Peters and Schmidt: Age and growth of larval and early juvenile Scomberomorus maculatus 
537 
migrations, which are often strongly associated with 
light cycles, serve to increase daily increment defi- 
nition (Campana and Neilson, 1985). 
Other species of scombrid larvae and early juve- 
niles ( E . pelamis, T. albacares, E. alletteratus, Auxis 
thazard, and Scomber scombrus) are known to un- 
dergo vertical diel migration feeding primarily at the 
surface at night (Matsumoto, 1958; Grave, 1981). 
Collins and Stender (1987) found statistical evidence 
for vertical migration to the surface at night in both 
S. maculatus and S. cavalla. Spanish mackerel and 
other species of Scomberomorus are known to feed 
on ichthyoplankton during the larval stage and are 
almost completely piscivorous as juveniles (Naughton 
and Saloman, 1981; Jenkins et al., 1984). The large 
eyes of scombrids, even during the larval stage, sug- 
gest that they are visual predators. Therefore, light 
cycles probably have a strong influence on prey de- 
tection. Moreover, feeding opportunities related to 
diurnal vertical migrations of prey organisms, along 
with fluctuations in temperature associated with diel 
vertical migrations, may further serve to entrain this 
endogenous rhythm of calcium carbonate deposition. 
Age and growth 
Marginal increment analysis indicated that otolith 
increments are deposited daily in larvae and juve- 
niles from 7 to 95 mm SL. However, because we were 
unsuccessful at capturing preflexion larvae, it was 
impossible to determine if increment counts truly 
reflected age from fertilization. Very little informa- 
tion is available on otolith formation in scombrids, 
although otoliths are among the first calcified struc- 
tures and are present in scombrid embryonic stages 
(Matsumoto, 1958; Radtke, 1983; Brothers et ah, 
1983). In E. pelamis larvae reared from hatching 
(Radtke, 1983), the core region of the otolith (the 
primordium and two diffuse increments), along with 
the pattern of subsequent increment formation, is 
very similar in appearance to otoliths of S. maculatus 
(Fig. 3). Radtke (1983) observed that the two core 
increments were present at hatching. 
The two core increments in S. maculatus , because 
of their atypical pattern of deposition, are likely to 
have been formed during the egg stage or prior to 
yolk-sac absorption. However, it is not known 
whether these increments are deposited daily. Be- 
cause hatching and yolk-sac absorption of Spanish 
mackerel larvae usually occurs five days after fer- 
tilization at temperatures experienced during the 
spawning season in South Carolina waters (Berrien 
and Finan, 1977; Fritzche, 1978), errors in age esti- 
mation are likely to be consistent among most fish, and 
growth rate calculations would remain unaffected. 
Considerable variation was observed in the growth 
rates of individual fish, particularly among juveniles 
older than 23 days. The use of specimens collected 
over a wide spatial and temporal range was prob- 
ably responsible for much of this variation. However, 
the overall predicted mean absolute growth rate of 
2.4 mm/d ay is within the range of growth rates ob- 
served in other scombrids during the first few months 
of life (1 mm/day-6 mm/day) (see Brothers et al., 
1983, for review). The regression lines estimating the 
relationship between age and length appeared to be 
a good approximation (r 2 =0.97, P<0.0001) of growth 
in young Spanish mackerel. 
Acknowledgments 
We would like to express sincere thanks to Mark 
Collins, Robert Johnson, George Sedberry, and Bruce 
Stender for their assistance and advice. For their 
assistance in field sampling we would like to thank 
Shirelle Brown, Scott Van Sant, Byron White, Paula 
Keener-Chavis, Pete Richards, and Vince Taylor. We 
would also like to thank Bruce Stender, Charles 
Barans, William Roumillat, and SEAMAP for pro- 
viding many of the specimens used in this study. Fi- 
nancial support and equipment for this study were 
provided by the South Carolina Department of Natu- 
ral Resources, the University of Charleston’s Grice 
Marine Laboratory, and the Slocum-Lunz Foundation. 
Literature cited 
Berrien, P., and D. Finan. 
1977. Biological and fisheries data on Spanish mackerel, 
Scomberomorus maculatus (Mitchill). U.S. Dep. Commer., 
NOAA/NMFS Sandy Hook Lab. Tech. Ser. Rep. 9, 58 p. 
Brothers, E. B. 
1987. Methodological approaches to the examination of 
otoliths in ageing studies. In R. C. Summerfelt and G. E. 
Hall (eds.), The age and growth of fishes, p. 319-330. Iowa 
State University Press, Ames, Iowa. 
Brothers, E. B., and W. N. MacFarland. 
1981. Correlations between otolith microstructure, growth, 
and life history transitions in newly recruited french grunts 
[Haemulon flavolineatum (Desmarest), Haemulidae]. In 
R. Lasker and K. Sherman (eds.), The early life history of 
fish: recent studies, p. 369-374. ICES Mar. Sci. Symp., 
Woods Hole. 
Brothers, E. B., E. D. Prince, and D. W. Lee. 
1983. Age and growth of young-of-the-year bluefin tuna, 
Thunnus thynnus, from otolith microstructure. In E. D. 
Prince and L. M. Pulos (eds ), Proceedings of the interna- 
tional workshop on age determination of oceanic pelagic 
fishes: tunas, billfishes, and sharks, p. 49-59. U.S. Dep. 
Commer., NOAATech. Rep. NMFS 8. 
Campana, S. E. 
1984. Interactive effects of age and environmental modifi- 
