RESULTS AND DISCUSSION 



Comparison of Ballasted 

 and Unballasted Drift Bottles 



Because of the use of two types of bottles, i.e., 

 ballasted and unballasted, data were grouped by bottle 

 type to determine if differences existed between rates of 

 recovery (Table 2), direction of drift, and speed of 

 drift. 



Cruise values of percent recovery fluctuated from 22 to 

 54% between Cruise 1-62 and Cruise 6-63. Thereafter, 

 values fluctuated from to 76%, reflecting probably the 

 reduced number of bottles released during this period 

 (Table 1). It was readily apparent that in general fewer 

 ballasted than unballasted bottles were recovered with- 

 in 30 days after release (Table 2). For a comparison of 

 direction and speed of ballasted and unballasted bottle 

 drift, we arbitrarily selected 10 "test groups" for anal- 

 ysis, i.e., stations from which several ballasted and un- 

 ballasted bottles were recovered within 15 days from a 

 single release (Table 3). 



The average direction of both types of bottles was 

 usually similar. One exception was "test 8" in which 

 several ballasted bottles moved southward down the 

 coast, while several unballasted bottles moved north- 

 ward up the coast. Average speeds were also generally 



similar with no definite indication that unballasted bot- 

 tles drifted at a greater rate than did unballasted bottles. 



Surface Circulation 



Over the 2-yr period, surface currents underwent 

 distinct directional shifts which were, in general, similar 

 between years. Because of this, specific months, 

 although illustrated individually, have been grouped, 

 irrespective of years: January-February; March-May; 

 June-July; August; and September-December. 



January-February. — Currents during this period 

 generally paralleled the northwestern Gulf coast, flowing 

 west off Louisiana and becoming southwest off Texas 

 (Fig. 2). Slight deviations from this pattern were ap- 

 parent in 1962 in two areas. Just west of the Mississippi 

 River the flow was to the north and onshore, whereas off 

 the south Texas coast there were indications of an in- 

 shore countercurrent to the north. 



Current velocities ranged from a low of 4 km/day to a 

 high of 14 km/day. Greatest velocities (9-14 km/day) 

 were observed in waters over the central portion of the 

 study area, i.e., off western Louisiana and eastern Texas. 

 Lowest velocities occurred just west of the Mississippi 

 River (5 km/day) and off south Texas (4 km/day) in the 

 vicinity of Brownsville. 



Table 2. — Comparison by cruise of recovery of ballasted and 

 unballasted drift bottles within 30 days after 

 release in the Gulf of Mexico 







Recoveries 





Ballasted / 



Cruise 



Ballasted 



Unballasted 



Total 



Total Recovered 



1-62 



8 



29 



37 



22 



2-62 



27 



53 



80 



34 



3-62 



17 



55 



72 



24 



4-62 



9 



28 



37 



24 



5-62 



21 



36 



57 



37 



6-62 



7 



24 



31 



23 



7-62 



19 



52 



71 



27 



8-62 



7 



14 



21 



33 



9-62 



50 



43 



93 



54 



10-62 



9 



22 



31 



29 



1-63 



9 



9 



18 



50 



2-63 



17 



17 



34 



50 



3-63 



31 



51 



82 



38 



4-63 



25 



45 



70 



36 



5-63 



33 



45 



78 



42 



6-63 



25 



31 



56 



45 



7-63 







2 



2 







8-63 



3 



12 



15 



20 



9-63 



34 



11 



45 



76 



10-63 



8 



5 



13 



62 



11-63 



7 



3 



10 



70 



