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Fishery Bulletin 117(3) 
immature fish that have not previously reproduced ini¬ 
tiate oocyte development through vitellogenesis but have 
this process interrupted and their developing oocytes 
reabsorbed (Hannah and Parker, 2007; Conrath and 
Knoth, 2013). This phenomenon is commonly found in 
species that are members of the genus Sebastes (Nichol 
and Pikitch, 1994). It can be distinguished histologically 
because immature individuals will have no evidence of a 
prior spawning (beta and delta atresia or postovulatory 
follicles). In contrast to work that has examined abortive 
maturity that occurs in immature individuals, analysis 
of reproductive failure in this study included only those 
individuals that had reproduced in a prior year and were 
classified as mature adults. Almost all the individuals 
captured for this study were adults, and the average 
size of fish captured for this study (light dusky rockfish: 
458 mm FL; northern rockfish: 414 mm FL) was quite a bit 
larger than the previously reported size at 50% maturity 
of either species, 310 mm FL for northern rockfish and 
365 mm FL for light dusky rockfish (Chilton, 2007, 2010). 
This difference in size and maturity is likely the reason 
that no individuals undergoing abortive maturation were 
collected during this study. 
Skipped spawning may ensure that fish of these species 
spawn only in years when adequate energy is available to 
produce viable embryos or to optimize their lifetime repro¬ 
ductive output. This pattern may be particularly import¬ 
ant for rockfish species in Alaska that are long lived and 
have a periodic life history strategy (Winemiller and Rose, 
1992). Skipped spawning may occur when fish experience 
decreased food availability (Rideout and Rose, 2006; McBride 
et al., 2015) and may be related to condition and energy 
reserves (Skjaeraasen et al., 2012; Skjaeraasen et al., 2015). If 
skipped spawning is related to energy reserves, it will likely 
vary temporally and the proportion of skipped spawners will 
fluctuate with changing environmental conditions. Interan¬ 
nual variability in the amount of skipped spawning has been 
documented for several teleost species, including haddock 
(Melanogrammus aeglefinus) in the northeast Arctic Ocean 
(Skjaeraasen et al., 2015), Atlantic cod ( Gadus morhua) off 
Newfoundland and Labrador, Canada (Rideout et al., 2006), 
and spring-spawning Atlantic herring ( Clupea harengus ) 
off Norway (Engelhard and Heino, 2006). It is important to 
consider not only annual changes in the amount of skipped 
spawning but spatial differences in rates of skipped spawn¬ 
ing across the geographic range of a species. 
The lack of fertilization type of skipped spawning has not 
been documented in rockfish species in this region prior to 
this study. This type of skipped spawning is similar to the 
retained type of skipped spawning described in Rideout et al. 
(2005) but differs for the live bearing species of the genus 
Sebastes because it is caused by lack of fertilization. In north¬ 
ern rockfish, there is some evidence from this study that the 
fertilization failure type of skipped spawning occurred more 
frequently in smaller fish (<42 cm FL); this relationship 
was not apparent in light dusky rockfish. Additional studies 
examining how incomplete fertilization or fertilization failure 
may relate to sex ratios, mate availability, mating behavior 
and competition, and female size and experience are needed. 
However, it is suspected that the lack of fertilization suc¬ 
cess observed in this study may be due to a large copepod 
parasite ( Sarcotaces sp.) that can be found within the body 
cavity of rockfish species. This parasite is found encysted 
in the skin and muscle tissue of marine fish, particularly in 
members of the genus Sebastes in the North Pacific Ocean 
(Meyers et al. 1 ). In some species, this parasite may form a 
physical blockage in the body cavity or the reproductive 
tract and create problems with fertilization and spawning 
events. This parasite appears to occur frequently in dusky 
rockfish (Sebastes ciliatus ) (Worton 2 ), and this parasite 
is frequently seen in both light dusky and northern rock¬ 
fish. The presence and number of this parasite were not 
consistently recorded in this study; therefore, calculating 
a correlation value between this parasitism and lack of 
fertilization was not possible. Further study is needed to 
examine the correlation between reproductive failure and 
the presence of this parasite. 
Reproductive failure of northern and light dusky 
rockfish has not been documented in prior studies that 
examined the reproductive parameters of these species 
in the Gulf of Alaska (Chilton, 2007, 2010). TenBrink and 
Spencer (2013) in a study of the reproductive biology of 
Pacific ocean perch and northern rockfish mentioned that 
a small number of specimens may have been skipped 
spawners on the basis of the presence of postovulatory 
follicles and atretic oocytes, but skipped spawning appar¬ 
ently was not common. Specimens for this project were 
collected in 2014, when there was a warmwater anomaly 
in the Gulf of Alaska. This mass of warm water devel¬ 
oped in the northeast Pacific Ocean during the winter 
of 2013-2014, and anomalies of warm sea-surface tem¬ 
peratures reached coastal waters of Alaska in May 2014 
(Bond et al., 2015). This area of warm water was present 
through the end of 2015 and had widespread impacts 
on the oceanic and coastal ecosystems of the northeast 
Pacific Ocean (Cavole et al., 2016). It is possible that the 
2 reproductive years covered by my study were impacted 
by this warmwater mass or other environmental condi¬ 
tions specific to this time period, and additional study of 
these processes during a more comprehensive time span 
is needed. 
The greater contribution larger females make to several 
aspects of reproductive potential has been documented 
for members of the genus Sebastes; these aspects include 
increased fecundity (Beyer et al., 2015), increased lar¬ 
val quality (Berkeley et al., 2004), and earlier spawning, 
more protracted spawning, or both (Sogard et al., 2008). 
The results of this study indicate that larger females have 
higher relative fecundity and are less likely to experi¬ 
ence total reproductive failure. The pattern of decreasing 
reproductive failure appears to be driven by a decrease in 
1 Meyers, T., T. Burton, C. Bentz, J. Ferguson, D. Stewart, and 
N. Starkey. 2019. Diseases of wild and cultured fishes in Alaska, 
128 p. Alaska Dep. Fish Game, Anchorage, AK. [Available from 
website.] 
2 Worton, C. 2018. Personal commun. Alaska Department of Fish 
and Game, 351 Research Ct., Kodiak, AK 99615. 
