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Fishery Bulletin 112(4) 
The life history of the North Pacific giant octopus 
has been examined in other parts of their range, par- 
ticularly in Japanese waters (Kanamaru, 1964; Kana- 
maru and Yamashita, 1967; Sano et ah, 2011) and in 
Canadian waters near British Columbia (Gabe, 1975; 
Robinson, 1983). However, there is a lack of informa- 
tion on the biology and ecology of all octopus species 
in the Gulf of Alaska. These data are needed to de- 
termine bycatch limits and management strategies for 
octopus species within this region. The objective of this 
study was to examine the reproductive biology of the 
North Pacific giant octopus within the Gulf of Alaska, 
specifically to determine the seasonality of reproduc- 
tion, size at maturity, and fecundity of this species in 
this region. 
Materials and methods 
Maturity stages 
Specimens of the North Pacific giant octopus were 
obtained from the Gulf of Alaska from commercial 
fishermen during February 2010, the Alaska Fisher- 
ies Science Center bottom-trawl survey of the Gulf 
of Alaska in the summer of 2011, and charter opera- 
tions near Kodiak Island during the period from May 
2010 to December 2011. Octopuses were identified as 
North Pacific giant octopus on the basis of characteris- 
tics presented in Jorgensen (2009). Charter operations 
occurred within Chiniak Bay and specimens from the 
bottom-trawl survey were collected at 4 locations in 
the western and central Gulf of Alaska (Fig. 1). The 
exact location of specimens donated from commercial 
fishermen is unknown, but specimens were captured in 
the Gulf of Alaska near Kodiak Island. A total of 154 
specimens were collected. These specimens, including 
both females (n=71) and males (n=83), ranged in size 
from 1.2 to 25.2 kg. 
All sampled octopuses were weighed, their sex was 
determined, and their reproductive tracts were removed 
and weighed. The weight and diameter of each gonad 
was measured, and the condition of the reproductive 
tract was noted. Female reproductive structures were 
examined for the presence of spermatophores or other 
evidence of mating activity. A 3-stage maturity clas- 
sification system was developed as part of this study 
for both male and female North Pacific giant octopuses 
on the basis of characteristics of the reproductive tract 
and the presence or absence of well-developed eggs or 
spermatophores. 
On the basis of this classification system, which is 
a modification of the classification system presented in 
a report by the Fisheries and Oceans Canada, 1 each 
specimen was assigned a maturity stage of 1 (imma- 
1 Fisheries and Oceans Canada. 2003. Pacific regions: 2003 
experimental harvest guidelines, octopus by dive, January 
16, 2003 to July 31, 2003, 21 p. [Available from http://www. 
dfo-mpo.gc.ca/Library/3 15447.pdf.] 
ture), 2 (maturing), or 3 (mature). A female was con- 
sidered immature (stage 1) if it possessed an ovary 
that was small (diameter <65 mm) and white and had 
eggs not easily visible; maturing (stage 2) if its ovary 
was larger (diameter 69-90 mm) and had small, white, 
or pale-yellow eggs; and mature (stage 3) if its ovary 
was large (>100 mm) and yellow and the majority of 
eggs were large (>5 mm), dark, and yellow. A male was 
considered immature (stage 1) if its reproductive tract 
was transparent and undifferentiated, maturing (stage 
2) if its reproductive tract contained well-developed 
accessory structures but had no fully developed sper- 
matophores, and mature (stage 3) if visible and fully 
developed spermatophores were present within its re- 
productive tract. 
For all specimens, all or part of the gonad was pre- 
served. Thin sections of these tissues were embedded 
in paraffin and stained through the use of standard 
histological techniques (Sheehan and Hrapchak, 1980). 
These sections were used to verify the visual assess- 
ment of the gonad and to measure egg size in female 
octopuses. 
Size at maturity 
Octopus size at maturity was assessed because ag- 
ing of cephalopods is difficult (Guerra et al., 2010) 
and there is no established procedure for aging of the 
North Pacific giant octopus. Octopus lengths are dif- 
ficult to measure consistently because of the fluidity of 
octopus movement and differences found in measure- 
ment of live (mantle contracting) and dead (mantle 
not contracting) octopuses. The weight at maturity 
of octopuses is generally assessed in studies of octo- 
pus biology (Hernandez-Garcla et ah, 2002). A gonad- 
osomatic index (GSI) was calculated for each octopus 
sampled by dividing the wet weight of the reproduc- 
tive tract by the total wet weight of the octopus. A 
variety of GSI-type indices have been used in octopus 
reproductive studies (Perez and Haimovici, 1991; Cor- 
tez et al., 1995; Quetglas et ah, 2005). For this study, 
the simplest method was chosen. Gonadosomatic in- 
dex values for both males and females were examined 
across all size ranges to see if there was a pattern in 
development. 
Weight at 50% maturity (W50) was estimated by fit- 
ting the data to the following logistic equation: 
Y = l/(l + e-(a + MO), 
where Y = the proportion of specimens that were ma- 
ture at weight X\ 
a and b = parameters of the model; and 
X = the weight of the octopus. 
This model was chosen because of its wide application 
in fisheries research and because logistic models are 
prevalent in recent octopus research (Quetglas et al., 
2009; Sifner and Vrgod, 2009). Parameters were fit- 
ted to the logistic equation with a generalized linear 
