Three gobiid fishes, Acentrogobius sp. (Japanese name: Tsumaguro-sujihaze), A. virgatulus (Sujihaze), and A. pflaumii (Moyou-haze), are widely distributed around the Japanese archipelago, and are important food resources for manycoastal fishes, including several commercial species. Despite their importance, little information has been reported on their life history traits, mainly because they were recognized as a single species “A. pflaumii” until recently. To elucidate and compare the growth characteristics and reproductive biology of the three species, we collected specimens of the three species at the same site in Maizuru Bay (one of the sub-basins of Wakasa Bay, in the Sea of Japan) every week (during the spawning season) or every month (during the non-spawning season) from 2009 to 2010. We estimated the growth characteristics and reproductive biology including life span, spawning season, pelagic larval duration, at maturing size, and spawning times, based largely on seasonal changes in length composition, gonadosomatic index (GSI), egg size, and numbers of eggs in the ovaries. The three species were found to have a similar life span (1–2 years) and pelagic larval duration (about two months), but a different spawning season (earliest and longest in A. pflaumii) and at maturing size (smallest in A. pflaumii). By comparing their reproductive traits with their distribution characteristics, we discuss the adaptive significance of the three species. Several reproductive traits of A. pflaumii (such as longer breeding season and smaller size at maturity than the other two species) may be associated with its distribution being farther offshore; larvae hatching at sites farther offshore would likely disperse more widely and experience more varied environments, and their mortality rate would probably be higher during the pelagic larval stage and atthe settlement stage.

In order to elucidate the effect of short-time variability of ocean condition on the fisheries catch, we executed intensive monitoring of sea surface temperature in the coastal water of western Kyushu Island from 2000 to 2007. The monitoring was conducted by the continuous SST recording at the four coastal stations, on-board SST measurement from a ferry boat, and CTD observation by fisheries research vessels. The SST monitoring revealed the occurrence of a sudden rise in SST in the monitored region in the early spring of 2007. With the aid of satellite infrared images, it is shown that this warm water was derived from the northern edge of the Kuroshio and propagated to this region via two routes; offshore and coastal. The warm water supplied by the offshore route formed an anti-cyclonic eddy in the central part of the Goto and Amakusa Nada, which contributed to the continuous high temperature condition in the long term over one month. The warm water with thickness of 100m supplied from the coastal path reached far north to the north part of Goto Nada. The monitoring data suggested that the propagation of warm water to western Kyushu occurred in the other monitoring season while the rise of SST would be obscure because of small temperature differences between the coastal and offshore waters.

The diel vertical migration of walleye pollock Theragra chalcogramma late larvae and early juveniles (12–32mm in body length) was examined by the acoustic method using a quantitative echosounder and net towing on two transectsin the northern Japan Sea around Hokkaido in April. Larvae and juveniles of walleye pollock were distributed at 40–80m and 20–50m depth layers during the daytime and the nighttime, respectively. They hardly migrated to the acoustic deadzone, such as near the surface and the seabed area, which allows examining the distribution pattern by acousticdata logging. The total backscattering volume (NASC: m² · NM^-2) of them for each transect was 1.1- or 1.4-times higher during the nighttime than the daytime. It would be caused by diel differences in distributional concentration of euphausiids and spatial overlap of euphausiids and pollock larvae and juveniles. During the daytime, euphausiids aggregated in swarms at the middle layer; these swarms were easily distinguishable from “pollock echograms” and we removed these swarms from the echo integrations. On the other hand, euphausiids were diffused and they overlapped with the distribution of walleye pollock at night, so it was difficult to discriminate clearly between these two organisms. Therefore, acoustic surveys to estimate the biomass of walleye pollock larvae and juveniles should be carried out in daytime.