Variability of the Pacific North Equatorial Current and its implications on Japanese eel (Anguilla japonica) larval migration

Abstract

The zonal velocity produced by a Regional Ocean Modeling System (ROMS)‐based Pacific Ocean circulation model was validated against in situ measurements along the 137°E longitude. The Pacific model successfully reproduced the position and the shape of the North Equatorial Current (NEC) as well as the latitude of maximum surface velocity in the NEC region (8–17°N). The flow field produced by the Pacific model was then used to conduct numerical Lagrangian experiments, in which passive particles were released along a transect (142.5°E, 12.5–17°N) that traverses the known Japanese eel spawning area, and the effects of NEC strength and bifurcation latitude on the particle advection in the northwest Pacific were studied. Our results suggest that, in the 20‐yr period (1993–2012), the variability of the currents alone can cause interannual variability of one order of magnitude in the Kuroshio Entrance (KE), the percentage of particles entering the Kuroshio, the range of which varies from 43% in 1997 to 6% in 2012. The yearly‐averaged KE is not sensitive to the NEC bifurcation latitude. Instead, it is controlled by the average zonal velocity of a fixed domain (125–143°E, 13.5–17°N) and related to a recently‐developed climate index, the Philippines–Taiwan Oscillation (PTO). During the positive phase of the PTO, the zonal velocity in the domain, hence the yearly‐averaged KE, increases, and the opposite is true in the negative phase of the PTO. Considering only the trajectories, diel vertical migrations (DVM) in the top 400 m do not significantly affect Japanese eel larval transport, as incorporating DVM schemes does not increase the KE.

Population status and distribution of whitespotted conger (Conger myriaster) in Yellow Sea: An important migratory species along coastal China with limited data

“…Conversely, the abundance of conger showed a reduction in El Niño year in May 2015. These results implied that the climate variability (such as El Niño and La Niña) and the subsequent changes in the strength of currents and the abundance of nutrients were probably the critical factors that affected the larval transport of this long‐distance migratory fish, which was consistent with the similar studies for Japanese eel ( Anguilla japonica ), European eel ( Anguilla anguilla ), and American eel ( Anguilla rostrata ) (Egg, Mueller, Pander, Knott, & Geist, ; Han et al, ; Hsu, Xue, Chai, Xiu, & Han, ; Kim et al, ; Rypina, Kirincich, Lentz, & Sundermeyer, ; Wu, Wang, Lin, & Chao, ). However, most oceanic phenomena present decadal variations in both regional and global scales, which explains the insignificant influence of climate variability on the population dynamics of whitespotted conger owing to the limitation of time series length in this study (Han et al, ; Tuo et al, ).…”

Observation of a Gelatinous Octopod, Haliphron atlanticus, along the Southern West Mariana Ridge: A Unique Cephalopod of Continental Slope and Mesopelagic Communities

“…Examination of the hydrographic data collected by the submersible and comparison to the hydrographic sections plotted from 5 X-CTD deployments crossing through the study area indicated that it was in a zone with very gradual temperature decreases with depth and minimal salinity changes (34.4 from ∼300-800 m) below the high-salinity layer of Subtropical Underwater (STUW), which is a typical feature of this area (see [53]) (Figure 4). The latitude of the observation was within the main part of the westward flow of the North Equatorial Current [54,55].…”

Potential impact of ocean circulation on the declining Japanese eel catches

“…Overfishing and habitat loss due to human activities were considered to be one of the primary reasons causing the eel recruitment decline 7 . Changes in ocean circulation or oceanic conditions may also significantly affect eel recruitment 8 – 15 , or both types of factors have likely contributed 16 .…”

“…The migration process of Japanese eels, however, is not well understood due to limited direct observational evidence on adult migration 23 or larval dispersal 24 . Numerical modelling methods, therefore, have been used to simulate the potential migration paths of Japanese eels, and to evaluate their linkages to ocean-atmosphere changes 12 , 14 , 15 , 25 , 26 .…”

“…For example, some studies suggested that the transport of larvae carried by currents from the NEC to the Kuroshio is lowest in the El Niño years compared to the non-El Niño periods 11 , 12 . Other recent modelling studies evaluated the interannual migration success of Japanese eel larvae from their spawning area to East Asia and suggested that more complex ocean circulation factors related to the NEC, Kuroshio, and eddies can impact the migration, which are connected to the Philippine-Taiwan Oscillations (PTO) 14 , 15 . The strength and position of the NEC appear to be important factors 14 , 15 , 27 , and tropical rainfall affecting the position of the salinity front that can form in the spawning area may also affect recruitment in some years 27 .…”