western Gulf is defined as the area west of the meridian between the 

 Delta of the Mississippi and the north coast of Yucatan (longitude 90"^.). 

 It is a convenient geographical boundary and has some biological signif- 

 icance at least in the northern part of the Gulf, as the influence of 

 the Mississippi River is greater to the west than to the east of the 

 Delta, 



Economically there is little reason to divide the Gulf into 

 eastern and western areas. One of the oldest fisheries on the Gulf coast 

 is located in Pensacola, Florida, and snapper fishermen have for years 

 traveled to and from Campeche Banlc. Recently more shrimp from Campecha 

 Banlc have been landed at southern i^lorida ports than in Texas. The 

 migratory character of the shrimp fleet makes it possible for the fisheiraen 

 to fish extensively both in the eastern and westeni Gulf during the course 

 of a single year. 



Structurally, the continental shelf should be considered a part 

 of the bordering coastal plain. The continental shelf varies greatly in 

 width. It is approximately 120 miles ^d.de off Cameron, Louisiana. In 

 Texas it has an average width of sixty miles and is much wider off Sabine 

 than off Port Isabel, The slope of the Texas coastal plain is about five 

 feet to the mile and the slope of the continental shelf is about twelve 

 feet to the mile. The average width of the shelf off Tamaulipas, Moxico, 

 is considerably less than off Texas. Off Punt a Roca Partida in the State 

 of Vera Cruz, Mexico, where the Eastern Sierra Madre Moimtains almost 

 reach the coast, the continental shelf is correspondingly narrow and 

 steep, being approximately eight miles wide. In the vicinity of Campeche,' 

 Mexico, the shelf is ninety miles wide, and the abrupt seaward escar-praont 

 of Campeche Dank is probably due to dovm-faulting. 



The bottoms of the continental shelf are described as follows; 

 beyond the 10-fathom curve the bottom is primarily terrigenous mud or 

 silt, but with mixtures of sand extending out to thirty or more fathoms 

 in some areas. Mud lumps and large coral-rock otructiires are common 

 beyond the 50-fathom curve out to the edge of the shelf. If the conti- 

 nental shelf wore a smooth area, everyi/here suitable for the operation 

 of the otter trawl, it v/ould be much simpler to map the concentrations 

 of shrimp. The abundance of shriinp in areas not suitable to trawling 

 can only be surmised. 



All four species of shrimp now commercially exploited in the 

 Gulf of Moxico are caught on the continental shelf. The broim-grooved 

 shrirap, Penaaus aztecus , is the principal species found in catches from 

 the extensive mud bottoms of the continental shelf of Alabaaia, Mississippi, 

 Louisiana, and Texas. White shrimp, Penaous setiferus , are also present 

 in the same region. In the Gulf of Cajnpeche ijuportant commercial fishing 

 grounds for the above-named two species and for pink shrimp, Penaeua 

 duorarum, exist in contiguous areas. Pink shrimp are taken in abundance 

 off Key West and the Dry Tortugas. Sea bob, Xiphopeneus kroyeri , is 

 found primarily in the estuarlal waters of Louisiana, 



18 



