76 
Fishery Bulletin 108(1) 
Table 4 
Von Bertalanffy growth parameters for dusky rockfish 
( Sebastes variabilis) calculated from National Marine 
Fisheries Service, Gulf of Alaska groundfish survey 
data and the central Gulf of Alaska maturity study 
data. L„=mean asymptotic length at maximum age; k = 
growth constant; f 0 =age of fish at zero length; n=number 
of samples. 
L 
x (mm) 
k 
*0 
n 
Gulf of Alaska groundfish 
survey (1996-2003) 
Females 
480 
0.211 
1.106 
752 
Males 
461 
0.243 
1.232 
698 
Sexes combined 
472 
0.223 
1.117 
1450 
Gulf of Alaska maturity 
study (2000-01) 
Females 
449 
0.219 
0.855 
190 
oocyte development in March, followed by a decrease 
in the I G with the onset of parturition occurring from 
April through June. This pattern of increasing I G until 
release of the developed larvae at parturition occurs 
in other rockfish species. The highest I G values for S. 
thompsoni were recorded in March and a corresponding 
increase in the frequency of gestation (fertilized ova). 
Subsequently lower I G values occurred in April and May 
because of an increased frequency of parturition during 
those months (Lee et al., 1998). 
Previous research on dusky rockfish growth in the 
Gulf of Alaska (GOA) has revealed no differences be- 
tween sexes or management regions. Reuter (1999) es- 
Table 5 
Estimated weight-length parameters for dusky rockfish 
( Sebastes variabilis) captured in the National Marine 
Fisheries Service, Gulf of Alaska groundfish surveys 
and the central Gulf of Alaska maturity study. a=scaling 
constant; b=allometric growth parameter; «=number of 
samples. 
Weight-length 
constants 
a b 
n 
Gulf of Alaska combined sex 
from NMFS groundfish 
surveys (1996-2003) 
0.0088 3.11 
1581 
Gulf of Alaska females 
(1996-2003) 
0.0100 3.09 
817 
Maturity study females 
(2000-01) 
0.0131 3.04 
176 
timated growth parameters of dusky rockfish from the 
combined 1990-96 NMFS GOAS and commercial fish- 
eries data and found no differences in growth between 
the three management regions, eastern GOA, central 
GOS, and western GOA, and no difference in growth 
between sexes with values of L 00 = 457 mm, £ = 0.22, 
£ 0 =0.74 for males, and females ofL 00 = 461 mm, £ = 0.25, 
t 0 =1.24. However, the results of the present study in- 
dicate significant differences between male and female 
growth parameters estimated from the fishery-indepen- 
dent data collected on the NMFS GOAS. 
It is not unusual for female rockfish to grow larger 
than males but at a slower rate, because of the trad- 
eoff between somatic growth and 
growth for reproduction (Helser 
et al., 2007). The differences in 
growth parameters between previ- 
ous research and this study could 
be due to the combination of dark 
and dusky rockfish species in the 
commercial fishing data or due to 
the NMFS GOAS data, which were 
collected before 1996. Before 1996, 
the light and dark color variant of 
dusky rockfish caught on the NMFS 
GOAS were combined into a single 
species group as dusky rockfish and 
this treatment prevents comparison 
of dusky rockfish growth param- 
eters before 1996. Differences in 
von Bertalanffy growth parameters 
and the weight-length relationship 
between the NMFS GOAS and the 
maturity-estimate collection in 
this study could be due to the tim- 
ing of the sample collection. The 
NMFS GOAS occurs in the months 
of June and July whereas samples 
Figure 4 
Mean monthly gonadosomatic indices for female dusky rockfish ( Sebastes 
variabilis) captured in the central Gulf of Alaska (n = 124). Sample sizes are 
shown above each column; bars indicate 5% confidence intervals. 
