THE ORIGIN, RELATIONSHIPS, AND GEOGRAPHICAL DISTRIBUTION OF 

 THE MARINE FISHES OF THE GULF OF MEXICO' 



By Luis Rene Rivas, University of Miami 



The Gulf of Mexico is the northwest ernmost of 

 the three Middle American basins. It is a typical, 

 basin-shaped mediterranean sea with an area of 

 615,000 square miles and a maximum depth of 

 about 2,000 fathoms (Sigsbee Deep) at its center. 

 Its longest axis, oriented SW-NE between Vera- 

 cruz, Mexico, and Apalachee Bay, Florida, meas- 

 ures about 960 nautical miles, and its short axis, 

 oriented N-S between the Mississippi Delta and 

 the Peninsula of Yucatta, measures about 460 

 nautical miles. The Gulf of Mexico is separated 

 from the Atlantic Ocean by the Straits of Florida, 

 about 110 nautical miles wide between Cape Sable, 

 Florida, and Cabo Hicacos, Cuba, with a maximum 

 depth of about 900 fathoms (average depth about 

 500 fathoms). It is separated from the north- 

 western Caribbean Basin by the Yucatan Channel, 

 about 110 nautical miles wide between Cabo 

 Catochcr Yucatan, and Cabo San Antonio, Cuba, 

 with a maximum depth of about 1,000 fathoms 

 (average depth about 700 fathoms). The total 

 perimeter of the Gulf of Mexico comprises about 

 3,000 nautical miles of which only about 220 (7 

 percent) are taken up by the openings (Straits of 

 Florida and Yucatan Channel). 



The above conditions would seem to indicate 

 that the Gulf of Mexico contains a characteristic 

 fish fauna of its own appreciably distinct from 

 that of neighboring areas. In this respect, how- 

 ever, it is to a great extent a continuation of the 

 Caribbean region, (See Rivas, 1949, for list of 

 game and commercial fishes.) 



There is a very slight amount of subspecific 

 distinction between the fish faunas of the Gulf of 

 Mexico and the Caribbean Sea, and a temperate 

 Atlantic element is present in the Gulf but absent 

 in the Caribbean region. On the other hand, 

 there are several species which occur in the 

 Caribbean region but not in the Gulf of Mexico, 



• Contribution No. 107 from the Marine Laboratory, University of Miami. 



and there is no marlved transition between the fish 

 faunas of the Gulf of Mexico and the Caribbean 

 Sea or the Atlantic Ocean through the Yucatan 

 Channel and the Straits of Florida, respectively. 

 There is relatively little known of the deep-sea 

 fish fauna of the Gulf, but the present depth of 

 the Yucatan Channel and the Straits of Florida 

 cannot be construed as barriers preventing the 

 dispersal of deep-sea fishes to and from the Gulf. 

 According to the paleogeographic evidence (Schu- 

 chert 1935) there was a land barrier across the 

 Yucatan Channel during the Mio-Pliocene, and 

 the Straits of Florida were then shallower than 

 at present. These conditions, however, were 

 relatively short-lived, and their former existence 

 is now reflected in the slight subspecific transition 

 (affecting only very few species) observed through 

 the Yucat&n Channel and the presence or absence 

 of certain forms north and south of this strait. 

 The Gulf Stream, entering from the Caribbean 

 Sea through the Yucatan Channel and leaving 

 through the Straits of Florida, is one of the most 

 important factors in making the fish fauna of the 

 Gulf of Mexico homogeneous with that of the rest 

 of the Caribbean area. 



Among many others, the genera Harengula 

 (Clupeidae), Mugil (Mugilidae), and Centropomus 

 (Centropomidae) will serve to illustrate the above 

 distributional pattern. Of the three species of 

 Harengula (sardines) known from the Caribbean 

 area only H. pensacolae occurs throughout the 

 entire perimeter of the Gulf, being rather scarce in 

 the Caribbean Sea. On the other hand, H. 

 humeralis and H. clupeola are very abundant in 

 the Caribbean Sea but penetrate into the Gulf 

 only as far as the north coast of Yucatan, western 

 Cuba, and southern Florida. Mugil cephalv^s and 

 M. curema are the only mullets occurring through- 

 out the entire perimeter of the Gulf of Mexico, 

 whereas, M. trichodon penetrates only to the 

 north coast of Yucatdn, northwestern Cuba, and 



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