70 
Abstract — The dusky rockfish ( Se - 
bastes variabilis) has recently been 
resurrected as a distinct species in 
the genus Sebastes. Reproductive biol- 
ogy and growth were examined for 
this redescribed species in the cen- 
tral Gulf of Alaska. Age and length at 
50% maturity were 9.2 years and 365 
mm fork length, respectively, which 
are lower than previously reported. 
Fertilized ova and eyed embryos 
were observed in April and evidence 
of postparturition was not observed 
until May. The gonadosomatic index 
decreased with the onset of post- 
parturition in May. Von Bertalanffy 
growth parameters for female dusky 
rockfish, estimated from the maturity 
samples, were significantly different 
from growth parameters derived from 
Gulf of Alaska fishery-independent 
survey data. 
Manuscript submitted 6 August 2008. 
Manuscript accepted 26 October 2009. 
Fish. Bull. 108:70-78 (2010). 
The views and opinions expressed 
or implied in this article are those 
of the author (or authors) and do not 
necessarily reflect the position of the 
National Marine Fisheries Service, 
NOAA. 
Maturity and growth of female dusky rockfish 
(Sebastes variabilis) in the central Gulf of Alaska 
Elizabeth A. Chilton 
Email address: elizabeth.chilton@noaa.gov 
National Oceanic and Atmospheric Association 
National Marine Fisheries Service 
Alaska Fisheries Science Center 
Kodiak Laboratory 
301 Research Court 
Kodiak, Alaska 99615 
One quarter of the 65 rockfish species 
distributed throughout the Northeast 
Pacific reside in the Gulf of Alaska 
(Love et al., 2002). Life history infor- 
mation is limited for these temperate 
rockfish species, such as the repro- 
ductive biology and growth rates of 
the female dusky rockfish ( Sebastes 
variabilis ) (Pallas, 1814), which is the 
predominant pelagic rockfish species 
on the central Gulf of Alaska shelf. 
Reproduction in rockfish species is 
viviparous; fertilization of oocytes is 
internal and adult females provide 
some nutritional support for the devel- 
oping larvae until parturition (Boe- 
hlert and Yoklavich, 1984). Length 
at 50% maturity in female rockfish 
is variable, occurring at a larger size 
in more northerly species. Rockfish 
species in the Gulf of Alaska also 
have wide ranging growth rates, with 
pelagic shelf rockfish growing faster 
than their demersal shelf congeners 
(Haldorson and Love, 1991; Munk, 
2001 ). 
Dusky rockfish have recently been 
redescribed as a separate species (Orr 
and Blackburn, 2004). The light and 
dark color variations previously de- 
scribed for S. ciliatus (Tilesius, 1813) 
have been defined as two distinct spe- 
cies: S. ciliatus and S. variabilis. Se- 
bastes ciliatus is the shallow water, 
dark variant that is now commonly 
called “dark rockfish,” and S. varia- 
bilis is the deepwater, light variant 
which is now called “dusky rockfish.” 
Dark rockfish are caught on shallow, 
nearshore rocky reefs and dusky rock- 
fish are found less frequently in near- 
shore habitats and are often captured 
in large aggregations over the outer 
continental shelf (Orr and Blackburn, 
2004). Dusky rockfish are patchily 
distributed; concentrated groups are 
found near the mouths of submarine 
gullies or canyons and along sub- 
merged banks (Reuter, 1999). 
Before this study, estimates of 
dusky rockfish maturity for the Gulf 
of Alaska were based on visual ob- 
servations of gonad maturity from 
a limited sample of this species in 
the Kodiak Island area. Previous 
work revealed the potential for in- 
correct identification of oocyte de- 
velopmental stages with the macro- 
scopic method in comparison to 
studies where the histological eval- 
uation method has been used (Mc- 
Dermott, 1994; Zimmerman, 1997). 
Dusky rockfish growth parameters 
were derived from data sets collected 
before the redescription of dark and 
dusky rockfish. 
The objective of this study was to 
provide improved life history data for 
the newly described dusky rockfish by 
1) producing histologically derived es- 
timates of the age and length at 50% 
maturity (A 0 5 and L 0 5 ); 2) describing 
the seasonal timing of ovary develop- 
ment in female dusky rockfish; and 3) 
comparing growth rates and weight- 
length relationships derived from the 
maturity-estimate samples to a larger 
data set collected in the central Gulf 
of Alaska for both male and female 
dusky rockfish. 
In the Gulf of Alaska, manage- 
ment of the dusky rockfish resource 
is aided by the annual pelagic shelf 
rockfish stock assessment and fisher- 
ies evaluation process, with the use 
of a fishery-independent age-based 
