REVIEW OF THE SYSTEMATICS AND ECOLOGY OF OOEANIC SQUIDS
139
sexually mature a t 20.0-25.0 cm (mantle length). In the male the
hectocotylus appears at 17.6-19.0 cm (mantle length) (Sasaki, 1921).
The largest female known to the author has a mantle length of
49.3 cm (Katoh, 1959).
The sex ratio a t different sizes and seasons varies considerably
(Katoh, 1959). Tauti (1941) calculated the survival rate as 0.67.
The main foods are Maurolicus muelleri japonicw in coastal regions
and Parathemisto (Parathemisto) japonica in offshore regions (Okiyama,
1965). Larval and young stages of Todarodes pacijcus are an important
part of the diet (Okutani, 1962; Okiyama, 1965). A t Ito, Okutani
(1962) found that 37% of squids (291) had empty stomachs and 80%
of them with food contained less than 1% of the body weight. He
found no seasonal differences. One squid contained food weighing
over one-sixth of the body weight. Fifty per cent of those with food
contained fish, 9% contained crustacea and 7% contained molluscs
(as the principal food?). The fish were myctophids and Engraulis
japonica (anchovies). Crustacea included megalopa larvae of brachyuran
decapods, amphipods, copepods including Calanus darwini and
Euchirella sp. and Cypris larvae. Other food items included Xagitta sp.,
Tomopteris pacijca and a gastropod larva (Tonna). The peak period
in feeding occurs at about sunset when the deep scattering layer
arrives at the surface (Okiyama, 1965).
Predators of the species include Raja (Sasaki, 1920), Coryphaena
hippurus (Kojima, 1961), Balaen whales (Nemoto, 1957) and the
Northern fur seal (Wilke and Kenyon, 1954).
The great economic importance of this species has been touched on
above.
I . Nototodarus
The species of this Pacific Ocean genus have been confused with one
another and with Todarodes pacificus in the literature. Nototodarus is
distinguished by having males with both ventral arms hectocotylized.
Voss (1963a) considers that the four forms within the genus are really
FIG. 18. Tentative growth curves of Todarodes aagittaluefrom Icelandic and Norwegian
waters (upper graph) and T . paci$cus. T . sagittatus is derived from sample means
published by Fridriksson (1943) with the exception of the point for March which
represents the mode of a large sample (over 600) caught in commercial trawls and
measured by the author. T. paci$cus is derived from Katoh (1969). The means
are based on very large commercial catches and the apparent drop from the
possible growth curve in November and December is probably cauaed by mortalities
after spawning. Very tentative parts of the curves are shown with broken lines.
In T. aagitbtw, the period of spawning (broken arrows) is only known from very
few specimens. In T. pacijicua spawning is thought to take place mainly in the
Autumn (hatched).
139
sexually mature a t 20.0-25.0 cm (mantle length). In the male the
hectocotylus appears at 17.6-19.0 cm (mantle length) (Sasaki, 1921).
The largest female known to the author has a mantle length of
49.3 cm (Katoh, 1959).
The sex ratio a t different sizes and seasons varies considerably
(Katoh, 1959). Tauti (1941) calculated the survival rate as 0.67.
The main foods are Maurolicus muelleri japonicw in coastal regions
and Parathemisto (Parathemisto) japonica in offshore regions (Okiyama,
1965). Larval and young stages of Todarodes pacijcus are an important
part of the diet (Okutani, 1962; Okiyama, 1965). A t Ito, Okutani
(1962) found that 37% of squids (291) had empty stomachs and 80%
of them with food contained less than 1% of the body weight. He
found no seasonal differences. One squid contained food weighing
over one-sixth of the body weight. Fifty per cent of those with food
contained fish, 9% contained crustacea and 7% contained molluscs
(as the principal food?). The fish were myctophids and Engraulis
japonica (anchovies). Crustacea included megalopa larvae of brachyuran
decapods, amphipods, copepods including Calanus darwini and
Euchirella sp. and Cypris larvae. Other food items included Xagitta sp.,
Tomopteris pacijca and a gastropod larva (Tonna). The peak period
in feeding occurs at about sunset when the deep scattering layer
arrives at the surface (Okiyama, 1965).
Predators of the species include Raja (Sasaki, 1920), Coryphaena
hippurus (Kojima, 1961), Balaen whales (Nemoto, 1957) and the
Northern fur seal (Wilke and Kenyon, 1954).
The great economic importance of this species has been touched on
above.
I . Nototodarus
The species of this Pacific Ocean genus have been confused with one
another and with Todarodes pacificus in the literature. Nototodarus is
distinguished by having males with both ventral arms hectocotylized.
Voss (1963a) considers that the four forms within the genus are really
FIG. 18. Tentative growth curves of Todarodes aagittaluefrom Icelandic and Norwegian
waters (upper graph) and T . paci$cus. T . sagittatus is derived from sample means
published by Fridriksson (1943) with the exception of the point for March which
represents the mode of a large sample (over 600) caught in commercial trawls and
measured by the author. T. paci$cus is derived from Katoh (1969). The means
are based on very large commercial catches and the apparent drop from the
possible growth curve in November and December is probably cauaed by mortalities
after spawning. Very tentative parts of the curves are shown with broken lines.
In T. aagitbtw, the period of spawning (broken arrows) is only known from very
few specimens. In T. pacijicua spawning is thought to take place mainly in the
Autumn (hatched).