A combination mode of climate variability responsible for extremely poor recruitment of the Japanese eel (Anguilla japonica)

Yong-Fu Lin,Chau-Ron Wu,Yu-San Han

doi:10.1038/srep44469

Abstract

Satellite data and assimilation products are used to investigate fluctuations in the catch of Japanese eel (Anguilla japonica) in eastern Asian countries. It has been reported that the salinity front has extended farther south, which has shifted the eel’s spawning grounds to a lower latitude, resulting in smaller eel catches in 1983, 1992, and 1998. This study demonstrates that interannual variability in the eel catch is strongly correlated with the combination mode (C-mode), but not with the El Niño–Southern Oscillation. These eels continue to spawn within the North Equatorial Current (NEC), but the salinity front shifts south during a canonical El Niño. On the other hand, the spawning grounds accompanied by the salinity front extend farther south during the C-mode of climate variability, and eel larvae fail to join the nursery in the NEC, resulting in extremely poor recruitment in East Asia. We propose an appropriate sea surface temperature index to project Japanese eel larval catch.

Highlights

Satellite data and assimilation products are used to investigate fluctuations in the catch of Japanese eel (Anguilla japonica) in eastern Asian countries
This study demonstrates that interannual variability in the eel catch is strongly correlated with the combination mode (C-mode), but not with the El Niño–Southern Oscillation
The spawning grounds accompanied by the salinity front extend farther south during the C-mode of climate variability, and eel larvae fail to join the nursery in the North Equatorial Current (NEC), resulting in extremely poor recruitment in East Asia

Summary

Seasonality of the salinity front

The sea surface salinity (SSS) distribution is closely related to the precipitation pattern and significantly modulated by the Inter-tropical Convergence Zone (ITCZ)[7]. The rainfall zone (or the ITCZ) in Fig. 4b is farther south compared with that, in the northwestern tropical Pacific where potential Japanese eel spawning grounds are located During these extreme events, the ITCZ moves significantly southward and may cross the equator, which leads to dramatically reduced precipitation in the northwestern Pacific, and the salinity front can extend south of the equator (Fig. 3a). The SST anomaly in the warm pool precedes the precipitation anomaly (i.e. position of ITCZ) by 0–4 months, while negative peaks in the precipitation anomaly precede the SSS maxima (i.e. extreme southward movement of the salinity front and spawning ground) by 6 months, affecting the Japanese eel catch significantly. One could expect poor recruitment in East Asia 6 months before intense cooling is observed in the northwestern Pacific warm pool

Conclusion

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Additional Information