Relative contribution of migratory type on the reproduction of migrating silver eels, Anguilla japonica , collected off
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ORIGINAL PAPER
Relative contribution of migratory type on the reproduction of migrating silver eels, Anguilla japonica, collected off Shikoku Island, Japan Naoko Chino Æ Takaomi Arai
Received: 29 October 2008 / Accepted: 12 December 2008 / Published online: 31 December 2008 Ó Springer-Verlag 2008
Abstract In order to understand the reproductive contribution among migratory types in the Japanese eel, Anguilla japonica, otolith strontium (Sr) and calcium (Ca) concentrations by X-ray electron microprobe analysis were examined for 37 silver eels collected in Kii Channel off Shikoku Island during the spawning migration season. The wide range of otolith Sr:Ca ratios indicated that the habitat use of A. japonica was not obligatory but facultative among fresh, brackish and marine waters during their growth phases after recruitment to the coastal areas as glass eels. Three migratory types, which were categorized as river eels, estuarine eels and sea eels were found. The estuarine eels were dominant (59%), followed by sea eels (22%) and river eels (19%). The low proportion of river eels from the spawning migration season suggested that the estuarine and sea eels inhabiting the nearby coastal areas might make a larger reproductive contribution to the next generation in this area.
Communicated by U. Sommer. N. Chino Laboratory of Ecophysiology, Graduate School of Fisheries Sciences, Kitasato University, 160-4 Sanriku, Ofunato, Iwate 022-0101, Japan T. Arai (&) International Coastal Research Center, Ocean Research Institute, The University of Tokyo, 2-106-1 Akahama, Otsuchi, Iwate 028-1102, Japan e-mail: [email protected]
Introduction The Japanese eel Anguilla japonica Temminck and Schlegel is widely distributed in East Asia, from Taiwan in the south, through eastern China and Korea, up to the Sanriku Coast of northern Honshu Island, Japan (Tesch 1977). A. japonica generally has been considered a catadromous fish species (McDowall 1988), which spawns in the north equatorial current to the west of the Mariana Islands. Their transparent leaf-like larvae (leptocephali) are transported from the spawning area toward the coastal waters of east Asia by the north equatorial and Kuroshio currents, where they metamorphose into glass eels. In general, the glass eels migrate upstream to grow into the elver and yellow eel stages in freshwater. At maturation, the yellow eels metamorphose into silver eels, which migrate downstream to the ocean to begin their spawning migration (Tesch 1977). Otolith microchemistry studies have revealed that some yellow and silver eels of temperate A. japonica never migrate into freshwater, but spend their entire life history in the ocean (Tsukamoto and Arai 2001). The application of otolith Sr:Ca ratios to trace the migratory history of eels has also revealed otolith signatures intermediate to those of marine and freshwater residents of several anguillid species (Tzeng et al. 2000; Tsukamoto and Arai 2001; Arai et al. 2003a, 2003b, 2004, 2006; Shiao et al. 2003; Kotake et al. 2003, 2005; Daverat et al
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