|Exploration of the Jumbo Squid, Dosidicus gigas, resources in the Southeastern Pacific Ocean with notes on the history of jigging surveys by the Japan Marine Fishery Resources Research Center|
Kuroiwa, M. (1998). Exploration of the Jumbo Squid, Dosidicus gigas, resources in the Southeastern Pacific Ocean with notes on the history of jigging surveys by the Japan Marine Fishery Resources Research Center, in: Okutani, T. Contributed papers to International Symposium on Large Pelagic Squids, July 18-19, 1996, for JAMARC's 25th anniversary of its foundation. pp. 89-105
In: Okutani, T. (1998). Contributed papers to International Symposium on Large Pelagic Squids, July 18-19, 1996, for JAMARC's 25th anniversary of its foundation. Japan Marine Fishery Resources Research Center: Tokyo. 269 pp., more
Dosidicus gigas is the largest species among the family Ommastrephidae. This "jumbo squid" is abundant in the Peru Current and migrating in the subtropical and tropical waters of eastern Pacific along the coasts of American Continent. Japan Marine Fishery Resources Research Center (JAMARC) initiated in 1971 an exploratory fishing along the coast of Baja Califomia although the survey has been suspended until 1984. Intensive exploratory jigging survey was resumed since 1984 from viewpoint of that D. gigas resource is a possible supplement to those of Ommastrephes bartramii, Nototodarus spp. and Illex spp. Japanese commercial jigging of the "jumbo squid" started to operate in the years around 1988 with the catch amounted 640 tons then. The catches increased year by year up to 80,000 tons in 1994. The present paper discusses distribution, fishing season and ground, and some biological aspects of this species based on exploratory fishing surveys during 1986 to 1994 conducted in the south of the equator in and out of EZ (200 nautical mile zone) of Ecuador and Peru. The surveys aimed to explore new fishing grounds by grasping distribution pattern of this squid and by grouping commercially potential stock through concentrated jigging at "good" spots. The catch statistics and CPUE (catch per machine hour) are all based on automatic jigging machines with occasional hand jigging. High CPUE was located in the high-sea southeast off Galapagos Islands to the north of 10°S during June to September, and also in the south of 10°S after October. Within the Economic Zone of Peru, a good fishing ground was located between 3°S to 9°S in November-December. These surveys thus contributed to an exploration of new fishing grounds of D. gigas for Japanese high-sea squid fisheries. Concerning the relation between water temperature and CPUE, CPUE was low at above 23°C in surface water temperature. Good fishing grounds with high CPUE were usually located where a thermocline lies at 10- 50 m deep with water temperature 14° -15°C at 50 m-stratum. Mantle length range of jumbo squid captured within the High seas, Peruvian 200 nautical mile Economic Zone and Ecuadorian 200 nautical rnile Economic Zone adjacent waters was 11- 62 cm, 15- 76 cm and 12- 98 cm each. Smaller squid less than 35 cm ML was observed for both sexes obtained trom 1984 -1994. Largesized squid over than 60 cm ML class were captured within the Peruvian 200 nautical mile Economic Zone and over than 80 cm ML class, within the Ecuadorian 200 nautical mile Economic Zone. Sex ratio of catches from the high-sea fishing ground, females outnumbered and their size was 1 -3 cm larger than males. Females occupied 76.5- 97.0 % of total squid measured, the mean value from June to March was 87.3 %. The peak of occurrence of mature female was October and that of male was August to October. The prey items in stomach contents represented fish and squid. More than half of diet was squid for large individuals with ML over 30 cm. In the recent surveys, however, catches are rather poor even under similar oceanographic condition which characterized good fishing grounds in the former surveys, as noted above. Also, the mechanism affecting formation of good fishing grounds has not been clarified.