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Fishery Bulletin 96(3), 1 998 
1990 (23.0 kg) were slightly heavier ( ANOVA, F= 4.67, 
P<0.05) than those landed in 1991 (21.4) and 1992 
(22.3 kg). Again, the difference among years is only 
7% of average total weight. 
Comparisons between areas and gears 
Black drum collected in Chesapeake Bay and coastal 
waters did not differ in simple biological attributes. 
Catches from the two areas showed no significant 
differences in age (bay=25.8 yr, coastal=26.8 yr, Z=- 
1.21, P>0.05), total weight (bay=21.7 kg, coastal=22.4 
kg, Z=-1.32, P>0.05), or total length (bay=109.5 cm, 
coastal=109.5 cm, Z=0.09, P>0.05). Hence, data from 
both areas were pooled in all other analyses. 
Recreational and commercial catches showed sta- 
tistically significant differences in total length 
(Z=2.13, P<0.05), but not in total weight (commer- 
cial=22.1 kg, recreational=22.2 kg, Z=0.76, P>0.05), 
or age (commercial=26.3 yr, recreational=26.9 yr, 
Z=1.60, P>0.05). Mean TL of the commercial catch 
was 109.0 cm (n=698, SE=8.7 cm), and recreational 
mean TL was 110.4 cm (n=166, SE=8.6 cm). Mean, 
median, ranges, and quantile measures of TL are 
almost identical for these two fisheries. Although the 
differences in TL are statistically significant because 
of large sample size, they are not biologically mean- 
ingful. Hence, data from these fisheries were pooled 
to analyze growth and mortality. 
Growth 
Observed lengths varied greatly within age (Fig. 2). 
Growth was rapid before 15 years of age but slowed 
by age 20. Lengths thereafter varied asymptotically 
about the mean. Black drum have achieved 58% of 
L to , by age 6, when fish are first caught in the bay, 
and have achieved 90% by age 20, after which they 
are fully recruited to the gears. Apparently growth 
was very rapid in the first 5 years, ages absent from 
our collections. The VBGF equation for data pooled 
over the period 1990-92 is 
L t = 117.3(l- e“ 0105u+2 - 3) ). 
No differences were found in growth curve param- 
eters in length between the sexes (P>0.05) or years 
(P>0.05 ). We observed large numbers of fish at older 
age, permitting a good estimate for L x ( zz =87 1 ; in- 
cludes juveniles, r 2 =0.998). However, because we 
observed no fish between 1 and 5 years, our estimate 
of K is not optimum. Parameters estimated and 
asymptotic standard errors are given in Table 1. 
Observed weights of Chesapeake Bay black drum 
varied greatly within age (Fig. 3). As with age-length 
Table 1 
Summary of parameter estimates for the von Bertalanffy growth 
equation on total length (cm) and total weight (kg) of Chesa- 
peake Bay region black drum, Pogonias cromis (199092). 
95% confidence 
intervals 
Parameter 
Estimate 
SE 
Lower 
Upper 
117.3 
0.4 
116.5 
118.1 
K 
0.105 
0.003 
0.099 
0.111 
t 0 
-2.3 
0.2 
-2.7 
-1.9 
37.4 
1.7 
34.0 
40.8 
K' 
0.033 
0.003 
0.027 
0.039 
t 0 
-1.5 
0.9 
-3.3 
0.3 
data, growth was rapid for the first 6 years. Although 
it slowed thereafter, fish still grew appreciably in 
weight until growth slowed substantially at 45 yr. 
Black drum have reached 22% of by age 6 when 
they first appear in the bay as adults, 51% of W ^ by 
age 20, and 78% by age 45. Hence, they grew more 
slowly in weight than in length. The VBGF equation 
for data pooled over the period 1990-92 is 
W t =37.4(l- e -°- 03(i+1 - 5) ). 
We observed large numbers of older fish, permit- 
ting a good estimate for ( n= 586, r 2 =0.977). How- 
ever, because we observed no fish between ages 1 
and 5, our estimate of K' is not optimum. Para- 
meters estimated, asymptotic standard errors, and 
95% confidence intervals are given in Table 1. 
No differences were found in weight-growth curve 
parameters between the sexes (P>0.05). However, 
pairwise comparisons showed parameters differed 
between the years 1990 and 1991 (1990: 17^=57.2 kg, 
fG=0.0 18/yr, P 0 =-2.24 yr; 1991: W m = 29.8 kg, 
-K^O-052/yr, P 0 =0.06 yr, likelihood ratio test: % 2 = 
10.54, P< 0.05). Fish captured in 1991 weighed less 
at older ages than in 1990 and 1992. We have no 
explanation for this; causes could be minor, i.e. sam- 
pling error, a slightly greater proportion of older fish 
that had completed spawning in 1992, or perhaps 
fish that were in worse condition in 1991. 
A pooled length-weight regression was developed 
(Fig. 8) with the equation 
TW = 1.01 X 10" 2 TL 311 (r 2 = 0.97; n=599; PcO.Ol). 
The slope of the regression line (6=3.11; SE=0.03) 
was significantly different from 3.00 (Gtest; t= 3.75; 
P<0.05), indicating allometric growth. 
