding grounds of the cod so localized and spawning taking place 

 close to bottom, and ^nih the chief production of eggs during the cold months, the 

 physical state of the water in which eggs are produced can be stated with some 

 confidence at an^ particular locality and date, but corresponding to the prolonged 

 period of reproduction spawning takes jjlace over rather a wide range both of 

 temperature and of salinity. On the Ipswich Bay grounds, for example, ripe fish 

 are taken when the bottom water is still as warm as 44° to 46° (early September), 

 but they appear in greater numbers in temperatures of 41° to 43° (January); and 

 as the breeding season progresses the temperature falls, spawning being at its 

 height in the minimmn temperatures of the year (March) — that is, 33° to 37.5° — 

 though the fish continue to spawn until the bottom water has once more warmed 

 to 38° to 41° (mid-May). 



On the Massachusetts Bay ground the peak of the spa^vning season is reached 

 and passed before the temperature drops to its winter minimum, hence in decidedly 

 warmer water than in Ipswich Bay, spawning fish appearing in numbers (late 

 November) while the bottom water is still as warm as 44° to 47°, with the chief 

 production taking place in temperatures of 36° to 42° (December, through January). 

 Most of the spawning takes place in the falling temperature on this ground, although 

 some cod breed there right through the coldest season (minimum temperature 33° 

 to 37°). The temperature range through which the cod breed on the offshore 

 grounds can not be stated so precisely, for want of autumn and early wdnter data. 



Cod kept in captivity at Woods Hole spawn freely through an equally wide 

 range of temperature, eggs even being produced (and quite normally, to judge 

 from the successful incubation of the resultant eggs in the warmer water of the 

 hatchery) in February when the pool may have cooled to 30°, an interesting fact, 

 for if left at liberty the fish in question would have spa-wned naturally in water at 

 least as warm as 36° to 38°. Cod spawn in water as cold as 32° in the Gulf of 

 St. Lawrence and probably also on the NeA\'foundland Banks."* 



•• Hjort. Canadian Fisheries Expedition, 1914-15 C1919), P- xxvii. 



