In February 1962, the direction of surface drift over the continental 

 sheH in the northwestern Gulf of Mexico was generally westerly, ranging in 

 rate from 0.4 to 0. 7 knots. An easterly drift of 0. 3 to 0. 6 knots was observed 

 between Brownsville and St. Joseph Island, Tex. The higher rate is near the 

 shore. There are indications of a large clockwise circulation developing in 

 the vicinity of Port Aransas. Returns for the mmths of March through June 

 tend to corroborate this impression, but its exact nature is not yet clear. A 

 second smaller eddy apparently exists in the area off Grand Isle, La. 



The seabed drifter previously described is a plastic umbrellalike 

 device that barely maintains itself on the bottom, so that even very small 

 water movements will cause it to drift along the bottom. It is largely depend- 

 ent for its return, therefore, upon capture in shrimp trawls, although many 

 liberated at inshore stations have been found on the beach. Their rate of re- 

 turn, except for the beach finds, is closely related to fishing effort, which 

 varies extensively according to time and area, causing returns from this 

 source to be slow and erratic. Shrimp trawlers in the Gulf of Mexico carry 

 a minimum of navigation equipment, and the location of the return is often 

 too vague to be of use. Despite these limitations, some useful information 

 has been obtained. During February 1962, bottom drift, based on 16 returns, 

 was generally easterly or opposite to surface drift except in the area off 

 Grand Isle, La. , where the bottom drift was northerly or westerly. 



The direct measurement of water movements by drift bottles and 

 seabed drifters is continuing; indirect measurement by analysis of density 

 currents is planned. 



Comparison of returns for ballasted and nonballasted 

 drift bottles as of July 1, 1962 



26 



