북서태평양 대륙주변부해역 살오징어(Todarodes pacificus) 자원생태학적 연구

Abstract

This study focused on the fluctuation in the catch of the common squid, Todarodes pacificus Steenstrup by artificial-natural environmental factors in the northwest Pacific Marginal Seas. Especially, impacts of climate changes on the entire life cycle of common squid were discussed. Also, existence of the spawning ground in Korean waters caused by climate changes was discussed. The common squid distribute in the northwestern Pacific has been fluctuated. This fluctuation is caused by 2 factors in general: artificial factors and natural environmental factors. Data of the total catch, catches by the Korean jigging fishery and catches by different fishing methods in the common squid and the number of the Korean jigging fishery boats and auto fishing machines were collected to understand artificial factors. The fluctuation in the total catch of the common squid is similar pattern with fluctuations of the number of the Korean jigging fishery boat and auto fishing machine. However the fluctuation in the total catch for the common squid is not similar pattern with the fluctuation of CPUE (catch per boat). Data of water temperature by depth inferred from SST (sea surface temperature) were picked out from NOAA/AVHRR (1981.07-2002.12) and MODIS/AQUA (2003.01-2009.12) were collected to understand spawning ground environment changes are one of natural environmental factors. Salinity data (1980-2009) from WOD09 and surface current data (1980-2009) from AVISO were collected to infer transport paths of eggs or paralarvae of the common squid. Also, major 5 climate indices, East Asia Winter Monsoon Index (EAWM), Siberian High Index (SH), Arctic Oscillation Index (AO), Pacific Decadal Oscillation (PDO) and Aleutian Low Pressure Index (ALP), influence the northwestern Pacific were used to study relationship spawning ground environment changes pattern with climate forcing. The size of spawning ground was larger after the 1990s than the 1980s, while the size of spawning ground in the East China Sea was smaller the 1990s than the 1980s and the 2000s in autumn because of increasing water temperature in the 1990s. Current changes in the East China Sea made more influx of warm water to the west sea in the 1980s and the 2000s than the 1990s. There was relationship between current changes and the fluctuation in total catch of the common squid in the west sea. Also, current path changes coincided with PDO phase since 1980. Data of commercial catch for the common squid by monthly and district in 1970-2010, catch by the Korean jigging fishery by 0.5。 latitude×0.5。 longitude grids, 1980-2009 and water temperature in KODC, 1980-2009, were collected to understand changes of distributions and migrations which are the other of natural environmental factors. The pattern of fishing time was earlier at the 1990s and 2000s than the 1980s. It estimated that the autumn spawning cohort ratio increased than the winter spawning cohort ratio. The monthly change of the center of fishing ground was larger in the East Sea than in the west sea. Centers of fishing ground were located with near Yamato bank in the 1980s while southern part of the Ulleung Island in the 1990s and in southwestern part of the East Sea in the 2000s in December in the East Sea. The fishing ground in the 1980s, poor fishing period, stayed longer than the 1990s and the 2000s in relatively high latitude area, near Yamato bank, July - December. However, the fishing ground in after the 1990s, good fishing period, was formed in southern part of the Ulleung Island, September - January. This means that the winter cohort was dominant corhort in the 1980s migrated later than the autumn cohort was dominant corhort in the 1990s and the 2000s. Climate changes influence not only fishing time and fishing ground but also spawning ground. The study of distributions of paralarvae of the common squid was conducted to reveal the spawning ground's existence in Korean waters cause of the northward shift of the spawning ground by climate forcing. Paralarvae of the common squid were sampled with the bongo net (diameter: 60cm, mesh: 333㎛) by using oblique tow method with oceanographic research vessel Tamgu 20 at 8 stations along the central Yellow Sea and at 15 stations along the northeastern East China Sea in August, 2013 and the oceanographic research vessel Tamgu 12 at 21 stations along the southwestern coastal waters of the East Sea in June, August, September and November, 2013 and April, May, June, August and September, 2014. As a result, there is no paralarva in the central Yellow Sea and paralarva were collected 1 indivisual the northeastern East China Sea in August, 2013. Paralarvae were collected 15 ind. in 2013 and 24 ind. in 2014 in the southwestern coastal waters of the East Sea. Paralarvae were sampled at 70m to 500m bottom depth in the East Sea, approximately. Mantle length of paralarvae was from 1.7 to 13.5mm. Paralavae were distributed mainly in offshore stations in study period, horizontally. Optimum embryo survival temperature (18-24℃) was formed shallower than 60m depth for almost stations where paralarvae were existed, and survival temperature (15-24℃) for embryo stage was located shallower than 75m.