70 MARINE FISHERIES OF NORTH CAROLINA 



temperature on this shelf comparatively warm the year around. The seasonal 

 relationships of this warm area to the rest of the coast are as follows (for a 

 comprehensive discussion of this see Parr, 1933): 



During mid-summer rather uniform temperatures, usually above 78° F., 

 prevail from southern Florida to Cape Hatteras. To the north of Hatteras 

 there is a moderate gradient of decreasing temperatures but no temperature 

 discontinuity or barrier exists short of the cold area around Nantucket and 

 south of Cape Cod. 



Later in the fall a temperature discontinuity appears, as coastal waters cool 

 to the north and south of the general Hatteras region which maintains 

 mid-winter temperatures of about 60° F. under the effects of the Florida 

 Current. 



Because of variations in such factors as the flow and course of the Florida 

 Current, there are relatively great temperature fluctuations in the Hatteras 

 area in winter. 



Cape Hatteras has long been referred to as a temperature barrier to the 

 distribution of marine forms, but these coastal temperature relationships 

 suggest many distribution effects not brought to attention by the barrier 

 concept. A non-migratory organism that requires warm water the year 

 around might be missing along the coast from northern Florida to southern 

 North Carolina and yet be present around Hatteras and offshore to the south 

 of Hatteras. Other non-migrators that tolerate moderate winter cooling might 

 have a coastal distribution as far north as Hatteras and little farther, whereas 

 those requiring cooler water might be found only to the north of this cape. 

 Continuing to deal in categories in order to elaborate on such general tem- 

 perature effects, migratory species may be mentioned under four headings: 

 ( I ) those which undertake northward migrations to cooler waters in summer 

 and probably pass close to Cape Hatteras en route; (2) those requiring sub- 

 tropical temperatures which might be found as far north as Hatteras in 

 summer, though a cold summer upwelling off Daytona, Florida, may interrupt 

 this; (3) those requiring warm waters to the extent that they retreat from 

 the North Carolina sounds and from the coast to the south to a southern 

 winter retreat or possibly to warm waters at the edge of the continental shelf 

 including those in the Hatteras region; and (4) those requiring moderate 

 winter temperatures, retreating from Middle Atlantic and North Carolina 

 coastal points to winter around Hatteras. 



The last is a comparatively well known category of great fisheries sig- 

 nificance. It accounts for the prosperous winter trawl fishery for scup, 

 flounders, croakers, sea bass, etc., which has developed off the Virginia and 

 North Carolina capes in the last two decades. Also, the combined assets of 

 the large shallow North Carolina sounds with a bordering area that remains 



