90 
Fishery Bulletin 1 14(1) 
ued at more than $100 million annually (Fissel et al. 1 ). 
In Alaska, the sablefish population is assessed annu- 
ally with a split-sex, age-structured population model 
(Hanselman et al. 2 ). Age at maturity is an integral 
component for estimating female SSB, which is used 
to set target biological reference points for this stock. 
The current female age-at-maturity model is based on 
data collected during surveys conducted in the sum- 
mers of 1978-1983 (Sasaki, 1985). Because these data 
were collected more than 30 years ago, it is important 
to re-assess the age at maturity of female sablefish. 
In addition to potentially being outdated, those age- 
at-maturity data are from summer samples for which 
maturity was evaluated macroscopically and was not 
confirmed with histological examination. These ma- 
turity data were also categorized by fish length, the 
values of which were later converted to ages for stock 
assessments, introducing further error through the use 
of an age-length key. 
The sablefish is a batch spawner with group syn- 
chronous oocyte development and determinate fecun- 
dity. This species spawns during the winter or early 
spring in Alaska. Before this period, immature fish 
can be unambiguously distinguished from fish that 
will spawn, and total fecundity can be calculated. Dur- 
ing the summer, gonads may be resting and may not 
show obvious signs that sablefish will spawn in the 
coming winter; therefore, fish that will skip spawning 
are difficult to distinguish from fish that will spawn 
if they are sampled during the summer. If maturity is 
consistently misclassified when summer samples are 
used, then estimates of maturity at age can be biased. 
Skipped spawning has not been documented in sable- 
fish, but skipped spawning rates that have been ob- 
served in other species have ranged from 9% to 86% 
(Secor, 2008). 
Since 1996, maturity classifications and age data 
have been collected during the annual summer long- 
line surveys conducted by the NOAA Alaska Fisher- 
ies Science Center (AFSC) in Alaska to sample the 
slope of the Gulf of Alaska, the eastern Bering Sea, 
and the Aleutian Islands from the end of May through 
the end of August. Approximately 1000 females are as- 
sessed for maturity each year, and about 600 of them 
are aged. These data have not been incorporated into 
estimates of age at maturity for stock assessment, but 
they continue to be collected annually. Until our work 
1 Fissel, B. M. Dalton, R. Felthoven, B. Garber- Yonts, A. Haynie, 
A. Himes-Cornell, S. Kasperski, J. Lee, D. Lew, L. Pfeiffer, J. 
Sepez, and C. Seung. 2012. Stock assessment and fishery 
evaluation report for the groundfish fisheries of the Gulf of 
Alaska and Bering Sea/Aleutian Islands area: economic sta- 
tus of the groundfish fisheries off Alaska, 2011, 299. Alaska 
Fish. Sci. Cent., Natl. Mar. Fish. Serv., NOAA, Seattle, WA. 
[Available at website, accessed July 2014.] 
2 Hanselman D. H., C. R. Lunsford, and C. J. Rodgveller. 2013. 
Assessment of the sablefish stock in Alaska. In Stock as- 
sessment and fishery evaluation report for the groundfish 
resources of the Gulf of Alaska, p. 267-376. North Pacific 
Fishery Management Council, Anchorage, AK. [Available at 
website, accessed July 2014.] 
occurred, there had been no studies of sablefish ma- 
turity in winter to compare with the estimates of age 
at maturity in summer, and there are no estimates of 
fecundity for sablefish in Alaska. 
There were multiple objectives for this study. The 
first objective was to estimate the age at maturity for 
prespawning female sablefish caught near the epicen- 
ter of their distribution in Alaska and to determine 
whether females reproduce annually. The second objec- 
tive was to compare estimates of age at maturity based 
on histological data from samples collected in winter 
with estimates of age at maturity based on macroscopic 
examination of samples collected in summer. The third 
objective was to determine whether SSB is proportion- 
al to fecundity, as is assumed in the population models 
for sablefish. 
Materials and methods 
Winter sampling 
The study area was located off Kodiak Island in the 
Gulf of Alaska between latitudes 59°03' and 56°30'N 
and longitudes 148°26' and 154°35'E. A commercial 
trawl vessel, the FV Gold Rush, was chartered to con- 
duct 10 days of fishing beginning 12 December 2011, a 
period that was estimated to be within the prespawn- 
ing period for sablefish. To locate specimens for the full 
range of ages and lengths of mature and immature fe- 
males, trawling operations were planned for sampling 
over a wide range of depths and topography, including 
the continental slope (depths of 500-700 m) and the 
shelf (depths shallower than 300 m), which included 
bays, gullies, and troughs. Locations were chosen on the 
basis of catches from commercial fisheries and AFSC 
bottom trawl surveys. Because of inclement weather, 
only 4 tows were conducted on the slope, whereas 37 
tows were completed on the shelf. 
Maturity samples were collected on the basis of 
a length-stratified sampling design in which up to 7 
sablefish were sampled for each centimeter of total 
length. Each specimen was weighed with the stomach 
evacuated, and the sagittal otoliths were collected for 
aging. Both ovaries were excised and weighed. Ova- 
ries were preserved in 10% formalin. Personnel of the 
AFSC Age and Growth Program aged otoliths by using 
standard validated methods (Fargo and Chilton, 1987; 
Kimura and Anderl, 2005; Kimura et al., 2007). 
Maturity classification during winter 
We prepared histological samples from the posterior re- 
gion of the ovaries for all fish sampled. In addition, for 
a subsample of specimens representing a range of ova- 
ry sizes, the consistency of oocyte development within 
the ovaries was assessed by using sections from the 
medial and anterior areas of one ovary and from the 
posterior section of both ovaries. In another subsample 
of fish, posterior sections were taken from both ovaries. 
