Distinct impacts of the 1997\u201398 and 2015\u201316 extreme El Ni\xf1os on Japanese eel larval catch

Yong-Fu Lin,Chau-Ron Wu

doi:10.1038/s41598-018-37569-5

Abstract

Extraordinarily poor recruitment of Japanese eels in East Asia has been generally reported during extreme El Niño years. However, the scenario failed to take place during the 2015–16 extreme event. In this study, we examined possible factors responsible for differing eel abundance in East Asia during the two strongest recent extreme El Niños, which occurred in 1997–98 and 2015–16. Numerical tracer experiments were carried out to determine why the impacts on eel catches seen in 1997–98 were not repeated in 2015–16. Among physical factors, two scenarios are likely responsible for extremely poor recruitment in East Asia: southward migration of the North Equatorial Current (NEC) or southward movement of eel spawning grounds. Comparing the latitudinal shift of NEC locations between the 1997–98 and 2015–16 El Niños, we conclude that NEC migration may be a factor, but is not chiefly responsible, for lower eel catches. Our findings pointed to southward movement of spawning grounds as the dominant factor. The northward movement of spawning grounds during 2015–16 meant that eel larvae were preferentially transported into the NEC-Kuroshio system, which resulted in a higher rate of recruitment success. The distinct evolution and dynamics of these two El Niño events led to different spawning ground locations, impacting eel abundance in East Asian countries.

Highlights

Japanese eels traverse thousands of kilometers over several months to spawn around 12–15°N, south of the salinity front in the North Pacific (34.5 PSU)[1,2,3,4]
The 2015–16 extreme El Niño did not result in extremely poor recruitment of Japanese eel in East Asia, as have other extreme El Niños
Rather than southward migration of the North Equatorial Current (NEC), the present study demonstrated that southward movement of eel spawning grounds was mainly responsible for lower eel catches

Summary

Physical Factors Responsible for Poor eel Catches

Collective wisdom points to two factors most likely responsible for extremely poor Japanese eel recruitment in East Asia: southward migration of the NEC8 or southward movement of eel spawning grounds[7]. The eel spawning grounds that accompany the salinity front extended farther south beyond the NEC in 1997 (south of 11°N, Fig. 3a), and newly hatched larvae cannot be successfully carried by the NEC, leading to extraordinarily diminished eel catches in East Asian countries. We conducted two simulated tracer experiments with the same ocean currents to better understand the effect of a latitudinal shift in spawning locations on the recruitment success of the Japanese eel. The eel larvae were preferentially transported into the Kuroshio with a higher successful recruitment rate in EX2 (18.4%), resulting in relatively high recruitment in East Asia

Distinct dynamics of the two types of El Niño

Conclusion

Methods

Findings

Additional Information