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Fishery Bulletin 101(4) 



at night, but Bartlett and Haedrich (1968) indicated the 

 reverse. Large swordfish larvae are caught during the day 

 and night in the neuston. The restricted diets of both large 

 and small larvae implies little vertical movement. 



The overall modal increase in larval age from the Gulf of 

 Mexico to the north indicates that spawning takes place in 

 the north-central Gulf of Mexico and off the southeast coast 

 of the United States and that there is possible northward 

 transport. Estimated ages, along with velocities and trajec- 

 tories of currents, indicate that larvae could be transported 

 from considerable distances, but only if they remain within 

 the axes of major currents. The smallest larva collected off 

 the Carolinas was 3.9 mm PSL and had an estimated age 

 of 7 d AFH (this specimen was previously reported as be- 

 ing approximately 4 days old in Govoni et al. [2000]). With 

 3 days incubation at 25°C added to this estimated age, a 

 swordfish egg and larva would be planktonic for 10 days. 

 With a mean axial trajectory and velocity of the Florida 

 Current and Gulf Stream of 1.5 m/s (Olson et al., 1994), a 

 larva 3.9 mm PSL could be transported from as far away 

 as 910 km, which could place the origin of this larva in the 

 Straits of Florida, if its northward progress had not been 

 checked by eddies so typical of the Gulf Loop Current (Maul 

 and Vukovich, 1993) and Gulf Stream, particularly after 

 the Gulf Stream exits the Straits of Florida (e.g. Lee et al., 

 1991; Govoni and Hare, 2001). Off the southeast coast of 

 the United States, swordfish larvae aggregate in the west- 

 ern Gulf Stream frontal zone (Govoni et al., 2000), where 

 northward current velocities are considerably slower than 

 1.5 m/s (Marmorino et al., 1999). Because larvae reside 

 primarily in the western Gulf Stream frontal zone where 

 northward velocities are slower and where the front itself 

 is so frequently distorted by meanders and eddies, it is 

 unlikely, but not impossible, that a larva as young as 7 d 

 APH collected off the Carolinas of the United States could 

 have been transported from the Straits of Florida. 



The largest and oldest larva examined, one collected off 

 South Carolina (Govoni and Hare, 2001), was 115 mm PSL 

 and had an estimated age of 30 d AFH; with 3 days incuba- 

 tion this fish could have been at large for 33 days and would 

 have traveled 4290 km, given the mean axial trajectories 

 and velocities of the Caribbean Sea (-0.2 m/s) and the 

 Yucatan, Gulf Loop, and Florida Currents (-1.5 m/s). This 

 calculation might place the spawning origin of this larva 

 in the eastern Caribbean Sea or south of the Sargasso Sea 

 if a direct, unchecked passage is assumed. 



Inference of the seasonality and geography of spawn- 

 ing is limited and biased by the unsystematic temporal 

 and spatial distribution of the present collections of larval 

 swordfish and by uncertainties about the rate and trajec- 

 tory of transport of eggs and larvae. Yet, taken as a whole, 

 spawning dates, back-calculated from larvae collected in 

 various regions of the western North Atlantic, and the 

 abundance and spatial distribution of the youngest larvae 

 indicate a spawning distribution with modes in three 

 seasons and five regions. The western Gulf Stream frontal 

 zone is the focus of spawning off the southeastern coast of 

 the United States. Spawning in the Gulf of Mexico seems 

 to be focused in the vicinity of the northern most arc of the 

 Gulf Loop Current. 



Estimated spawning dates and the spatial distribution 

 of young larvae offer an alternative to gonad condition and 

 oocyte status as a means of resolving spawning season and 

 location. Spawning season and location resolved in the 

 present study corroborate the scenario recently proposed 

 by Arocha (1997). Rather than the single breeding unit cur- 

 rently recognized for the western North Atlantic by ICCAT, 

 Chow and Takeyama (2000) and Arata ( 1997) proposed two 

 spawning groups: one south of the Sargasso Sea and east 

 of the Lesser Antilles, and the other in the Windward Pas- 

 sage of the Antilles, the Yucatan Channel, and the Straits 

 of Florida up to 35°N latitude. Accordingly, spawning begins 

 in December south of the Sargasso Sea. Larvae from this 

 spawning group transit into the Caribbean, are retained 

 there by its anticyclonic circulation, and use the southeast- 

 em Caribbean as a nursery area. Arocha (1997) implied that 

 the second group spawns progressively later in the year and 

 that larvae are transported with the Gulf Loop and Florida 

 Currents, and the Gulf Stream. Arocha (1997) speculated 

 that larvae and juveniles use the Gulf of Mexico and waters 

 inshore of the Gulf Stream as a nursery area. Spawning 

 dates and abundances of young larvae corroborate Arocha's 

 (1997) proposed scenario for the seasonality and location 

 of spawning and confirm spawning off the southeastern 

 United States in the late spring and summer in the north- 

 ern hermisphere. Spawning dates and abundance of young 

 larvae also indicate the Gulf of Mexico as a nursery area. 

 Further, large numbers of juveniles discarded from the long- 

 line fishery prosecuted in the vicinity of the Charleston Gyre 

 (Cramer, 2001) and the collection of larvae there (Govoni 

 and Hare, 2001) indicate that the waters off the southeast- 

 ern coast of the United States serve as a nursery area. 



Swordfish larvae are collected elsewhere in the western 

 North Atlantic, although they are rarely caught north of 

 Cape Hatteras, North Carolina (Tibbo and Lauzier, 1969). 

 The trajectory of the Gulf Stream north of Cape Hatteras 

 is convoluted and its velocity is slower, ~1 m/s (e.g. Bow- 

 ers and Rossby, 1989; Flierl and Davis, 1993; Hare et al., 

 2002); the transit period of plankton from Cape Hatteras 

 to the Azores is 120-300 days (Scheltema, 1971). Swordfish 

 spawned in the western North Atlantic would be juvenile 

 fish by the time they reached the eastern North Atlantic. 

 North of Cape Hatteras, the Gulf Stream sheds eddies into 

 the Sargasso Sea (McGuillicuddy et al., 1998); thus, the 

 general location for juvenile swordfish that are spawned 

 and not retained in the western North Atlantic may well 

 be the central Atlantic and Sargasso Sea. 



Swordfish are multiple spawners (Arocha, 2002) and 

 adults may move and spawn among regions of the western 

 North Atlantic. Movement of spawning adults, along with 

 transport of larvae, may result in the genetically well-mixed 

 population of the western North Atlantic ( Alvarado Bremer 

 et al., 1995a). There is apparently no genetic exchange be- 

 tween northwestern Atlantic and Mediterranean reproduc- 

 tive populations (Alvarado Bremmer et al., 1995b; Chow 

 and Takeyama, 2000). Transoceanic migration of adult fish 

 is possible, but cross-Atlantic transfer of swordfish larvae 

 is not likely. Swordfish lars'ae, collected principally in water 

 >25°C (Govoni et al., 2000), probably perish as Gulf Stream 

 water cools when it traverses the northern western North 



