Chilton: Maturity and growth of Sebastes variabilis in the central Gulf of Alaska 
75 
(Fig. 5A). The likelihood ratio test 
showed a significant difference in 
growth parameters between the fe- 
male dusky rockfish caught in the 
maturity study and females from 
the NMFS GOAS (x 2 =158.8, df =3, 
P<0.001) (Table 4). 
Von Bertalanffy growth para- 
meters for male dusky rockfish 
from the NMFS GOAS were 
L 30 =461 mm, £ = 0.243, and f 0 =1.232 
compared to values of L 00 =480 mm, 
£ = 0.211, and f 0 =1.106 for females; 
these results indicate that fe- 
male dusky rockfish have a slower 
growth rate but a larger mean 
asymptotic length than males 
(Fig. 5B). The likelihood ratio test 
showed a significant difference 
between male and female dusky 
rockfish (% 2 = 61.5, df=3, P<0.001) 
from the NMFS GOAS (Table 4). 
There was a significant differ- 
ence detected in the slopes of the 
log-transformed weight-length da- 
ta derived from the female dusky 
rockfish maturity sample when 
compared to female dusky rockfish 
caught in the NMFS GOAS accord- 
ing to the Student’s f-test (t=4.94, P<0.005) (Table 5). 
Although the slope of the weight-length data from the 
maturity study was significantly different from the 
NMFS GOAS, both data sets had comparable length 
ranges with 190 to 500 mm FL for the maturity study 
and 170 to 530 mm FL for the NMFS GOAS. Conse- 
quently, this difference is not likely due to trawl gear 
selectivity in the NMFS GOAS. 
Discussion 
The maturity parameters presented in this study are not 
consistent with previously reported estimates of size and 
age at 50% maturity for female dusky rockfish of 11.3 
years and 428 mm (Love et al., 2001), which are higher 
and larger than the results from the present study. The 
differences could be due to the timing, sample size, and 
method of determining the previous maturity estimates, 
where ovary development was evaluated at a macroscopic 
level from a small number of samples. The results of 
this study are based on a larger sample, collected over 
multiple months during a two-year period, and on an 
improved method to evaluate ovary development and 
may therefore represent a better estimate of maturity. 
The seasonal timing of parturition in dusky rockfish 
is comparable to that of other Gulf of Alaska rockfish 
species, in April and May (Love et al., 2001; Chilton, 
2006). Parturition begins to occur in female northern 
rockfish from the central Gulf of Alaska in April and 
higher numbers of POFs are found in May and June 
TabSe 3 
Maturity parameters and variances for female dusky rock- 
fish ( Sebastes variabilis) in the central Gulf of Alaska esti- 
mated by fitting a logistic function to the maturity data as 
a function of age or length with generalized linear model- 
ing. a=scaling constant; b=allometric growth parameter. 
Value 
Variance 
^0.5 
365 mm 
38.055 
a 
-12.728 
3.581 
b 
0.035 
2.408 
A).5 
9.2 years 
0.254 
a 
-3.047 
0.528 
b 
0.332 
0.007 
(Chilton, 2006). The small number of samples collected 
for this study in June prevented an estimation of the ex- 
tent of parturition in dusky rockfish beyond the month 
of May. The smaller mature dusky rockfish exhibiting 
stage-7 ovaries in April were most likely fertilized in 
the previous reproductive season which could have oc- 
curred as late as July in the previous year. Nichol and 
Pikitch (1994) found that oocytes of smaller mature 
female darkblotched rockfish developed later in the 
season than oocytes from larger mature females. 
The corresponding increase in female dusky rockfish 
ovary weight compared to total body weight, or gonad- 
osomatic index (/ G ), is a result of the advancement of 
