The diamond squid (Thysanoteuthis rhombus): A review of the fishery and recent research in Japan

Abstract: We review the fishery for the diamond squid (Thysanoteuthis rhombus) in Japan and recent Japanese research conducted on this species. T. rhombus occurs worldwide in tropical and subtropical waters, including near southern and central Japan, where it is targeted by a growing fishery. The annual catch in Japan increased from 339t in 1989 to almost 6000t in 2001, and during 1998–2003, averaged close to 4900t. The main fishing grounds are located in the Sea of Japan, Okinawa Prefecture, and Kagoshima Prefecture, and 90% of the total catch is made in the Sea of Japan and Okinawa. In the Sea of Japan, it is caught with free-floating angling gear called “taru-nagashi” and inshore trap nets; the fishery there usually runs from July to February, with highest catches occurring in September–December. The annual catch in the Sea of Japan during 1998–2003 ranged between 1600 and 3700t. In Okinawa, it is fished primarily in the daytime with free-floating angling gear called “hata-nagashi”; the fishery there runs mainly from November to April, with highest catches occurring in February–April. The annual catch in Okinawa increased from 15t in 1989 to 2300t in 2003. The free-floating egg masses of T. rhombus occur widely in surface waters near southern and central Japan, and paralarval distribution patterns suggest that it spawns over a wide area almost year-round. Part of the population is transported by the Tsushima Current into the Sea of Japan, but little is known about this migration. The vertical distribution of T. rhombus varies regionally; in Okinawa, it occurs mainly at 300–650m depth during the day and 0–150m depth at night, while in the Sea of Japan, it occurs mainly at 75–100m depth during the day and 0–50m depth at night. Its life span is thought to be about 1 year, and squid larger than 30cm mantle length grow about 7–10cmmo−1. [Copyright &y& Elsevier]