Winner et al.: Age and growth of Archosargus probatocephalus in Tampa Bay, Florida 
159 
Table 2 
Length-length and length-weight regressions for sheepshead (Archosargus pro¬ 
batocephalus) collected in Tampa Bay, Florida, 1993-2009. Measurements include 
standard length (SL) in millimeters, fork length (FL) in millimeters, total length 
(TL) in millimeters, and total weight (WT) in grams. Values in parentheses are 
standard errors. Sex-specific length—weight regressions were necessary because 
male and female regressions had significantly different intercepts. r2=coefficient 
of determination. 
r = 
a + bX 
F 
X 
n 
a 
b 
r2 
TL 
FL 
2218 
0.853 
(0.491) 
1.094 
(0.002) 
0.995 
TL 
SL 
2344 
12.676 
(0.742) 
1.215 
(0.003) 
0.988 
FL 
TL 
2218 
0.621 
(0.448) 
0.910 
(0.001) 
0.995 
FL 
SL 
2218 
11.318 
(0.629) 
1.109 
(0.002) 
0.990 
SL 
FL 
2218 
-7.559 
(0.582) 
0.893 
(0.002) 
0.990 
SL 
TL 
2344 
-7.178 
(0.627) 
0.813 
(0.002) 
0.988 
Logio(WT), females 
Logio (FL) 
1406 
-4.508 
(0.031) 
2.960 
(0.013) 
0.976 
Logio(WT), males 
Logio (FL) 
792 
-4.367 
(0.038) 
2.899 
(0.015) 
0.978 
weight regressions were necessary because regressions 
for males and females had significantly different inter¬ 
cepts (ANCOVA: F=32.15; df=l, 2196; P<0.001), but 
was high for both males (>0.978) and females (>0.976) 
(Table 2). 
Age determination and validation 
Marginal-increment analysis of otoliths from sheeps¬ 
head, with all age classes pooled, indicated that a 
single opaque ring formed annually between May and 
June (Fig. 3). Median marginal increment reached a 
consistent minimum from late spring to early summer 
(May 1995, June 1996, June 1997, June 1998) and a 
consistent maximum during winter (February 1995, 
January 1996, February 1997, January 1998). Large 
interquartile ranges in the months before and during 
opaque-ring deposition indicated that many individu¬ 
als had either just deposited (and therefore had a low 
increm.ent width) or were about to deposit an opaque 
ring (and had a high increment width). Pooling month¬ 
ly marginal increments across all years for individual 
age classes (ages 1-6) also indicated that for each age 
class a single opaque ring was deposited during the 
late spring or summer (Fig. 4). 
Otoliths of 2549 sheepshead were examined for 
age; 154 (6.0%) were excluded from the aging analy¬ 
sis (because there was no agreement among readers 
or because an otolith was damaged), and 169 (6.6%) 
were excluded from sex-specific age analyses (because 
no sex data were available). The male to female sex 
ratio for the sheepshead retained in the aging analy¬ 
sis (1:1.79) did not differ significantly from that of the 
overall sample (1:1.75; G-test: 0.340, df=l, P>0.05). 
But the male-to-female sex ratio for sheepshead ex¬ 
cluded from the aging analysis (1:1.20) was signifi¬ 
cantly different from that of sheepshead retained in 
the aging analyses (G-test: 5.06, df=l, P<0.05). Sex- 
specific length-frequency distributions of fish exclud¬ 
ed from the analysis did not differ significantly from 
those retained (Fig. 2; KS test: females, 0.084, P>0.05; 
males, 0.102, P>0.05). 
