噴火湾におけるソウハチCleisthenes pinetorum 仔魚の摂餌強度と年級群強度

抄録

To understand how strong year classes of pointhead flounder Cleisthenes pinetorum have occurred in Funka Bay, Japan, larval density, initial feeding intensity, initial prey density, oceanic conditions, and the age distribution of mature and immature flounders were investigated for several years. The proportions of collected numbers of mature and immature flounders in the 2001 and 2005 year classes were higher than those in the 2002, 2003, 2004, and 2006 year classes. A previous paper reported abundant densities and a wide variety of developmental stages (stages A-F) of pointhead flounder larvae collected with a plankton net in August 2001 compared to low and a narrow range of stages (stages A-B) collected in 2002-2003. This paper reports a similar phenomenon: abundant and numerous stages in September and October 2005 (stages A-G) but not in 2004 and in 2006 (stages A-D). Therefore, year class strength appears to relate mainly to mortality during the early larval stages. Horizontal hauls collected with a ring net in Funka Bay showed that pelagic larvae occurred within a water temperature range of 3.8-19.1℃ at 30m depth. First feeding larvae (stage A) had a relatively low feeding intensity(≤0.5 prey larva^-1) under low water temperature (≤12.0℃) conditions. The results of this study suggest that both relatively high mean water temperature between June and October and inflow of the Tsugaru Warm Current, which transports larvae to the nursery area in the bay and contributes feeding success, are necessary to produce a strong year class of pointhead flounder.