Estimation of seasonal spawning ground locations and ambient sea surface temperatures for eggs and larvae of Pacific saury (Cololabis saira) in the western North Pacific |
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| Authors: | MASAYUKI IWAHASHI YUTAKA ISODA SHIN-ICHI ITO YOSHIOKI OOZEKI SATOSHI SUYAMA |
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| Institution: | Graduate School of Fisheries Science, Hokkaido University, Hakodate, Hokkaido 041-8611, Japan; Tohoku National Fisheries Research Institute, Shiogama, Miyagi 985-0001, Japan; National Research Institute of Fisheries Science, Yokohama, Kanagawa 236-8648, Japan; Hachinohe Branch, Tohoku National Fisheries Research Institute, Hachinohe, Aomori 031-0841, Japan |
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| Abstract: | Since there have been practically no surveys of the eggs of Pacific saury (Cololabis saira) in the western North Pacific (WNP), its spawning ground (SG) distribution has been poorly resolved, based mainly on the larval distribution. This means of estimating SG distribution is imprecise because saury eggs drift for more than a week before they hatch, in a region with intense western boundary currents and their extensions. To improve our understanding of the immature saury, a large number of larvae (body length <25 mm) collected in the WNP during 1993–96 were numerically backtracked to take into account the advection by geostrophic and wind‐forced Ekman currents, and the SG locations and ambient sea surface temperatures (SSTs) for the eggs and larvae on the backtracking trajectories were estimated. The resulting seasonal distributions of SGs indicated that both the locations and the intensities of spawning change from season to season. Moreover, the ambient SSTs for eggs just after fertilization ranged from a high of around 21.5°C in early autumn (September to October) to a low of around 15.0°C in late spring (May to June) with an intermediate of around 20.0°C in winter (January to February). The ambient SSTs showed seasonally different gradients while the individuals developed from eggs to early larvae: the SSTs decreased throughout the autumn (September to December), stayed rather constant in winter (January to February), and increased throughout the spring (March to June). The ambient SSTs for the early larvae were at around 19.0°C in autumn and winter (September to February) and around 16.5°C throughout the spring (March to June). |
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| Keywords: | ambient sea surface temperatures eggs and larvae geostrophic and wind-forced Ekman currents numerical backtracking Pacific saury spawning ground locations |
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