Studies on the juvenile Japanese sea bass in the Chikugo estuary of Ariake Bay. Changes in distribution pattern and condition coefficient of the juvenile Japanese sea bass with the Chikugo River ascending.

Abstract

The changes in the distribution pattern and the condition coefficient with the ascending pro gress of the juvenile Japanese sea bass were examined.In the Chikugo River estuary of Ariake Bay, surface towing by a larva net was performed from March to April. A total of 5314 postlarvae and juveniles (SL, were collected by 183 tows. The body depth ratio and condition coefficient increased in proportion to the growth up to 20 mm length.As the research proceeded, the mode of the distribution moved from higher to lower salinity.The concept of distance was introduced to the temporal changes in catch of the sea bass and salinity.In mid March, sea basses were mainly distributed in the sea water area. In mid April, half the number had already reached the fresh water area, and they had condition coefficient remarkably increased. Sudden change in catch when the tide is at turn, and more catch during rising than ebbing tide were ob served. Preliminary notes on the ascending mechanism of the sea basses were given.

Influence of spring river flow on the recruitment of Japanese seaperch <em>Lateolabrax japonicus</em> into the Chikugo estuary, Japan

“…Day-to-day variability in the Japanese seaperch abundance in the Chikugo River seems to be small in late March. Our intensive (every 4 to 6 days) sampling in spring 2005 revealed that seasonal change in Japanese seaperch abundance was dome-shaped, with a peak in late March (Shoji et al, 2005a) indicating a peak in recruitment into the river at this time, as pointed out in previous studies (Matsumiya et al, 1981(Matsumiya et al, , 1982(Matsumiya et al, , 1985. Since the net was not equipped with a flowmeter during the samplings in several years from 1990 to 2000, the mean number of larvae and juveniles collected by the 14 tows (No.…”

“…Larval and juvenile Japanese seaperch dominate the ichthyoplankton community in March around the estuarine turbidity maximum (ETM) of the Chikugo River, upper Ariake Bay (Matsumiya et al, 1982). The importance of the ETM zone is widely recognised in estuaries of different parts of the world because it serves as a predation refuge for fish during the early life stages due to the high turbidity, and as their feeding ground due to the high prey concentration (e.g.…”

Migration of Japanese temperate bass Lateolabrax japonicus juveniles within the Chikugo River estuary revealed by δ13C analysis

“…All stations except the 2 uppermost were the same as 7 stations employed in previous studies (e.g. Matsumiya et al 1982Matsumiya et al , 1985. Since the ETM is usually found in the lower salinity area (<10) and transported back and forth over a 20 km range along the estuary during spring tides (Shirota & Tanaka 1981), spatial distributions within the estuary could be more easily understood in relation to salinities than stations.…”

“…In the Chikugo River estuary of the Ariake Sea on Kyushu Island, Japan, variations in migratory pathways for simultaneously occurring juveniles have been reported: some migrate upstream to the upper estuary, while others reside in the lower estuary (Matsumiya et al 1982(Matsumiya et al , 1985 or the littoral zone (Hibino et al 2002. For early juveniles of Japanese temperate bass, upstream migration has never been reported anywhere in Japan except for the Ariake Sea.…”

Use of Otolith Microanalysis to Determine Estuarine Migrations of Japanese Sea Bass <i>Lateolabrax japonicus</i> Distributed in Ariake Sea

“…As advanced-stage juveniles and adults, sea bass exhibit seasonal immigration and emigration between estuarine and deeper coastal waters. 3) Based upon field surveys of larvae and juveniles in the Chikugo River estuary (Fukuoka Prefecture, Kyushu), Matsumiya et al 4,5) proposed that the life cycle of Ariake Sea L. japonicus (named Ariake sea bass, in the present paper) has an obligate freshwater juvenile stage. Annual field surveys revealed that up-estuary dispersal with in creasing size occurred during March and April for late stage larvae and very early stage juveniles.…”