98 
Fishery Bulletin 1 14(1) 
Table 2 
Slope and age at 50% maturity ( 050 %) determined from logistic models of age at ma- 
turity for female sablefish (Anoplopoma fimbria) sampled before spawning during 
winter (in December 2011) in the central Gulf of Alaska, during summer (May-Au- 
gust), 1996-2012, in the central Gulf of Alaska, and during the summer, 1978-1983, 
in the Gulf of Alaska. For the winter surveys, fish that would skip spawning were 
classified as either mature (m) or immature (i). Fish that would skip spawning were 
not looked for in the summer. 
Survey 
Year 
Slope 
<250 
Winter (m) 
2011 
1.14 
6.77 
Winter (i) 
2011 
0.56 
9.88 
Summer 
2011 
0.76 
7.97 
Current assessment 
1978-1983 
0.84 
6.60 
Mean (summer longline survey) 
1996-2012 
0.70 
6.98 
Range (summer longline survey range) 
1996-2012 
0.60-1.30 
5. 5-8.6 
classified as mature. Additionally, the 050 % parameters 
of these logistic models (ranging from 6.60 to 6.98 
years) were very similar to recent estimates of age at 
maturity from the U.S. West Coast that were based on 
histological findings ( 6.86 years) (Head et al., 2014). It 
is unknown if any fish that would skip spawning were 
sampled in those studies. In our study, the small differ- 
ences in the maturity curves at young ages caused dif- 
ferences in estimates of female SSB when there were 
larger than average recruitment classes (see Hansel- 
man et al. 2 for a time series of recruitment). A lower 
SSB translated to lower fishing rates (F^%). Compared 
with data that are currently used in the assessment, 
the data from the surveys conducted in winter 2011 
provided a slightly lower ^ 40 % when fish that would 
skip spawning were classified as mature (0.18%) and 
an F 40 % that was 1.95% lower when these fish were 
classified as immature. A similar situation has been 
reported for Atlantic cod, where an overestimation of 
egg production, by 8-41%, resulted from not accounting 
for fish that had skipped spawning (Rideout and Rose, 
2006). For both species this reduction in SSB should 
result in a lower allowable biological catch. 
For all maturity curves in this study, we used the 
standard model (i.e., a logistic function with asymptote 
at 100%). The standard model was chosen because it 
illustrates how differences in age at maturity would 
impact sablefish management if current methods were 
used. Although we found that skipped spawning in- 
creases with age, our data do not necessarily negate 
the use of the standard logistic model. The standard 
model still could be applicable because the increase in 
skipped spawning occurred at younger ages (4-15), the 
logistic curves reached 100 % around age 12 (close to 
age 15), and fish commonly reach ages >50. There are 
many potential methods for incorporating the loss in re- 
productive output due to skipped spawning depending 
on how skipped spawning is related to age, the longev- 
ity of the species of interest, and the annual or spatial 
variability in skipped spawn- 
ing (e.g., Secor, 2008; Brooks, 
2013). As more data on the 
consistency of skipped spawn- 
ing in the sablefish population 
in Alaska become available, a 
complete evaluation of alter- 
native methods for incorporat- 
ing skipped spawning into the 
assessment is warranted. 
The most direct comparison 
of estimates of age at maturi- 
ty for summer and winter was 
between the samples collected 
in the winter and summer of 
2011. The data from summer 
2011 provided estimates of the 
proportion of mature fish at 
age that were similar to the 
values based on data from the 
winter survey for fish at young 
ages (<5 years) and that were intermediate between 
the 2 winter curves for fish at ages 5-13 years. Use of 
the maturity curve based on data from summer 2011 , 
therefore, produced estimates of SSB, and ^ 40 % that 
were also intermediate. It is possible that during the 
summer some fish that would skip spawning during 
the upcoming winter were classified as mature and 
some as immature, and that is why the resulting sum- 
mer curve was intermediate. It is also possible that 
fewer fish that would skip spawning were encountered 
during the summer surveys. The winter survey cov- 
ered areas on the shelf that were not covered by the 
summer longline survey in 2011 , and the shelf was the 
area where the majority of these fish were found in the 
winter. More winter sampling is needed for comparison 
of winter data with summer data to determine whether 
the difference we saw in data for 2011 is consistent 
over time. 
It is important to note that we pooled samples 
from the shelf and slope to produce an overall matu- 
rity curve. To test for any bias due to disproportionate 
sampling in relation to the distribution of the popu- 
lation, we weighted our calculations according to the 
abundance of fish in each area; abundance values were 
calculated with data from AFSC bottom trawl surveys 
conducted in summer. There was little difference be- 
tween the values from these calculations and the un- 
weighted results, indicating that our results are reflec- 
tive of the population in Alaska as a whole. 
Movement and habitat use during the spawning 
season have been reported to indicate whether a fish 
is spawning or has skipped spawning for Pacific hali- 
but (Loher and Seitz, 2008) and Atlantic cod (Hussy et 
al., 2009; Jonsdottir et al., 2014). Sablefish are highly 
migratory throughout their lives; in Alaska, 11% of 
tagged fish have been recovered at locations more than 
2000 km from their release sites (Echave et al., 2013). 
However, preliminary data from tagging sablefish dur- 
ing the winter survey in 2011 indicate that sablefish do 
