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optimal light conditions for jigging. Jigs are also used successfully in some of the
smaller long-fin (loliginid) squid fisheries (Hastie et al. 2009).
Trawlers use various types of the trawling gear (pelagic, semi-pelagic, and bottom) which are deployed during daytime to exploit the natural behaviour of squids
over the continental shelf as they aggregate near the seabed during daylight. The
trawling gear used is essentially the same as that used for finfish. Trawlers use
acoustic target-finding technology to locate aggregations of squids. However, squids
provide weak acoustic targets because they lack a swim bladder, so the technology
has limited use where squid targets are mixed with fish possessing swim bladders.
Squid targets can be also confused with aggregations of similar sized fish that do not
have a swim bladder, such as the rock cod Patagonotothen ramsayi (Arkhipkin et al.
2015). Long-fin (loliginid) squid are typically caught by demersal trawling. The
trawls are used during hours of daylight when the squid are concentrated near the
seabed. Several trawl gear types are used for squid fishing. These include: conventional otter trawls, which are used to fish on the bottom over rough ground; pelagic
trawls, which can be used to fish just off the seabed; and specially designed squid
trawls, which tend to have small mesh cod ends and higher head ropes than those
normally used to catch fish (Hastie et al. 2009).
Some Important Species of Squids
There are more than 300 known species of squid out there that have been identified.
About 30–40 species have substantial commercial importance. The bulk of the
global squid catch comprises species from two families, the Ommastrephidae and
Loliginidae. The members of the family Ommastrephidae dominate in terms of biomass with five main commercial species.
Todarodes pacificus (Japanese Flying Squid)
Todarodes pacificus is one of the most abundant of the commercially valuable squid
in the world. An oceanic and neritic species occurring within abroad temperature
range from about 5 to 27 °C, usually in surface waters to 100 m depth and, to a
minor extent, down to 500 m depth. During its lifespan of about 1 year a northward
migration occurs first, followed by another one in southward direction, usually in
close correlation with changes of the main surface currents. Large aggregations
occur in small gyres and along oceanic fronts. Three independently breeding subpopulations can be distinguished in Japanese waters. The main group spawns in
winter in the East China Sea, the second in autumn, west of Kyushu, and the third,
minor group in spring/summer in the Sea of Japan as well as off north eastern Japan.
Post-spawning mortality is very high. The males of all three subpopulations mature
before the females and transfer their spermatophores on the still immature females
(in water temperatures of 13–18 °C). Growth rates are directly related with temperature and inversely with size. Main food items are myctophids, anchovies, crustaceans, gastropod larvae, and chaetognaths. Total coach in 2017 was reported to be
152,839 tons (FAO 2019c). T. pacificus is distributed mainly in the northwest Pacific
3 Molluscan Shellfish
optimal light conditions for jigging. Jigs are also used successfully in some of the
smaller long-fin (loliginid) squid fisheries (Hastie et al. 2009).
Trawlers use various types of the trawling gear (pelagic, semi-pelagic, and bottom) which are deployed during daytime to exploit the natural behaviour of squids
over the continental shelf as they aggregate near the seabed during daylight. The
trawling gear used is essentially the same as that used for finfish. Trawlers use
acoustic target-finding technology to locate aggregations of squids. However, squids
provide weak acoustic targets because they lack a swim bladder, so the technology
has limited use where squid targets are mixed with fish possessing swim bladders.
Squid targets can be also confused with aggregations of similar sized fish that do not
have a swim bladder, such as the rock cod Patagonotothen ramsayi (Arkhipkin et al.
2015). Long-fin (loliginid) squid are typically caught by demersal trawling. The
trawls are used during hours of daylight when the squid are concentrated near the
seabed. Several trawl gear types are used for squid fishing. These include: conventional otter trawls, which are used to fish on the bottom over rough ground; pelagic
trawls, which can be used to fish just off the seabed; and specially designed squid
trawls, which tend to have small mesh cod ends and higher head ropes than those
normally used to catch fish (Hastie et al. 2009).
Some Important Species of Squids
There are more than 300 known species of squid out there that have been identified.
About 30–40 species have substantial commercial importance. The bulk of the
global squid catch comprises species from two families, the Ommastrephidae and
Loliginidae. The members of the family Ommastrephidae dominate in terms of biomass with five main commercial species.
Todarodes pacificus (Japanese Flying Squid)
Todarodes pacificus is one of the most abundant of the commercially valuable squid
in the world. An oceanic and neritic species occurring within abroad temperature
range from about 5 to 27 °C, usually in surface waters to 100 m depth and, to a
minor extent, down to 500 m depth. During its lifespan of about 1 year a northward
migration occurs first, followed by another one in southward direction, usually in
close correlation with changes of the main surface currents. Large aggregations
occur in small gyres and along oceanic fronts. Three independently breeding subpopulations can be distinguished in Japanese waters. The main group spawns in
winter in the East China Sea, the second in autumn, west of Kyushu, and the third,
minor group in spring/summer in the Sea of Japan as well as off north eastern Japan.
Post-spawning mortality is very high. The males of all three subpopulations mature
before the females and transfer their spermatophores on the still immature females
(in water temperatures of 13–18 °C). Growth rates are directly related with temperature and inversely with size. Main food items are myctophids, anchovies, crustaceans, gastropod larvae, and chaetognaths. Total coach in 2017 was reported to be
152,839 tons (FAO 2019c). T. pacificus is distributed mainly in the northwest Pacific
3 Molluscan Shellfish