Impacts of Interannual Ocean Circulation Variability on Japanese Eel Larval Migration in the Western North Pacific Ocean

Abstract

The Japanese eel larvae hatch near the West Mariana Ridge seamount chain and travel through the North Equatorial Current (NEC), the Kuroshio, and the Subtropical Countercurrent (STCC) region during their shoreward migration toward East Asia. The interannual variability of circulation over the subtropical and tropical regions of the western North Pacific Ocean is affected by the Philippines–Taiwan Oscillation (PTO). This study examines the effect of the PTO on the Japanese eel larval migration routes using a three-dimensional (3D) particle tracking method, including vertical and horizontal swimming behavior. The 3D circulation and hydrography used for particle tracking are from the ocean circulation reanalysis produced by the Japan Coastal Ocean Predictability Experiment 2 (JCOPE2). Our results demonstrate that bifurcation of the NEC and the strength and spatial variation of the Kuroshio affect the distribution and migration of eel larvae. During the positive phase of PTO, more virtual eels (“v-eels”) can enter the Kuroshio to reach the south coast of Japan and more v-eels reach the South China Sea through the Luzon Strait; the stronger and more offshore swing of the Kuroshio in the East China Sea leads to fewer eels entering the East China Sea and the onshore movement of the Kuroshio to the south of Japan brings the eels closer to the Japanese coast. Significant differences in eel migration routes and distributions regulated by ocean circulation in different PTO phases can also affect the otolith increment. The estimated otolith increment suggests that eel age tends to be underestimated after six months of simulation due to the cooler lower layer temperature. Underestimation is more significant in the positive PTO years due to the wide distribution in higher latitudes than in the negative PTO years.

The ecology of oceanic dispersal and survival of anguillid leptocephali

“…The anguilliform swimming mode is highly efficient according to studies on migration-stage silver eels (van Ginneken et al 2005), so swimming by leptocephali may also be very efficient. Although consideration that late-stage leptocephali of anguillid and other eels may use directional swimming to reach recruitment areas like other kinds of fish larvae (Leis 2002(Leis , 2006 is at an early stage of evaluation, if they can use directional swimming it would likely have a profound effect on recruitment success as indicated by modelling studies (Rypina et al 2014;Chang et al 2015).…”

“…Based on the factors considered here, there presently is little evidence that larval survival of the later stages of leptocephali are important drivers of anguillid recruitment success. One possible exception is that the Japanese eel must entrain into the correct current flow in the NEC bifurcation zone (Kimura et al 2001;Zenimoto et al 2009;Chang et al 2015).…”

“…The most recent study on A. japonica found that the PhilippinesTaiwan Oscillation (PTO), which is an oscillation of the thermocline depth between the areas east of the Philippines or Taiwan that affects the NEC latitude and its bifurcation, had an important effect on larval recruitment (Chang et al 2015). During positive PTO years, the thermocline rises to the east of the Philippines and deepens to the east of Taiwan.…”

“…Modelling studies show that directional swimming may be important for successful recruitment (Rypina et al 2014;Chang et al 2015), and coral reef larvae that were historically thought to passively drift towards their recruitment areas are now known to use oriented swimming (Leis 2002(Leis , 2006. There is no way to clearly evaluate if large A. anguilla leptocephali swim to reach Europe or North Africa due to the complexities of otolith aging (deposition may stop at low temperatures) and transport modelling studies (Bonhommeau et al 2010;Zenimoto et al 2011).…”

Recent Advances in Japanese Fisheries Science in the Kuroshio-Oyashio Region through Development of the FRA-ROMS Ocean Forecast System: Overview of the Reproducibility of Reanalysis Products

“…Assimilated data have been analyzed instead of observed data to clarify the linkage between fish abundance and oceanographic conditions [18], and they have been used for stock management applications [19]. Survival, growth, migration, and recruitment of important commercial fish have been examined by using particle-tracking models and individual-based models (IBMs) with assimilated oceanographic conditions (e.g., [20] [21] [22] [23]). Several studies have developed high-resolution nested ocean models with data assimilation products (e.g., [24]) in an effort to understand and predict the sudden occurrence of harmful marine organisms such as jellyfish, toxic algae, and viruses.…”