132
MALCOLM R. IYIARKE
Ommustrephes sloanei, 0. sloanei pacijcus, or 0. paciJicus. It is closely
allied to T. sagittatus and is better kept in the same genus (Voss, 1963a).
This is the common Japanese squid and its great commercial importance
has resulted in considerable work on its ecology. It is found (Fig. 13)
on both sides of Japan from Kiushu to Hokkaido (Steenstrup, 1880;
Hoyle, 1886a; Sasaki, 1929a and many other authors), from the
western side of the Inland Sea of Japan (Joubin, 1897b; Kojima, 1961),
from Cape Clonard, Korea (Sasaki, 1929a) and it occurs very rarely in
Sperm whale stomachs caught around the Kuril Islands (Beteshava
and Akimushkin, 1955). Further south, Voss (1963a) did not find it off
the Philippines so it apparently has a rather small area of distribution
for such an active and prolific squid.
The species was first thought to migrate from the south west to the
north east in the Japan sea because the fishing season starts later towards
the north, but Sasaki (1921) found no evidence for this and indeed
detected differences in habit and sexual development between northern
and southern populations. He later (192913) detected south-westerly
movement in spring by marking 1 014 specimens. Mackinaka (1969)
marked over 37 000 and got a recovery rate of 1.16%. Those tagged
in summer near bays tended to move into the bay; some marked
elsewhere migrated towards the coast; the majority, however, were
caught near their liberation points. The mean speed of movement was
1.3 miles per day while the maximum speed found was 17 miles per day.
Nishizawa (1954) considered that the fall off in catch rate of marked
squids showed that migration in the Esan region was ‘‘ diffusive ” and he
calculated the diffusion velocity as 1.8 miles per day. Sasaki (1929b)
reported a squid which moved eight miles in two hours. Mackinaka
(1959) found an intimate relationship between migration and the local
currents. Suzuki (1 963) studied hydrographic conditions and concluded
that off Hokkaido the optimum water temperature for migration was
4°-100C. Summer is the main fishing season (Sasaki, 1929b; Nagata,
1957; Katoh, 1959) but large populations are also present in winter,
and in both seasons large-scale strandings sometimes occur; in some
cases these are possibly due to excitement immediately prior to copulation (Hamabe and Shimizu, 1959). The very large numbers taken
may be judged from catch statistics; the Japanese total catch reached
600870 tons in 1952 and the development of the industry can be
seen from catch statistics going back to before 1900 (Fig. 14 from
Suzuki, 1963). As the mean body length lies somewhere about 23.0
om (Katoh, 1959) which corresponds to a weight of roughly 250 g
(calculated from data on Ommastrephes caroli, a near relative) it will
be seen that somewhere in the region of 24 x lo8 squids were taken in
MALCOLM R. IYIARKE
Ommustrephes sloanei, 0. sloanei pacijcus, or 0. paciJicus. It is closely
allied to T. sagittatus and is better kept in the same genus (Voss, 1963a).
This is the common Japanese squid and its great commercial importance
has resulted in considerable work on its ecology. It is found (Fig. 13)
on both sides of Japan from Kiushu to Hokkaido (Steenstrup, 1880;
Hoyle, 1886a; Sasaki, 1929a and many other authors), from the
western side of the Inland Sea of Japan (Joubin, 1897b; Kojima, 1961),
from Cape Clonard, Korea (Sasaki, 1929a) and it occurs very rarely in
Sperm whale stomachs caught around the Kuril Islands (Beteshava
and Akimushkin, 1955). Further south, Voss (1963a) did not find it off
the Philippines so it apparently has a rather small area of distribution
for such an active and prolific squid.
The species was first thought to migrate from the south west to the
north east in the Japan sea because the fishing season starts later towards
the north, but Sasaki (1921) found no evidence for this and indeed
detected differences in habit and sexual development between northern
and southern populations. He later (192913) detected south-westerly
movement in spring by marking 1 014 specimens. Mackinaka (1969)
marked over 37 000 and got a recovery rate of 1.16%. Those tagged
in summer near bays tended to move into the bay; some marked
elsewhere migrated towards the coast; the majority, however, were
caught near their liberation points. The mean speed of movement was
1.3 miles per day while the maximum speed found was 17 miles per day.
Nishizawa (1954) considered that the fall off in catch rate of marked
squids showed that migration in the Esan region was ‘‘ diffusive ” and he
calculated the diffusion velocity as 1.8 miles per day. Sasaki (1929b)
reported a squid which moved eight miles in two hours. Mackinaka
(1959) found an intimate relationship between migration and the local
currents. Suzuki (1 963) studied hydrographic conditions and concluded
that off Hokkaido the optimum water temperature for migration was
4°-100C. Summer is the main fishing season (Sasaki, 1929b; Nagata,
1957; Katoh, 1959) but large populations are also present in winter,
and in both seasons large-scale strandings sometimes occur; in some
cases these are possibly due to excitement immediately prior to copulation (Hamabe and Shimizu, 1959). The very large numbers taken
may be judged from catch statistics; the Japanese total catch reached
600870 tons in 1952 and the development of the industry can be
seen from catch statistics going back to before 1900 (Fig. 14 from
Suzuki, 1963). As the mean body length lies somewhere about 23.0
om (Katoh, 1959) which corresponds to a weight of roughly 250 g
(calculated from data on Ommastrephes caroli, a near relative) it will
be seen that somewhere in the region of 24 x lo8 squids were taken in