HALES: ROUND SCAD IN THE SOUTH ATLANTIC BIGHT 



Growth rates reported in this study for juvenile 

 round scad are similar to those of juvenile Selar 

 crumenopthalmus (Kawamoto 1973) and Trachurus 

 trachurus (Macer 1977), and would enable spring- 

 spawned round scad encountering favorable condi- 

 tions to spawn in the fall (Leak 1981). Other species 

 of Decapterus are reported to grow more slowly 

 (Yamaguchi 1953; Tiews et al. 1970; Ingles and 

 Pauly 1984), but such studies used length-frequency 

 information only and may have underestimated 

 growth. These species {D. pinnulatus, D. russelli, 

 D. macrosoma) reach sexual maturity at 17-20 cm 

 FL in their first or second year, and attain 25-35 

 cm FL in 3-5 years (Yamaguchi 1953, Tiews et al. 

 1970). The rapid growth of round scad to sexual 

 maturity suggests that this species is under strong 

 selection to mature early. Mortality estimates for 

 round scad (Leak 1981; Houde et al. 1983) are high 

 even in comparison with other coastal pelagic fishes, 

 which do not achieve as large a size as round scad 

 during their first year. 



Daily growth increments were easily distinguished 

 in juveniles and small adults, but could not be used 

 to determine ages of most adults. Frequent spawn- 

 ing involving the high energetic expenditures 

 reported for other pelagic fishes (Hubbs 1976; 

 DeMartini and Fountain 1981) would result in slow 

 growth of adults. Specific growth rates based on 

 Houde et al. (1983) (0.04% FL d'^ for 1-2 yr olds, 

 and 0.03% FL d"^ for 2-3 yr olds) are much slower 

 than the rate of young adults (0.28% FL d'^) 

 observed in this study. A reduction in increment 

 thickness with growth (Brothers 1979; Campana 

 1985) might result in the exceedingly fine incre- 

 ments observed in the outer portions of the otoliths 

 of adults. Another possibility is that growth of adults 

 is insufficient to maintain the pattern of daily incre- 

 ment formation. McGurk (1984) has reported that 

 daily increment formation in larval Clupea harengus 

 may be altered when absolute growth rates are 

 <0.36 mm d'^. 



Occurrence of growth interruptions in the outer 

 portions of otoliths of most adults also hindered age 

 determination. The period of formation of such 

 marks was not known. If such marks are not formed 

 in 1 day, then inclusion of such marks as daily in- 

 crements would result in underestimation of the 

 ages of adults. Growth interruptions may result 

 from spawning (Panella 1974), lunar or tidal 

 rhythms (Rosenberg 1982), or stress (Ralston and 

 Miyamato 1983); however, correlations between 

 such events and the growth record of round scad 

 could not be determined. 



ACKNOWLEDGMENTS 



I thank W. D. Anderson, Jr., C. A. Barans, C. K. 

 Biernbaum, N. A. Chamberlain, and C. A. Wenner 

 for advice and encouragement, and D. E. Facey, G. 

 S. Helfman, G. R. Sedberry, W. A. Roumillat, and 

 the anonymous reviewers for their comments on 

 various drafts. Personnel of the BLM (contract 

 AA551-CT9-27) and MARMAP (contract NA84- 

 WCC-06101) programs at the Marine Resources 

 Research Institute, Charleston, SC provided much 

 needed specimens and assistance. K. Swanson, J. 

 Lay, E. Peters, B. Sanders, and J. Barrett prepared 

 the figures, and J. Evans typed the manuscript. K. 

 Piatt provided invaluable assistance throughout the 

 course of this study. Financial support from the 

 Department of Biology at The College of Charles- 

 ton, the Charleston Higher Education Consortium, 

 the Slocum-Lunz Foundation and Sea Grant 

 #NA80AA-0091 to G. Helfman is gratefully ac- 

 knowledged. Portions of this manuscript were taken 

 from a thesis submitted in partial fulfillment of the 

 requirements for the M.S. degree. This is contribu- 

 tion No. 222 from the Marine Resources Research 

 Institute and No. 71 from the Grice Marine Bio- 

 logical Laboratory. 



LITERATURE CITED 



Akaoka, T. 



1971. The purse seine fishery in Japan, /n H. Kristjonsson 

 (editor), Modern fishing gear of the world. Vol. Ill, p. 161- 

 163. Fishing News Ltd., Lend. 

 Allen, L. G., and E. E. DeMartinl 



1983. Temporal and spatial patterns of nearshore distribu- 

 tion and abundance of the pelagic fishes off San Onofre- 

 Oceanside, California. Fish. Bull., U.S. 81:569-586. 

 Aprieto, V. L. 



1974. Early development of five carangid fishes in the Gulf 

 of Mexico and the south Atlantic coast of the United States. 

 Fish. Bull., U.S. 72:415-444. 

 Atkinson, L. P., T. N. Lee, J. 0. Blanton, and W. S. Chandler. 

 1983. Climatology of the southeastern United States con- 

 tinental shelf waters. J. Geophys. Res. 88:4705-4718. 

 Bagenal, T. B., and E. Braum. 



1978. Eggs and early life history. In T. B. Bagenal (editor), 

 Methods for assessment of fish production in fresh waters, 

 p. 165-201. Blackwell Sci. Publ., Lend. 

 Berry, F. H. 



1968. A new species of carangid fish (Decapterus tabl ) from 

 the western Atlantic. Contrib. Mar. Sci. 13:145-167. 

 Blanton, J. 0., L. P. Atkinson, L. J. Pietrafesa, and T. N. 

 Lee. 



1981. The intrusion of Gulf Stream water across the continen- 

 tal shelf due to topographically induced upwelling. Deep- 

 Sea Res. 28:393-405. 



Blaxter, J. H. S., and J. R. Hunter. 



1982. The biology of clupeoid fishes. Adv. Mar. Biol, Acad. 

 Press, N.Y., 20:1-224. 



265 



