738 
Fishery Bulletin 96(4), 1 998 
ally mature female grouper ranging in length from 
565 to 1310 mm and for 43 sexually mature male 
grouper ranging in length from 947 to 1518 mm as 
GSI = (GW / (TW - GW)) x 100, 
where GW = total gonad weight (g); and 
TW = total fish weight (g). 
We measured the diameters of whole oocytes from 
six females whose ovaries contained numerous hy- 
drated oocytes. Samples of ovarian tissue that were 
preserved in 10% formalin were rinsed briefly in 
water and transferred to 33% glycerin for measure- 
ments. Diameters of at least 300 oocytes for each fe- 
male were measured with a digital image-prossessing 
system. Only oocytes larger than 0.2 mm in diam- 
eter were measured. 
We estimated the length at which 50% of the fe- 
males in the population reached sexual maturity by 
fitting a logistic function to the percentage of females 
that were sexually mature and their respective 
lengths. A similar function was fitted to the percent- 
age of the population made up by females to esti- 
mate the length at which 50% of the females in the 
population transformed into males. The parameter 
b in Table 1 is the inflection point of the logistic curves 
and is the estimate of the length or age at which 50% 
of the females in the population were sexually ma- 
ture or the length or age at which 50% of the popula- 
tion had undergone transition from female to male. 
Sometimes distinguishing between the gonads of sexu- 
ally immature grouper and the regressed gonads of 
mature fish was difficult, and we eliminated 29 females 
that ranged in length from 586 to 894 mm from our 
analysis of maturation because we were uncertain of 
their maturity. Hunter et al. ( 1992) recommended that 
only fish collected early in the spawning season be used 
to estimate the length at 50% maturity, but because 
we found evidence of some spawning during most of 
the year, we included all months in our analysis. 
Results 
The 1166 black grouper we examined ranged from 
155 to 1518 mm in length. Among black grouper that 
we sexed, females ranged from 155 to 1310 mm in 
length (mean=696.3, SD=204.53, t?=834) and males 
ranged from 947 to 1518 mm (mean=1254.9, 
SD=126.19, n=54; Fig. 1). Our sample contained 276 
grouper that were not sexed, usually because the 
grouper had been eviscerated at sea by fishermen. 
The sex ratio of our sample was 1:15.4 (male:female); 
greatly skewed towards females. Black grouper 
Table 1 
The relations between standard length, fork length, and 
total length, between length and weight, between the per- 
centage of females that were sexually mature and length, 
and between the percentage of the population made up by 
females and length of black grouper, Mycteroperca honaci , 
from South Florida waters. TL = total length (mm), FL = 
fork length (mm), SL = standard length (mm), WT = whole 
weight (g), GWT = gutted weight (g), OTOWT = otolith 
weight (g), and AGE = age (years). The total length range 
for all length-length regressions was 238-1518 mm and 
for the length-weight regression was 177-1518 mm; the 
total weight range for the total weight-gutted weight re- 
gression was 467-61,462 g; the age range for the age-otolith 
weight regression was 1-30.5 years. 
Y = a 
+bX 
a 
b 
Y 
X 
n 
(1 SE) 
(1SE) 
r 2 
SL 
FL 
1,134 
-23.712 
0.883 
0.999 
(0.6852) 
(0.0008) 
SL 
TL 
1,141 
-21.611 
0.858 
0.999 
(0.7743) 
(0.0009) 
FL 
SL 
1,134 
27.607 
1.131 
0.999 
(0.7514) 
(0.0011) 
FL 
TL 
1,150 
1.641 
0.973 
0.999 
(0.5223) 
(0.0006) 
TL 
SL 
1,141 
26.186 
1.164 
0.999 
(0.8757) 
(0.0012) 
TL 
FL 
1,150 
-1.317 
1.028 
0.999 
(0.5378) 
(0.0006) 
WT 
GWT 
638 
81.519 
1.056 
0.999 
(12.9253) 
(0.0014) 
log 10 WT 
log 10 TL 
772 
-5.457 
3.218 
0.995 
(0.0323) 
(0.0115) 
Y = a + bx -~[x 
OTOWT 
AGE 
389 
-0.1026 
0.1210 
0.952 
(0.0036) 
(0.0014) 
Y 
= (l/(l + e ( 
a< x- 6)) j j x 100 
% Mature 
TL 
782 
-0.0194 
826.0 
0.592 
(Females) 
(0.0017) 
(4.75) 
% Mature 
AGE 
617 
-1.375 
5.20 
0.555 
(Females) 
(0.1341) 
(0.078) 
% Females 
TL 
888 
0.016 1214.4 
0.618 
(0.0013) 
(5.05) 
% Females 
AGE 
694 
0.355 
15.55 
0.551 
(0.0287) 
(0.382) 
landed in Pinellas County on Florida’s Gulf coast by 
commercial fishermen were much larger than those 
landed in the Florida Keys (Fig. 2). The male:female 
sex ratio of the black grouper we sampled that were 
landed in the Florida Keys was 1:58.7, and the sex 
