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285 



Other studies suggest that common dolphin in the 

 tropical Atlantic (Gibbs and Collette, 1959) and 

 Pacific (Aoki and Ueyanagi, 1989) spawn closer to 

 shore than do pompano dolphin. In the Pacific, mid- 

 oceanic occurrences of common dolphin larvae are lim- 

 ited to waters near islands (Aoki and Ueyanagi, 1989). 



Overall, larval common dolphin are significantly 

 more abundant than pompano dolphin in the north- 

 ern Gulf (Table 4; Appendix Fig. 2) and along the 

 southeastern United States (Fahay, 1975; Powles, 

 1981). Larvae of both common dolphin and pompano 

 dolphin were particularly abundant around the 

 Mississippi River delta. Higher larval dolphinfish 

 abundances near the delta may reflect the generally 

 higher abundance of fish larvae in the delta area 

 (Ditty, 1986; Govoni et al., 1989; Grimes and 

 Finucane, 1991) as compared to the open Gulf 

 (Richards et al., 1989), or may reflect greater inten- 

 sity of neuston sampling near the delta rather than 

 the actual distribution of spawning adults. In the 

 Pacific and Indian Oceans, larval pompano dolphin 

 are more abundant than common dolphin 

 (Shcherbachev, 1973; Aoki and Ueyanagi, 1989). 



Dolphinfish may spawn year-round in the Gulf, at 

 least in the southern part of the study area where 

 seasonal water temperatures remain above about 

 24°C. Estimated spawning dates based on collection 

 of preflexion common dolphin support spawning in 

 the northern Gulf from at least April to December 

 (Fig. 4). Peak spawning of common dolphin occurs 

 during spring and early fall based on higher catches 

 of larvae during these seasons, although differences 

 among seasons are not significant. Along the Atlan- 

 tic coast, eggs have been collected during July and 

 August in the Gulf Stream (Hassler and Rainville, 

 1975) and larvae and early juveniles year-round 

 along the southeastern United States (Fahay, 1975; 

 Powles and Stender, 1976) and tropical Atlantic 

 (Gibbs and Collette, 1959). Ripe female common 

 dolphin occur in the Gulf Stream off Cape Hatteras 

 (North Carolina) from at least May through July 

 (Schuck, 1951; Rose, 1966), and in the Florida Cur- 

 rent from November to July (March spawning peak, 

 Beardsley, 1967). Pompano dolphin spawn in the 

 Gulf from spring through at least early fall (Fig. 4; 

 Gibbs and Collette, 1959). If larval pompano dolphin 

 growth rates are similar to those for common dol- 

 phin (about 1 mm/day, Hassler and Rainville, 1975; 

 Uchiyama et al., 1986), the two mid-October col- 

 lected pompano dolphin larvae (18.3 and 22.5 mm) 

 were spawned during late September. Pompano dol- 

 phin spawn year-round in tropical mid-Atlantic and 

 South Atlantic Bight waters based on collection of 

 larvae and juvenile length-frequency data (Potthoff, 

 1971; Fahay, 1975). 



We found no significant diel differences in catch 

 of larvae for either species as did Fahay (1975). Eld- 

 ridge et al. (1977), however, found both common 

 dolphin and pompano dolphin significantly more 

 abundant at night, and that catch of larval common 

 dolphin increased with concentration of Sargassum. 

 Larval common dolphin <10 mm are more common 

 in subsurface (i.e. depths of 20-30 m) than in sur- 

 face tows during both day and night (Aoki and 

 Ueyanagi, 1989). Larval pompano dolphin <10 mm 

 are more frequently collected in subsurface tows 

 during the day only; larvae >10 mm are more com- 

 mon near the surface during the night (Aoki and 

 Ueyanagi, 1989). 



New information on the larval morphology of pom- 

 pano dolphin from this study corroborates Johnson's 

 (1984) hypothesis of a relationship between Cory- 

 phaenidae and Rachycentridae rather than that 

 previously hypothesized between Rachycentridae 

 and Echeneididae. Larvae of dolphinfishes and co- 

 bia share similar patterns of head spination: later- 

 ally swollen pterotics; a single, simple spine on the 

 supraorbital ridge of each frontal bone (except in C. 

 equiselis which may have multiple spines along the 

 ridge); a small posttemporal spine; and both 

 dolphinfish and cobia have 3 or 4 spines along the 

 inner shelf and 4 or 5 spines along the outer shelf 

 of the preopercle with the largest spines on either 

 side of the preopercular angle (Johnson, 1984; Ditty 

 and Shaw, 1992; this study). Dolphinfishes have a 

 small maxillary spine that cobia lack (Ditty and 

 Shaw, 1992; this study), but no spine on the supra- 

 clei thrum found in cobia (Dawson, 1971; Ditty and 

 Shaw, 1992; this study). Echeneis lack head spines. 

 Larval dolphinfishes and cobia also lack large 

 hooked teeth anteriorly on the dentary found in 

 Echeneis (Johnson, 1984; Leis and Trnski, 1989). 

 Dolphinfishes differ from cobia by lacking dorsal and 

 anal spines and by having more vertebrae (30-34 in 

 dolphinfishes versus 25 in cobia). Dolphinfishes also 

 have 50+ soft dorsal rays, whereas cobia have 27- 

 33 (Ditty and Shaw, 1992). 



Acknowledgments 



This study was supported by the Marine Fisheries 

 Initiative (MARFIN) Program (contract numbers: 

 NA90AA-H-MF111 and NA90AA-H-MF727). The 

 authors thank the Southeast Area Monitoring and 

 Assessment Program (SEAMAP) and Gulf States 

 Marine Fisheries Commission for providing speci- 

 mens and environmental data. Bruce Mundy 

 (NMFS, Honolulu Laboratory, Hawaii) provided a 



