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Fishery Bulletin 1 12(4) 
Fecundity 
Fecundity was estimated for stage-2 and stage-3 fe- 
males with developing eggs within their ovaries. The 
fecundity of stage-1 females was not examined because 
of a lack of development of some stage-1 females and 
the small size of eggs found within the ovaries of these 
females. For each female classified as stage 2 or 3, a 
sample that weighed between 1.5 and 3 g was removed 
from the ovary and all eggs within it were counted with 
a dissecting microscope. This subsample was used to 
estimate the total number of eggs within an ovary by 
applying a gravimetric approach. With this approach, 
the estimated individual egg weight was used in com- 
bination with the weight of the whole ovary to estimate 
the number of eggs found within each ovary. The rela- 
tionship between total body weight and fecundity for 
females was plotted, and an exponential regression line 
was fitted to the data with R software. 
Results 
Size at maturity 
Female GSI values ranged from <0.001 to 0.083 and 
overlapped between stages (Fig. 2A). Female North Pa- 
cific giant octopuses had MOL values ranging from 0.1 
to 8.1 mm. Stage-1 females had MOLs that were <2 
mm, stage-2 females had MOLs ranging from 2.6 to 
7.8 mm, and stage-3 females had MOLs ranging from 
3.6 to 8.1 mm. MOLs of stage-2 females were predomi- 
nately <5.0 mm with one exception, and most MOLs of 
stage-3 females were >5.0 mm. 
Male North Pacific giant octopuses had GSI values 
that ranged from <0.003 to 0.082 (Fig. 2B). The over- 
lap in GSI values for all stages is a reflection of the 
large size range of stage-2 males. Many stage-2 males 
possessed reproductive structures that were well-de- 
veloped and large but lacked spermatophores. Because 
spermatophores are necessary for successful mating, 
these male octopuses were determined to be stage 2. 
They all appeared to be healthy — without any obvious 
signs of senescence (reduced body condition or uncoor- 
dinated body movements), and we assumed that they 
had been captured before maturation rather than after 
mating. 
Size at maturity was highly variable for both sexes, 
but it was particularly so for male North Pacific giant 
octopuses. The smallest mature male was 7.5 kg, and 
the largest immature male was 22.5 kg (Fig. 2A). The 
smallest mature female was 9.2 kg, and the largest im- 
mature female was 18.0 kg (Fig. 2B). North Pacific gi- 
ant octopuses <10 kg tended to be immature, but male 
and female members of this species in the size range of 
10-20 kg were found at all 3 maturity stages. Weight 
at 50% maturity for males and females fitted the lo- 
gistic model and was found to be near 14 kg for both 
sexes, but it was highly variable between individuals 
0 2 4 6 8 10 12 14 16 18 20 22 24 26 
Total weight (kg) 
Figure 2 
Gonadosomatic index (GSI) by total weight for (A) all 
female specimens and (B) all male specimens of the 
North Pacific giant octopus ( Enteroctopus dofleini) col- 
lected from the central and western Gulf of Alaska in 
2010-2011. Values are shown for 3 maturity stages: im- 
mature (stage 1), maturing (stage 2), and mature (stage 
3). 
(males, W5o=14.2 kg, P<0.001, 95% confidence interval 
[Cl] = 12.6—15.9 kg; females, W 50 =13.7 kg, P<0.001, 95% 
01=12.5-15.5 kg; Fig. 3). 
Seasonality 
Mature males and females were observed within each 
sampling season (Table 1). The seasonal GSI for fe- 
males peaked in the winter season, was at a minimum 
during spring months, and increased steadily through- 
out the summer and fall (Fig. 4A). The seasonal GSI 
values were significantly different between seasons 
(P<0.001); significant differences were found between 
3 seasonal comparisons: spring and fall (P=0.004); 
winter and spring (P=0.001); and winter and summer 
(P=0.011). These results indicate a significant increase 
