Effect of El Niño on migration and larval transport of the Japanese eel (Anguilla japonica)

Abstract

Kim, H., Kimura, S., Shinoda, A., Kitagawa, T., Sasai, Y., and Sasaki, H. 2007. Effect of El Niño on migration and larval transport of the Japanese eel (Anguilla japonica). – ICES Journal of Marine Science, 64: –. To clarify the effect of an El Niño on the migration of Japanese eels (Anguilla japonica) in the western North Pacific, differences in migration patterns of eel larvae (leptocephali) in El Niño and non-El Niño years were compared qualitatively through a numerical particle-tracking model. Depending on interannual meridional displacements of the salinity front and bifurcation of the North Equatorial Current, transport of Japanese eel larvae to the Kuroshio was much less than to the Mindanao Current in an El Niño year, and recruitment to coastal habitats in Japan decreased in those years. In non-El Niño years, transport to the Kuroshio was twice as high, and recruitment to coastal habitats increased. If the spawning area of eels was independent of El Niño, transport differences between the two currents were not clear. In the western North Pacific, mesoscale eddies also played a significant role in dispersing eel larvae and prolonging their migration. Consequently, the changing oceanic conditions associated with climate change have resulted in decreased recruitment of Japanese eels, and the eddy effect on migration of the Japanese eel larvae needs to be added into the North Equatorial Current–Kuroshio system.

Estimation of larval duration in Anguilla spp., based on cohort analysis, otolith microstructure, and Lagrangian simulations

“…Output files of Lagrangian simulations included the position (longitude, latitude, depth) and time for each particle. We established 'arrival lines' at longitude 20°W and latitude 30°N based on previous studies for Anguilla anguilla (Bonhommeau et al 2009a) and A. japonica (Kim et al 2007, Zenimoto et al 2009), respectively (Fig. 1a,b).…”

“…In the North Atlantic, OFES also reproduced fine-scale flow fields including mesoscale eddies , Masumoto 2010) and thermal structures (Doi et al 2009). Because of their high resolution and reproducibility, OFES outputs have been used for the particle-tracking calculations to estimate larval transport of the Japanese anchovy Engraulis japonicus, sardine Sardinops melanostictus (Itoh et al 2009), and Anguilla japonica (Kim et al 2007, Zenimoto et al 2009, and also to understand the temperature environment experienced by Pacific bluefin tuna Thunnus orientalis ).…”

“…The decline of both species has been caused by several factors, including overfishing (Dekker 2003), habitat degradation and loss by human activity such as constructions of dams and weirs (Feunteun 2002, Dekker 2003, Laffaille et al 2007, and fluctuations in oceanic conditions (Knights 2003, Kimura & Tsukamoto 2006, Friedland et al 2007, Kim et al 2007, Bonhommeau et al 2008a,b, Zenimoto et al 2009). For most marine species, changes in survival rate during their early life stages have a potentially significant impact on their stocks.…”

“…For this purpose, we used Lagrangian numerical simulations of larval transport and model temperature data to estimate mean larval duration and the ambient temperature regime experienced by Anguilla anguilla and A. japonica. This study aims to expand on previous knowledge of larval duration, such as the work of Kettle & Haines (2006) and Bonhommeau et al (2009b) for A. anguilla and of Kimura et al (1999) and Kim et al (2007) for A. japonica. The numbers of increments formed during the larval stage at certain ambient temperatures were estimated based on Fukuda et al (2009).…”

Discovery of a spawning area of the common Japanese conger Conger myriaster along the Kyushu-Palau Ridge in the western North Pacific

“…Therefore, the C. myriaster larvae trapped within the mesoscale eddies could be transported to the western boundary in several months, even if they were temporarily entrained into eastward currents such as the STCC. Mesoscale eddies are also considered to have an influence on the larval migration route of the Japanese eel [49], and the possible role of the directional swimming of these migrating Conger and Anguilla leptocephali to increase their westward transport is not yet known. Further studies on larval transport simulations using physical oceanographic models for the western North Pacific subtropical current system are required to elucidate the recruitment mechanism of C. myriaster, which should lead to international control of the stock management of this important fisheries resource.…”