ALBERT

Description: Annual catches of Todarodes pacificus in Japan have gradually increased since the late 1980s. Paralarval abundances have also been higher since the late 1980s compared to the late 1970s and mid-1980s. Here is proposed a possible scenario for the recent stock increase based on changing environmental conditions. Based on trends in annual variations in stock and in larval abundances, catches are reviewed and potential spawning areas inferred, assuming that egg masses and hatchlings occur over the continental shelf at temperatures between 15 and 23°C. Changes are then inferred in the spawning areas during 1984–1995, based on GIS data. Since the late 1980s, the autumn and winter spawning areas in the Tsushima Strait and near the Goto Islands appear to have overlapped, and winter spawning sites seem to have expanded over the continental shelf and slope in the East China Sea.

Description: High-resolution geophysical data were acquired for an investigation across a portion of Sigsbee Escarpment using an autonomous underwater vehicle (AUV Hugin 3000), which allowed mapping of the seabed and near-seafloor features in detail and large two-dimensional data sets to be collected in a short time in deep water over rugged terrain. Complex seafloor structures are revealed in the survey area. These seafloor structures include a graben fault zone, rugged escarpment faces, slump deposits, and erosional furrows. Geological morphologies occurring in the survey area are associated with salt tectonics, gravitational driven failure, and ocean bottom-current activities. The Sigsbee Escarpment in the survey area is marked by an abrupt scarp on the order of 700 m (2300 ft) and a prominent increase in seafloor gradients as much as 30deg. The Sigsbee Escarpment in the center and west of the survey area is generally scalloped, representing retrogressive slumps. The escarpment face is characterized by narrow and sharp ridges and numerous gullies. In the east of the survey area, the escarpment appears to be upturned, tilted, and eroded. A graben fault structure, representing a suture zone possibly associated with the joining of the two underlying salt sheets, is observed in the north-central survey area. In front of the escarpment, on the continental rise, a series of longitudinal furrows and slump deposits have been interpreted. The slump deposits at the base of the escarpment form aprons of sediment consisting of displaced and mixed sediments primarily of clay.