The salinity front in the North Equatorial Current: A landmark for the spawning migration of the Japanese eel (Anguilla japonica) related to the stock recruitment

A synthesis of the ecological processes influencing variation in life history and movement patterns of American eel: towards a global assessment

“…Critical gaps in scientific knowledge (Stone 2003) have prevented a thorough analysis of the population dynamics of this species and a confident separation of the relative effects of anthropogenic and natural sources of mortality. Similar declines (in magnitude and time period) observed in populations of European (A. anguilla) and Japanese (A. japonica) eel (Castonguay et al 1994b;Moriarty and Dekker 1997;Stone 2003;Tatsukawa and Matsumiya 1999) suggest that global oceanic changes are similarly and simultaneously affecting these species (Knights 2003;Kimura and Tsukamoto 2006;Friedland et al 2003), that human activities have exerted similar pressure on continental and marine life stages of all eels (Haro et al 2000;Feunteun 2002;Dekker 2003), or that both factors may be involved. For instance, declines in the size of glass American eel arriving to the coastal United States (Sullivan et al 2006), which might negatively influence first year survival (Sogard 1997), could be an important indicator of oceanic environmental factors operating at large geographic scales.…”

“…Significant negative correlations have been found between the NAO and long-term catches of A. anguilla, probably due to reduced larval survival attributed to warming of the spawning area, declining winds related to larval transport, and shallowing of the mixed layer depth where larvae feed (Friedland et al 2003). Similarly, declining larval survival in A. japonica has been linked to El Niño and associated northward advance of salinity fronts (Kimura and Tsukamoto 2006). The distribution and dispersal of American eel along the North Atlantic coast depends directly on the strength and position of the Gulf Stream (Wirth and Bernatchez 2003), partly because most leptocephali enter the Gulf Stream directly from the Sargasso Sea rather than by a more southern route through the Bahamas (Kleckner and McCleave 1982).…”

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

“…Based on the molecular phylogenetic relationships of anguilliform fishes, conger eels and freshwater eels evolved through different lineages, even though their general body morphologies are quite similar, so conger eels appear to be most related to the shelf and slope eels of the Nettastomatidae and may have retained characteristics of deep-benthic eels such as the cutthroat eels of the Synahobranchidae, while freshwater eels are most related to the midwater pelagic deep-sea eels such as the gulper eels of the Eurypharyngidae and the saw-tooth eels of the Serrivomeridae [37]. However, further studies are needed to determine the larger-scale distribution of spawning and to learn about possible latitudinal cues for spawning, such as fronts [38] or current flows, which have been suggested to be important in determining the locations of Japanese eel spawning [25,39].…”

“…Since the spawning area of the Japanese eel was found to occur along the West Mariana Ridge within the latitudes of the main part of the NEC (12-14°N) [22][23][24][25], with their larvae being transported westward by the NEC and then transferring to the Kuroshio to recruit to East Asia [39,[44][45][46], it appears that C. myriaster has a slightly different spawning and recruitment strategy. It has also been estimated that C. myriaster larvae are transported westerly Fig.…”

Ontogenetic changes in phototactic behavior during metamorphosis of artificially reared Japanese eel Anguilla japonica larvae

“…Kimura et al (1994) hypothesized that this distribution in shallower depths enables leptocephali to use the slight northward flow caused by Ekman transport resulting from the trade winds in the region; this would help them transfer between the currents when they come up to the surface layer at night. This vertical migration of leptocephali at this stage of their life history may be critical in enabling them to avoid being transported beyond their species' range when the NEC bifurcates into the Kuroshio Current and the southward-flowing Mindanao Current (Kimura et al 1994, Kimura & Tsukamoto 2006. Diel vertical migration is also observed in a wide range of both freshwater and marine zooplankton taxa (Lampert 1989, Hays 2003, Pearre 2003 and is a complex phenomenon affected by many endogenous and exogenous factors such as light, trophic state, buoyancy, hydrostatic pressure, salinity, temperature, water movement and circadian rhythms (Crisp 1974, Stancyk & Feller 1986, Naylor 2006.…”