Transport-determined early growth and development of jack mackerel Trachurus japonicus juveniles immigrating into Sagami Bay, Japan

2007 ◽  
Vol 58 (11) ◽  
pp. 1048 ◽  
Author(s):  
Songguang Xie ◽  
Yoshiro Watanabe

Oceanographic conditions and transport processes are often critical factors that affect the early growth, survival and recruitment of marine fishes. Sagittal otoliths were analysed to determine age and early growth for 381 jack mackerel (Trachurus japonicus) juveniles from Sagami Bay on the Pacific coast of Japan. Two separate hatching periods (December and February–March) were identified. They originated from the spawning grounds in the East China Sea. Early growth and developmental rates of December-hatching fish were lower than those for February–March-hatching fish. It is likely that these differences were determined in the Kuroshio Current during transport from the spawning grounds to Sagami Bay, and the lower December water temperatures in the bay. Origin and hatch dates of juveniles in Sagami Bay were in contrast to previous research on Fukawa Bay, where April-or-later-hatching fish from spawning grounds in the coastal waters of southern Japan constituted about half of the juvenile population. Management of these two jack mackerel stocks needs to consider these differences in hatch date composition and spawning origins, as these differences could affect early growth and subsequent mortality.

2011 ◽  
Vol 1 (1) ◽  
pp. 183-188 ◽  
Author(s):  
T. Ohta ◽  
Y. Mahara ◽  
T. Kubota ◽  
J. Sato ◽  
T. Gamo

AbstractWe measured the 228Ra/226Ra activity ratios in surface seawater along the Pacific coast of Japan at five ports around the island of Izu-Oshima (n = 29), at Atami in Sagami Bay (n = 13), and at Umizuri Park in Tokyo Bay (n = 14). We also conducted these measurements along a transect from the open Pacific Ocean across the Kuroshio to the mouth of Tokyo Bay (n = 7). The activity ratios decreased with increasing salinity of the sampling sites. The 228Ra/226Ra activity ratios in surface seawater along the coast gradually decreased after at the end of autumn and were lowest in winter and the beginning of spring. The surface salinity along the coast decreased from summer into autumn and increased from winter to the beginning of spring. The activity ratios decreased with the increase of salinity.The variation in activity ratios at the three coastal sites is possibly caused by differing contributions of surface seawater from the Kuroshio and surrounding open ocean. The different patterns and ranges of variation in the 228Ra/226Ra activity ratios in surface seawater at Izu-Oshima, Atami, and Umizuri Park may reflect both the amount of water from the Kuroshio and vicinity, and the local bathymetry, because continental shelf sediment is the source of Ra isotopes in surface seawater.


Author(s):  
Tomoya Horiuchi ◽  
Reiji Masuda ◽  
Hiroaki Murakami ◽  
Satoshi Yamamoto ◽  
Toshifumi Minamoto

2002 ◽  
Vol 68 (sup1) ◽  
pp. 194-197 ◽  
Author(s):  
TAKU YOSHIMURA ◽  
KENJI MORINAGA ◽  
SHIGERU SHIRAI ◽  
HIROSHI YAMAKAWA

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