Reproduction and Recruitment Success of the Japanese Common Squid, Todarodes pacificus, related to Annual and Seasonal Changes of Winter Wind Stress and Mixed Layer Depth.

点击翻译按钮获取中文摘要

Recruitment success in squids depends largely on environmental conditions at the spawning and nursery grounds. The autumn and winter spawning groups of Japanese common squid, Todarodes pacificus have the largest biomass and the annual catch of winter groups have fluctuated widely. T.pacificus produces gelatinous, nearly neutrally buoyant egg masses that contain many small eggs. The egg masses are thought to occur within or above the pycnocline at temperatures suitable for egg development (e.g., 15-23℃ in T.pacificus) and under conditions of reduced predation. After hatching, the paralarvae presumably ascend to the surface layer and are advected into convergent frontal zones We observed something resembling a T.pacificus egg mass within the pycnocline at 70-120 m depth (temperature range : 18-21℃) in the Tsushima Current using an ROV. We also estimated from laboratory studies that hatchlings ascend to the surface at temperatures of 18-23℃. We used this new reproductive hypothesis to estimate winter spawning areas of T.pacificus. Results of a previous study suggested that annual catches of T.pacificus increased during periods of weak winds and warm air temperature, suggesting that the strength of winter winds may affect recruitment. The spawning areas of winter spawning group during warm regime after 1990's were estimated to be along the continental edge off the Kyushu Island and the Nansei Islands. Inner flow of Kuroshio will transport paralarvae in surface layer from the spawning areas to the nursery areas of northeastward along the continental edge. However, the spawning areas during cool regime during 1980's were reduced along the continental edge. We can present a scenario for how stock size in T.pacificus might fluctuate due to environmental factors such as sea surface temperatures and suggest how to forecast the stock fluctuation related to climatic regime shifts and global warming.