Nixon and Jones: Age and growth of larval and juvenile Micropogonias undulatus 
779 
early-spawned juveniles were significantly 
larger (18%) than late-spawned juveniles when 
mean size was adjusted by age (ANCOVA, 
PcO.OOl, Table 2B). 
A Laird-Gompertz growth model fitted the 
entire range of Virginia data well (r 2 =0.95), al- 
though variance in size increased with age 
(Fig. 5). Standard length at hatching (SL (0) ) es- 
timated from the Laird-Gompertz growth model 
(Fig. 5) was 2.7 ±0.3 mm SL and was similar to 
size-at-hatching estimates for laboratory- 
spawned Atlantic croaker from the Chesapeake 
Bay (2.0 mm SL; Middaugh and Yoakum, 1974) 
and North Carolina (2.4 mm SL; Jones 3 ), but 
considerably higher than Warlen’s (1982) esti- 
mate of 0.9 mm SL for wild-captured Atlantic 
croaker larvae from North Carolina. The rate 
of exponential decay of the specific growth rate 
(a) was estimated at 0.0081 ± 0.0012 (Fig. 6). 
Changes in age-specific growth (A t , a function 
of the rate of exponential decay of specific 
growth in time) indicated that larvae experi- 
enced a decline of daily growth rate from 3.2% 
at day 20 to 2.3% by day 60 (Fig. 6). 
Standard length and otolith maximum 
diameter (OMD) relation 
The relation between sagittal OMD and SL was 
best described by a fourth order polynomial (Fig. 
7). A simple linear model also described the 
OMD and SL relation fairly well (SL = 13.5 
(OMD) + 4.2, r 2 =0.98); however, there were 
strong patterns in the residuals. Otolith growth 
was similar between early-captured (fast grow- 
ers captured from September to October) and 
late-captured (slow growers captured from No- 
vember to March) groups when compared by 
slope (P= 0.50). However, a significant difference 
was observed between the two groups when 
otolith size was adjusted for fish size (ANCOVA, 
P<0.001, Table 3A). Size-adjusted means indi- 
cated that otoliths from the early-captured 
group were almost 13% larger than otoliths from 
the late-captured group (Table 3B). Plots of in- 
dividual otoliths showed very little overlap be- 
tween groups (Fig. 8). 
Discussion 
Otolith analysis 
We were unable to obtain known-age Atlantic 
croaker to validate the assumption that incre- 
Larvae 
Juveniles 
40 60 80 100 120 140 160 
Age (days) 
Figure 4 
(A) Growth comparison between early- (September through Oc- 
tober, r 2 = 0.78, n=199) and late-captured (November through 
March, r 2 = 0.77, n=132) Atlantic croaker <15 mm standard length 
(SL) and <80 d. (B) Growth comparison between early- (July 
through August, r 2 =0.92, n=77) and late-spawned (September 
through February, r 2 =0.84, n =314) Atlantic croaker up to 19 mm 
SL. (C) Growth comparison between early- (r 2 =0.92, n= 71) and 
late-spawned (r 2 =0.86, n = 143) Atlantic croaker from 19.1 to 65 
mm SL and from 51 to 142 d. 
3 Jones, C. J. 1995. Applied Marine Research Laboratory, Old 
Dominion University, Norfolk, VA 23529. Unpubl. data. 
