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Fishery Bulletin 1 14(1) 
indicate that skipped spawning rates may be related 
to annual environmental conditions and that skipped 
spawning should be monitored in the future before any 
conclusions are made on rates in the Alaska population 
of sablefish. Measurements of relative liver size during 
the summer may be a good indicator of whether a sa- 
blefish will spawn in the coming winter; relative liver 
size could prove to be a good alternative to histological 
analysis during the summer. We intend to explore the 
relationship between energy reserves, spawning, and 
egg production in the future by sampling both during 
summer longline surveys and during the winter pre- 
spawning period. 
Maturity status determined during the summer may 
be reasonably close to that determined from observa- 
tions made in the winter, but maturity values based on 
summer longline surveys are not as accurate. The vari- 
ability we observed in the estimates from annual sum- 
mer longline surveys may be attributed to sample size, 
subjectivity of maturity classification, or fluctuations in 
the age at maturity or skipped spawning. Inaccuracy 
in estimates from summer longline surveys could also 
be the result of survey timing; some fish macroscopi- 
cally classified as immature during summer surveys 
may become visibly mature later in the fall and win- 
ter, closer to spawning. Another factor that may have 
caused inaccuracy in estimates is that examination for 
skipped spawning was not part of the sampling proto- 
col on summer sampling cruises. 
It is unknown when fish that would skip spawning 
stop progressing in development and become distin- 
guishable from spawning fish. For example, in Atlan- 
tic cod, fish that would skip spawning could be distin- 
guished histologically at approximately 3 months be- 
fore spawning but not before (Skjaeraasen et al., 2009). 
If sablefish have a similar development time, this pe- 
riod for distinguishing fish that would skip spawning 
would fall around October or November, a time that 
is several months after the end of the annual sum- 
mer longline surveys. In the future, it will be impor- 
tant to determine the months when immature, skipped 
spawning, and prespawning sablefish can be differenti- 
ated from one another — in order to accurately classify 
maturity during portions of summer longline surveys, 
which extend from May through August. Because they 
exhibited the resting type of skipped spawning and 
never developed maturing oocytes, fish that will skip 
spawning can be identified by the absence of vitellogen- 
ic oocytes and a thick ovarian wall. Sablefish that will 
spawn may also have greater energy reserves before 
spawning; therefore, measurements of body condition 
and relative liver weight may be useful for predicting 
spawning (as seen in Atlantic cod, Skjaeraasen et al., 
2009; Skjaeraasen et al., 2012). 
The GSI of fish that would skip spawning and im- 
mature fish were significantly different for sablefish in 
this study. The observation of such a difference may 
not be useful in other species; for example, GSI could 
not be used to separate skipped spawning and imma- 
ture Atlantic cod (Skjaeraasen et al., 2012). However, 
this measurement holds great promise for separating 
immature from skipped spawning sablefish. Although 
both of these maturity categories showed only early 
developing, immature oocytes, the additional tissue, 
such as stroma, blood vessels, and ovarian wall, that 
we found in the ovaries of fish that would skip spawn- 
ing, is likely to contribute to the difference observed in 
GSI values. More data is needed on the GSI of fish that 
skip spawning to improve our confidence in the use of 
GSI as a tool for determining maturity. 
Comparing the maturity data from the annual sum- 
mer longline surveys conducted in the Gulf of Alaska, 
the Aleutian Islands, and the eastern Bering Sea would 
be beneficial because each fixed station is sampled on 
the same date each year. Differences in estimates of 
age at maturity for sablefish from these areas may be 
a function of the phase of the reproductive cycle when 
fish were collected. For example, the Bering Sea is sam- 
pled in early June, whereas the western Gulf of Alaska 
is sampled in late August. Ovaries sampled in late Au- 
gust will be more developed and are likely to result in 
different estimates of age at maturity. Because of the 
bias that may be introduced as a result of sampling 
date, winter sampling in multiple areas also is needed 
to determine whether there is truly geographic vari- 
ability in maturity at age and skipped spawning. Dif- 
ferences in the age and length at maturity have been 
documented in sablefish off the coast of the United 
States, south of Canada (Head et al., 2014); therefore, 
it will be important to consider geographic differences 
farther north in Alaska as well. 
Our estimates of fecundity were similar to those for 
sablefish off California (Hunter et al., 1989), but they 
were higher than estimates from a study off of British 
Columbia, Canada (Mason et al., 1983). We compared 
the fecundity of females that were 700 mm in total 
length in our study with fecundity determined from 
other studies because this length is approximately the 
average female size in the longline fishery for sablefish 
in Alaska (Hanselman et al. 2 ). The average fecundity 
for females 700 mm in total length was 412,000 eggs — 
a level that was very similar to an estimate from Cali- 
fornia of 416,000 eggs (Hunter et al., 1989) but more 
than double the estimate of 182,000 eggs from the Brit- 
ish Columbia study (Mason et al., 1983). A microscopic 
examination of ovarian tissue samples for evidence 
of postovulatory follicles was not undertaken in the 
Canadian study; therefore, batch spawning may have 
occurred but was undetected. If batch spawning oc- 
curred, it would decrease the estimated total fecundity 
and would explain why other studies found higher es- 
timates. Batch spawning was documented for sablefish 
off central California (Hunter et al., 1989) and likely 
also occurs in other geographic areas. 
We found no significant relationship between rela- 
tive fecundity and age. This verifies the assumption 
made in the Alaska sablefish population model that 
relative reproductive output is linearly related to fe- 
male spawning biomass and does not change with age. 
There were few fish older than 25 years (3 fish out of 
