Paralarval distribution of the ommastrephid squid Todarodes pacificus during fall in the southern Sea of Japan, and its implication for locating spawning grounds

Annual fall surveys have been conducted since 1972 to determine the paralarval distribution of the ommastrephid squid Todarodes pacificus in the southern Sea of Japan. Small ring nets (45 cm diameter, 0.34 mm mesh) were towed vertically from a depth of ca 150 m to the surface to collect the paralarvae. Samples for a study covering the southern part of the Sea of Japan were collected once a month during September–November from 1974 to 1991. Samples for a separate study focusing on a smaller area near the Korea Strait were collected during October–November from 1973 to 1999. The results of both studies indicate that the paralarval distribution range expanded when stock levels were high during the early 1970s and after the late 1980s, and contracted when stock levels were low. After the stock increase that occurred in the mid-1980s, the paralarval distribution range expanded southward in October and November. We conclude that paralarval distribution patterns might be used to estimate the adult stock size.