often occurs in narrow streaks, and shifts from day to day with winds and 

 currents; it may override shelf water and vice versa. 



Surface circulation in the North Atlantic is very complex and has been 

 analyzed by Bumpus (1973). Generally, surface circulation through the Chesa- 

 peake Bight flows over the Continental Shelf, parallel to the coast line from 

 northeast to southwest. Along the steep Continental Slope, currents may slide 

 off to the east or flow northeastward opposite the inshore current. 



The temperature structure of surface water over the Continental Shelf 

 along the eastern North American coast has been colorfully illustrated by 

 Walford and Wicklund (1968). A summary of mean monthly temperatures on the 

 Continental Shelf along the 38°N parallel has been taken from their work and 

 is presented in Table 7. Surface water passes through an annual cooling and 

 warming cycle, reaching its lowest mean temperature in March, and its highest 

 mean temperature in late August in the northern Chesapeake Bight. Generally, 

 the surface temperature gradually warms with increasing distance from shore. 

 Wind and seasonal air temperatures have the most immediate and noticeable 

 effects on shallow coastal waters, while deep offshore waters are more stable 

 due to the tempering influence of the Gulf Stream and slope water. 



The phytoplankton component of the microbiotic community in offshore 

 waters south of Cape Cod is little known (Smayda 1973, Bureau of Land Manage- 

 ment 1977), but the zooplankton component is fairly well known (Jeffries and 

 Johnson 1973). In general, temperature and salinity have the most pronounced 

 effects on the abundance and distribution of plankton. 



Ovchinnikov (1971) noted that plankton often flourished in nearshore 

 regions where less saline coastal waters mix with more saline oceanic waters. 

 One such area may exist along the 30 fathom contour off the coast of Maryland, 

 where numbers of seabirds and cetaceans, notably fin whales and saddleback 

 dolphins, were often gathered. This area is also an important fishing ground 

 used by small commercial American vessels year round and sports fishermen 

 seeking white marlin ( Makaira albida ) during the summer. Between the 40 and 

 100 fathom contour, a void often exists in the distribution of birds and 

 cetaceans. Activity usually increases again along the edge of the Continental 

 Shelf and over the canyons. The major canyons in the northern Chesapeake 

 Bight (Wilmington, Baltimore, Washington, and Norfolk (— see Fig. 1) are 

 gashes in the edge of the Continental Shelf, whose walls are V-shaped in 

 profile, with the bottoms sloping seaward. The steep walls are rocky whereas 

 the gradually sloping shelf is covered with soft sediment. The mixing of 

 southward flowing surface currents over the edge of the Shelf and canyon, with 

 cold, nutrient rich bottom currents, yields areas of high primary productiv- 

 ity. Zooplankton flourishes in these areas and fish, birds, and cetaceans 

 sometimes congregate. These canyon areas were prime fishing grounds for 

 vessels of the foreign fishing fleets before the 200 mile (322 km) territorial 

 fishing limits were imposed in March 1977. 



66 



