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Fishery Bulletin 1 14(1) 
cytes. They are considered mature if ovaries are large, 
are turning white but still may have a pinkish hue, 
and veins are developing. For ovaries classified as ma- 
ture, small oocytes are sometimes discernible and are 
firmly attached to the tissue. Fish are spawning if eggs 
are loose or extruding, and they are considered to be 
resting, or spent, if ovaries are flaccid; spent or resting 
ovaries may also have a dark coloration. Interpretation 
of these various stages involves some subjectivity, but 
technicians are trained to standardize their interpreta- 
tion of juvenile and mature ovaries. 
Estimation of age at maturity 
Age at maturity of female sablefish, for both the his- 
tologically analyzed winter samples and the visually 
analyzed summer samples, was modeled with a logistic 
function. The 2-parameter logistic function is given by 
the following equation: 
p a = l/(l + e“' 5(a “ a50%) ), (1) 
where p a = the estimate of the proportion of mature fish 
at age; 
8 = the parameter that describes the slope 
(the speed at which maturity approaches 
100%); and 
° 50 % = the parameter that describes the age at 
which 50% of the fish are mature. 
The observed proportion at age was calculated as 
where m a = the number of mature fish observed at age 
a; and 
n a = the total number of fish at age a. 
We used the binomial likelihood to fit the observed pro- 
portion of mature fish at age with the logistic model 
given in equation 1 in AD Model Builder. 3 vers. 11.2 
(Fournier et al., 2012), with an additional penalty that 
accounted for maturity at age 0 being 0%. 
Age at maturity was estimated for the winter sam- 
ples in 2 ways: 1) fish that would skip spawning were 
classified as mature, and 2) they were classified as im- 
mature. In actuality, fish that would skip spawning are 
not immature but have spawned in the past. In the de- 
termination of maturity during all previous collections 
of sablefish in Alaska, fish that would skip spawning 
were either not distinguished from immature fish or 
could have been considered mature. For comparison 
with these data sets, we ran maturity-at-age models 
with the winter data in which sablefish that would 
skip spawning were classified as either immature or 
mature. 
Age at maturity was analyzed for all samples pooled 
and stratified by area, shelf (depths less than 300 m), 
and slope (depths of 500-700 m), to identify possible 
3 Mention of trade names or commercial companies is for iden- 
tification purposes only and does not imply endorsement by 
the National Marine Fisheries Service, NOAA. 
differences between these habitats. To examine the 
relationship between age and skipped spawning the 
proportion of fish that would skip spawning, by age, 
was examined for the shelf, where fish that would skip 
spawning were much more common; ages for which 
there was only one sample were excluded from this 
analysis. 
Biomass and reference points for target fishing 
Several logistic maturity models were used within the 
age-structured population model currently used for sa- 
blefish in Alaska for determining SSB (Hanselman et 
al. 2 ): these included the logistic model fit to the age-at- 
maturity data from the trawl survey conducted in the 
winter of 2011, the summer longline survey conducted 
in 2011, the mean fit to all data from annual summer 
longline surveys, and the maturity curve currently 
used in stock assessment. 
A time series of female SSB was estimated when 
each maturity curve was input into the sablefish popu- 
lation model. In short, SSB is calculated in the assess- 
ment model with the age structure of the population 
and the age-at-maturity curve (see Hanselman et al. 2 ). 
In addition, F^q%, the fishing rate that reduces SSB 
per recruit (lifetime egg production) to 40% of the un- 
fished level, was estimated, for the most current year 
in the time series, when each of the 4 maturity curves 
was used to determine SSB in the sablefish population 
model. 
Fecundity 
Ovaries were chosen for estimation of fecundity if they 
had advanced vitellogenic oocytes and if no postovula- 
tory follicles were identified in histological cross sec- 
tions; postovulatory follicles would indicate that partial 
spawning had occurred. In ovaries with these features 
an advanced (mature) cohort of oocytes was clearly sep- 
arable from the early developing (immature) cohort on 
the basis of oocyte size and appearance, as described 
for sablefish by Mason et al. (1983) and Hunter et al. 
(1989). This clear separation indicates that sablefish 
have determinate fecundity, in which there is only one 
cohort of maturing oocytes within a spawning season. 
Fecundity was measured with the gravimetric method 
(Murua et al., 2003), whereby a subsample of mature 
oocytes is weighed and the number of oocytes is count- 
ed. The number of eggs per gram in the subsample is 
multiplied by the ovary weight to obtain a total fecun- 
dity. Samples were taken from the anterior, middle, 
and posterior sections of both ovaries, and the 6 mea- 
surements were averaged to estimate overall fecundity. 
As ovaries develop, oocytes enlarge and the number 
of oocytes per gram of sample weight decreases. Such 
a decrease will not affect estimates of fecundity un- 
less the decrease is caused by a loss of oocytes through 
batch spawning or atresia. To confirm that spawning 
had not commenced, a linear regression of oocytes per 
gram of subsample weight and fecundity was computed 
