Conrath: Reproductive potential of Sebastes variabilis and 5. polyspinis 
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Fork length (mm) 
Figure 5 
Proportion of northern rockfish (Sebastes polyspinis) and light dusky 
rockfish (S. variabilis), captured in May 2014 in the Gulf of Alaska, 
that experienced skipped spawning caused by fertilization failure 
(open circles or diamonds) or the resting type of skipped spawning 
(black circles or diamonds), by fork length. 
P=0.278; northern rockfish: P=0.096). The quasi-binomial 
models all had dispersion values that were close to 1 (< 1.1), 
indicating that there was little overdispersion in all of 
these models. 
Discussion 
Light dusky and northern rockfish within the Gulf of Alaska 
have a highly synchronous reproductive cycle with nearly all 
individuals having ovaries dominated by oocytes or embryos 
in the same state of development in any period of the year. 
I calculated similar GSI values for both species during each 
of the 2 seasons. Although I sampled only during 2 peri¬ 
ods of the year, results from this study are consistent with 
a synchronous annual cycle with parturition occurring in 
the early summer months. Fish of both species captured 
in December were in mid-vitellogenesis, and those captured 
in May were in late embryogenesis, indicating that they were 
nearing parturition. This timing is similar to that reported 
for northern rockfish in the Gulf of Alaska by Chilton (2007), 
who observed parturition occurring from April through June. 
Similarly, May has previously been reported as the peak 
month of parturition for light dusky rockfish in the Gulf of 
Alaska (Chilton, 2010). Northern rockfish in the Aleutian 
Islands appear to have a similar reproductive cycle, but the 
peak month of parturition is April (TenBrink and Spencer, 
2013), indicating that reproductive events may occur earlier 
in the year in the region of the Aleutian Islands. 
Fecundity estimates for both species were lower during 
the spring. Some loss of embryos occurred during capture 
in May because embryos are expelled as a result of the 
expansion of the swim bladder, potentially contributing 
to lower fecundity estimates during this period. However, 
it is also possible that some decrease in fecundity occurs 
during oocyte development. It is important to note that 
collections for this study occurred during 2 different repro¬ 
ductive cycles with the collections in May occurring in the 
reproductive year of 2014 and the collections in December 
occurring in the following reproductive year of 2015, and 
there may be interannual differences in fecundity due to 
environmental factors. It is assumed that the fecundity 
estimates for specimens collected in December may be more 
accurate because of the difficulty of collecting whole ovaries 
in May during the period of time close to parturition. 
There are no published estimates of fecundity for either 
of these species in the Gulf of Alaska, but fecundity of north¬ 
ern rockfish has been examined in the Aleutian Islands. 
TenBrink and Spencer (2013) found that average fecun¬ 
dity of this species was 89,320 oocytes for northern rock¬ 
fish ranging in size from 28 to 43 cm FL. They found that 
individuals of this species produce more oocytes than is 
explained by a proportional relationship between fecun¬ 
dity and maternal weight. The large disparity between 
the mean fecundity reported by TenBrink and Spencer 
(2013) and the mean fecundity calculated in this study is 
likely due to the larger sizes of fish examined in our study 
(37-46 cm FL). For most Sebastes species, there is a rela¬ 
tionship between fecundity and size of fish, and for many 
of these species relative fecundity increases with the size 
of fish (Boehlert at al., 1982; Bobko and Berkeley, 2004; 
Dick, 2009). 
It is important to distinguish reproductive failure from 
abortive maturation. Abortive maturation occurs when 
