THE SEA FISHERIES OF EASTERN NORTH AMERICA. 55 



seasons are caused by the reproductive instinct, by conditions of tem- 

 perature, and by search for food. They are also to a less degree 

 affected by the pursuit of predaceous fish and other fellow occupants 

 of the ocean and by the action of man. 



Temperature of the water. — The most important of these agencies is 

 probably that of temperature; since while tfyere are certain species 

 that appear to be quite insensible to considerable variations in this 

 respect, the distribution of others is largely dependent upon the degree 

 of heat in the water. Certain fishes, such as the cod and herring, are 

 to be taken only in cold water, the herring usually at a temperature not 

 exceeding 50° to 55°; tbe cod at a still lower degree. This relation- 

 ship has an important bearing upon the herring fisheries ; since, when 

 the heat of the surface water is above the degree indicated, herring 

 are seldom seen ; as this decreases they make their appearance. This 

 is so well established that now the herring fishery on the coast of Scot- 

 land is largely regulated by the temperature observed, and when it is 

 decidedly above 55° the herring are not looked for. 



On the coast of the United States there are two well-defined regions, 

 one bounded to the south by Cape Cod and the other having this 

 boundary as its northeastern limit. A few stragglers may be found 

 occasionally on either side; but practically the cape constitutes the 

 boundary line. 



As a general rule the winter temperature of the ocean at different 

 points along the New England coast is about the same, the surface 

 water as well as that at the bottom showing the minimum degree down 

 to absolute freezing. During this season, therefore, all the more delicate 

 fish leave either to go south or off the shore until they find the tempera- 

 ture they require ; possibly, however, not until they reach the edge of 

 the Gulf Stream. The summer temperatures, however, vary extremely, 

 and these variations are accompanied by the presence or absence of 

 fish of different kinds. On the south side of New England the warmest 

 temperatures observed were in Peconic Bay, where, in August, 1874, 

 the bottom temperature was from 71° to 72£°, the surface temperature 

 in one instance being as high as 74°. Here the same southern types of 

 marine animals were predominant. 



At Wood's Holl, in 1873, the mean temperature at the bottom in 

 June was 61.7°, and in July 69.5°, and in August 70°/or an average 

 of 67°. The surface was sometimes a few degrees higher. 



Elsewhere on the south side of New England the bottom temperature 

 ranged from Gl° to G5° off the coast of Connecticut, in from 4 to 20 

 fathoms; in rather deeper water from 58.5° to 64°. Off Cox's Ledge 

 it was 50° at 52 fathoms in August, and off several miles northwest of 

 Block Island it was 45.5° at 47 fathoms, this being accompanied by a 

 somewhat different fauna. In general, we may say that south of Cape 

 Cod, while the inshore surface of the water during midsummer ranges 

 from 62° to 70°, at a greater distance outward, up to perhaps fifteen or 

 twenty miles, it ranges from 02° to 68°, and that at the bottom, inside 



