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Effect of climate changes on the larval ecology of pelagic fishes in the Pacific

PI: Hee-Yong Kim
Institution: Ehime University
Abstract:
Most of migration fishes such as Japanese eel (Anguilla japonica) and tuna (Thunnus thynnus orientalis) spawn in the tropic and the sub-tropic region where is away from a habitat of adult. Therefore, transport of their larvae which swimming ability is weaker than the current velocities by the ocean circulation in a scale of the North Pacific plays a significant role in an entire life history. Thus the migration fish with the long passive larval stage such as Japanese eel is largely exerted on by the effect of physical dispersion bringing about large early decrease of their population.

In case of the Japanese eel which is a representative species whose spawning grounds is far away from the nursery grounds, it is thought that some of them having searched more efficient transport processes for survival generate a present migration system adapted to the current system from tens thousands or hundreds thousands years. Thus the roles of currents for the differentiation and the dispersion of species are very significant and the present migration path from the spawning ground to the nursery ground will not change if the currents are steady state. However, oceanic structures including the present currents system not only have fluctuated seasonally/inter-annually but also have been affected by ocean-climate changes such as the El Niño with some years scale and a decadal regime shift. Not only the larval transport paths but also the spawning behavior of the adults has been varied according to these fluctuations of the oceanic structures, which also have caused the fluctuation of fisheries resources.

Fisheries resources of Japanese eels, and Atlantic eels, which are a closely related species and habitats in the Atlantic, have decreased since around 1975 when showed a peak of catches. An ocean-climate change with the earth scale known as climate regime shift occurred in 1975. After that, El Niño have happened in the short run term, and on a long term basis the position of salinity front closely related to the spawning behavior of Japanese eel have gradually shifted to the north. Spawning area of Japanese eel is located in the North Equatorial Current west of Mariana Islands as shown in Fig. 1 (Tsukamoto, 1992). They are firstly transported from the North Equatorial Current (NEC) region and then to the coast of Japan by the Kuroshio from near the Luzon Strait (Fig. 1) (Kimura et al., 1994). The positions of salinity front, considered as an indicator of spawning behavior of Japanese eel, due to the NEC are affected by the occurrence of the El Nino events (Kimura et al., 2001), and the fluctuation of the NEC dominates the success and failure of larval transport.

Therefore, Firstly, we have to understand the generation properties of Ocean-Climate changes in the Pacific and the Atlantic using several statistics data, and then getting hold of the changes of oceanic structures in the two oceans when these ocean-climate changes, particular El Niño and non- El Niño events. the output from the IPCC simulations is thought to provide us with many imformations of climate changes in the scale of the Pacific.
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    Lawrence Livermore National Laboratory  |  Physical & Life Sciences Directorate