35 



Current Directions 

 Seasonal — 



^ 



/ 



K/ 





-15" 



ti^.' 



460° 



Figure 4. — Surface water circulation in the study area. 



From data collected on the 1965 cruise, Tibbo 

 and Lauzier (1969) proposed a spawning ground for 

 Gulf Stream larvae west of the Straits of Florida. 

 They assumed that larvae from both the Florida 

 Straits and Cape Hatteras areas came from the 

 same spawning area. From this, they calculated a 

 growth rate of 2mm/day and, using back calcula- 

 tions similar to Arata's, placed the spawning 

 grounds in the southern Gulf of Mexico, and prob- 

 ably in the Yucatan Channel. However, when other 

 data are considered, it is obvious that this region is 

 not the only spawning ground in the western Carib- 

 bean. Similar calculations show that larvae caught 

 off the coast of South Carolina would have hatched 

 just south of the Florida Keys, while the larger lar- 

 vae could conceivably have come from as far away 

 as the eastern Caribbean. 



Such back calculations are only approximations 

 since they assume uniform movement of water 

 masses and passive drift by the larvae. However, 

 even very young swordfish are active swimmers 

 and no allowance can be made in the calculations 

 for any active movement by the larvae. 



There are probably two distinct spawning areas 



farther east, one southeast of Barbados, and the 

 other in the Virgin Islands-Southern Sargasso Sea 

 region. 



Spawning probably begins sometime early in the 

 year southeast of Barbados. By March, young lar- 

 vae would have drifted into the Barbados area, and 

 west of the Lesser Antilles. This would account for 

 the sudden occurrence of 30 mm larvae in late 

 March, despite the absence of larvae in these areas 

 earlier in the year. The patchiness of the distribu- 

 tion west of the Antilles could be due to interfer- 

 ence patterns produced by currents flowing be- 

 tween the scattered Windward Islands. Larvae car- 

 ried by these currents would tend to collect at the 

 "nodes" of the pattern. 



Taning (1955) sampled the Virgin Islands- 

 Sargasso Sea region year round, although his efforts 

 during July to September were minimal. Consider- 

 ing only those months with more than 100 h of fish- 

 ing, he found that the largest catches were in Feb- 

 ruary. March, and April. Although our cruises ac- 

 cumulated only 70 h total fishing in this area during 

 the months of January, February, and March, lar- 

 vae were caught in all of these times, with peak 



257 



