Abstract
In total, 57 giant squid, Architeuthis dux, were found between January 2014 and March 2015 in Japanese coastal waters in the Sea of Japan. Occurrences were especially high around Sado Island and in Toyama Bay. All of the squid occurred individually, and 28 were found alive. The occurrences were categorized into three groups based on distance from the shore and the depth at which they were found: (1) washed ashore on a beach or found floating at the surface close to a beach (19 individuals); (2) caught in a fixed net set in coastal waters between 50 and 150 m depths (28 individuals); and (3) caught by bottom trawl or bottom gillnet fisheries several kilometers offshore between 200 and 300 m depths (ten individuals). Two size groups were recognized, one ranging between 80 and 160 cm dorsal mantle length (DML) with a mode at 110 cm and another larger than 160 cm DML. The sex ratio in the smaller group was nearly equal and the larger group was comprised of all females. The Sea of Japan was considered to be a large natural trap for giant squid migrating through southwestern Tsushima Strait.
Highlights
The giant squid is well known as one of the largest marine invertebrates
Systematic description of A. martensii was inadequate for a distinct species; A. japonica had been applied to the giant squid in Japanese waters (Sasaki 1916, 1929; Taki 1965)
The Sea of Japan is a 978,000-km2 marginal sea, located in the western periphery of the North Pacific. It is bordered by the Eurasian continent to the west and the Japanese archipelago to the east, and is connected to the Okhotsk Sea through the narrow Soya Strait to the north, to the North Pacific through Tsugaru Strait in the east, and to the East China Sea through the narrow Tsushima Strait to the south
Summary
The giant squid is well known as one of the largest marine invertebrates. Marine biologists and the general public have been fascinated by this elusive creature due to their depiction in popular sci-fi novels and movies (Ellis 1998). In Japanese waters, two nominal species, A. martensii (Hilgendorf, 1880) and A. japonica Pfeffer, 1912, the latter of which was named based on BNotes on a gigantic cephalopod^ by Mitsukuri and Ikeda (1895), were initially described. In the early 1980s, Roper and Boss (1982) suggested that the 19 nominal species identified at that time comprised only three species, A. dux in the northern Atlantic, A. japonica in the northern Pacific, and A. sanctipauli in the Southern Hemisphere
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