Nixon and Jones: Age and growth of larval and juvenile Micropogonias undulatus 
781 
Table 3 
Otolith comparison between faster-growing early-captured 
(September through October) Atlantic croaker and slower- 
growing late-captured (November though March) Atlantic 
croaker between 11 and 37 mm standard length (SL) with 
an analysis of covariance (ANCOVA) of the otolith maxi- 
mum diameter (OMD) of sagittae (mm), with SL of fish (mm) 
as the covariate. Size-adjusted means equals the mean 
OMD of sagittae, adjusted for the effects of SL of fish. 
ANCOVA 
A 
df 
F-value 
P-value 
Covariate standard length 
1 
1,126.9 
P<0.001 
Main effect 
Early-captured vs. 
late-captured 
1 
36.2 
PcO.001 
Residual sums 
of squares (d) 
1.16 (66) 
r 2 
0.95 
B Size adjusted means (mm) (SE) 
Early-captured: 1.54 (0.02) Late-captured: 1.25 (0.02) 
and Judy, 1983; Warlen and Burke, 1990). However, 
only two studies (Warlen, 1982; this study) used daily 
age information from otoliths to support such find- 
ings. Daily age information is critical because size- 
at-age is highly variable in this species, and age- 
based data provide reliable confirmation of cross- 
shelf transport of larvae. Warlen (1982) found a gen- 
eral increase in the age of fish entering the Beaufort 
estuary as the season progressed, and suggested this 
increase in age was an effect of variable transport 
distance or rates to the estuary (or both). Seasonal 
trends observed in this study may be attributed to 
similar processes. 
Mean ages generally increased over time, lagging 
about 10 d between monthly sampling dates, sug- 
gesting constant recruitment over the entire sam- 
pling season. However, mean ages in the rivers de- 
clined after December. Our samples collected in Janu- 
ary along river transects show a gradient of smaller, 
younger individuals upstream and of larger, older 
individuals downstream. Bottom waters in the York 
River experience a winter temperature gradient, with 
the lowest temperatures occurring in upper reaches 
of the river (Chao and Musick, 1977; Dameron et al. 1 ; 
Land et al. 4 ) and the higher temperatures in the Bay 
mainstem. This bottom water temperature gradient 
coupled with the increase in size of Atlantic croaker 
4 Land, M. F., P. J. Geer, C. F. Bonzek, and H. M. Austin. 1994. 
Juvenile finfish and blue crab stock assessment program. Bot- 
3.0 r 
0 0 1 1 1 1 1 1 1 
10 15 20 25 30 35 40 
Standard length (mm) 
Figure 8 
The relation between otolith maximum diameter (OMD) 
(mm) and standard length (SL) of fish (mm) illustrating 
otolith and somatic growth relation between faster-grow- 
ing, early-captured (September through October) Atlantic 
croaker (n=36) and slower-growing, late-captured (Novem- 
ber through March) Atlantic croaker (n=32) between 11 
and 37 mm SL. 
tom trawl survey. Annual data summary report series. Volume 
1988. Spec. Sci. Rep. Va. Inst. Mar. Sci., College of William 
and Mary, Gloucester Point, VA, 171 p. 
