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Marine Ecology Progress Series

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MEPS 248:237-244 (2003)  -  doi:10.3354/meps248237

Offshore entrainment of anchovy larvae and its implication for their survival in a frontal region of the Kuroshio

Yuji Okazaki1,*, Hideaki Nakata1, Shingo Kimura2, Akihide Kasai3

1Faculty of Fisheries, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan
2Ocean Research Institute, University of Tokyo, 1-15-1 Minamidai, Nakano, Tokyo 164-8639, Japan
3Graduate School of Agriculture, University of Kyoto, Kyoto 606-8502, Japan

ABSTRACT: Focusing on an incidence of coastal water entrainment into the Kuroshio frontal region, we looked at the fate of anchovy larvae Engraulis japonicus originating from coastal spawning grounds and entrained into the frontal region with the coastal low salinity water. Drifters were released in the low salinity water of the Kuroshio frontal region, and observation and sampling were conducted during drifter tracking from 18 to 21 May 1997. Naupliar copepod abundance and copepod production were high in the low salinity water at an early phase of the tracking, but decreased with elapsed days. Anchovy larvae were most abundant on the coastal side of the Kuroshio, especially in the low salinity water. Their ages estimated from otoliths were consistent with those inferred from the advective transport speed from the coastal spawning ground. The estimated biological mortality rate of first-feeding larvae (less than 7 d old) in the low salinity water was 0.71 d-1, which was high compared to rates previously reported for Engraulis spp. This high mortality could have been caused by poor nutritional conditions due to decreasing copepod production and abundance, suggesting that the offshore entrainment of fish larvae originating from coastal water could be unfavorable for their survival. The encounter with a frontal eddy would enhance food production and the subsequent survival of anchovy larvae in the frontal region; otherwise, they may perish due to low food availability.

KEY WORDS: Anchovy larvae · Offshore entrainment · Kuroshio front · Larval survival

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