STUDY AREA 



The Pilot Study aerial surveys were conducted entirely within the U.S. waters of 

 the Gulf of Mexico. The Gulf of Mexico is a contiguous embayment of the north Atlantic 

 Ocean encompassing some 1,640,000 km 2 . Bordered largely by the United States, 

 Mexico, and Cuba; its two main avenues of water exchange are the Yucatan and Florida 

 submarine channels. 



The continental shelf is variable in width but most of the coastline is 

 characterized as having an extensive shelf. Widths vary from 185 km and 215 km off the 

 West Florida and Yucatan coasts, respectively, narrowing to 25 km off the Rio Grande 

 Outlet and 13 km near Vera Cruz, Mexico (Lynch 1954). The transition from a wide to 

 narrow shelf is rather abrupt west of Campeche, Mexico, and southwest from 

 approximately Galveston, Texas. The Desoto Canyon briefly interrupts the wide shelf off 

 the panhandle region of Florida. 



Currents are complex in origin but the basic pattern is analogous to that of the 

 North Atlantic (Sturges and Blaha 1976). External input is largely from the Caribbean 

 via the Yucatan Channel. Output is largely through the Florida Channel which 

 contributes to the Gulf Stream. The micro-tidal range and the dominance of diurnal 

 components (Marmer 1954) result in an increased importance of meteorologic forces on 

 water circulation. 



Two dominant meteorologic regimes characterize the region: the Bermuda High 

 and mid latitude frontal passages. The Bermuda High dominates the area with wind 

 speeds generally being the strongest during the summer months when the elimatologic 

 equator reaches its northern limits. Surface water temperatures are typically uniform 

 over the Gulf of Mexico at this time, averaging some 28° C over the continental shelf 

 and slightly cooler over the central Gulf of Mexico (Leipper 1954). During winter, 

 gradations of surface water temperatures are more conspicuous. Temperatures generally 

 range from 18.5° C in the northern Gulf of Mexico to 25° C off the Yucatan Peninsula 

 (Leipper 1954), reflecting the increasing influence of mid latitude frontal passages 

 followed by cooler polar air. Tropical disturbances, of which hurricanes are the most 

 intense, form a third weather regime. Although infrequent, these disturbances often 

 result in dramatic environmental alterations. 



There is an appreciable difference in the extent of human activities along the 

 Florida and Texas coasts. The offshore oil activities and associated tanker traffic, along 

 with the shrimp industry, are more intense along the Texas coast than off Florida. 



In both Florida and Texas, the northern survey subunits described in this report 

 occur in the vicinity of major shipping lanes and receive more commerical ship traffic 



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