The distribution of marine birds and cetaceans is undoubtedly related to 

 physical and biotic characteristics of oceans. Unfortunately, most marine 

 biologists and oceanographers do not relate the physical and biotic environ- 

 ment to birds and mammals; and most ornithologists and cetologists are not 

 oceanographers. Also, the relative inconvenience and expense of studying 

 pelagic life limits our understanding of how oceanic factors affect seabird 

 and cetacean abundance and distribution (Ainley 1976). Regardless of the 

 above, Ashmole (1971) Shuntov (1972), and Brown (1976) have presented excel- 

 lent discussions of the marine environment relative to the ecology of sea- 

 bi rds . 



Iselin (1936) classified four regimes of oceanic waters adjacent to the 

 east coast of the United States based on salinity -- coastal or shelf water, 

 slope water, Gulf Stream, and ocean water. 



Coastal water, as the name implies, is restricted to areas over the 

 Continental Shelf. It is the least saline because it is subjected to fresh 

 water run-off from the mainland. The greenish appearance on the water is 

 attributed to suspended sediments. Shelf waters are productive feeding areas 

 for non-pelagic seabird species; they were most often seen in these waters. 



Slope water is a mixture of Gulf Stream and shelf waters and is usually 

 present from the Continental Slope, to the western margin of the Gulf Stream 

 where it often forms a conspicuous green-blue interface. In the northern 

 Chesapeake Bight, slope water is visible during the summer months, especially 

 from July through September when it often laps over the Continental Shelf, 

 inshore to the 30 fathom contour. It can be easily recognized by its blue 

 color, a characteristic of high salinity. 



The Gulf Stream flows northeastward along the edge of the Continental 

 Shelf from the Florida Straits to Cape Hatteras, where it then veers east ward 

 away from th^ Continental Slope and out over open ocean. The western margin 

 usually pas^ jout 150 km southeast of the edge of the Continental Shelf at 

 Baltimore Canyon, 38°10'N, 73°50'W (Fig. 1). The Gulf Stream is prone to 

 meandering off its central axis, especially north and east of Cape Hatteras 

 late in the summer, and occasionally, eddies spin off and drift northward 

 along the Continental Slope into the northern Chesapeake Bight. 



The ocean waters of the Sargasso Sea lie beyond the Gulf Stream and have 

 no significant bearing on the fauna observed in the northern Chesapeake Bight. 



The occurrence of warm slope waters and Gulf Stream eddies in late summer 

 coincides with the presence of mats of sargasso weed ( Sargassum sp. ), Portu- 

 guese man-of-war ( Physalia sp.), flying fish (Exocoetus sp.), and those 

 seabirds and cetaceans which are usually associated with warm tropical and 

 Gulf Stream water. These include Audubon's shearwaters, black-capped petrels, 

 white-tailed tropicbirds, bridled terns, spotted do1phins( Stenella plagiodon ), 

 striped dolphins (S. coeruleoalba ),and short finned pilot whales ( Globicephala 

 macrorhynchus ). 



Late summer distribution of the blue slope water over the Shelf in the 

 northern Chesapeake Bight is often spotty, and Maury (1963) noted that it 



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