Occurrence of sea eels of Anguilla japonica along the Sanriku Coast of Japan

Abstract

The age and migratory history of the Japanese eel, Anguilla japonica, collected along the Sanriku Coast of Japan, were examined using otolith microstructure and analysis of strontium (Sr) and calcium (Ca) concentrations. The mean Sr : Ca ratios from the elver mark to the otolith edge indicated that there were eels with several general categories of migratory history, including sea eels that never entered freshwater and others which had entered freshwater for brief periods but returned to the estuary or bay. This first evidence of the occurrence of sea eels in this northern area indicates that Japanese eels of the Sanriku Coast do not necessarily migrate into freshwater rivers.

Evidence of different habitat use by New Zealand freshwater eels Anguilla australis and A. dieffenbachii, as revealed by otolith microchemistry

“…Otoliths were then etched with 1% HCl for 60 s, stained with 1% toluidine blue and aged by counting the number of blue-stained transparent zones (Fig. 2), as reported in Graynoth (1999) and Arai et al (2003). The ages given in this study are up to the last annuli and don't include any additional daily age of less than 1 yr.…”

“…Sagittal otoliths were extracted from each fish, embedded in epoxy resin (Struers, Epofix) and mounted on glass slides. The otoliths were then ground and polished, as described by Arai et al (1997Arai et al ( , 2003. They were then cleaned in an ultrasonic bath and rinsed with deionized water prior to being examined.…”

“…'X-ray intensity maps' of both elements were made using a JEOL JXA-8900R electron probe microanalyzer as described by and Arai et al (2003). The beam current was 0.5 µA, counting time was 0.1 s, pixel size was 3 × 3 µm, the electron beam was focused on a point of 1 µm diameter, and other analytical conditions followed those for the life-history transect The Selwyn River is the largest tributary of the lake and is shown entering the northern part.…”

“…Furthermore, application of otolith Sr:Ca ratios to trace the migratory history of eels revealed otolith signatures that were intermediate to those of marine and freshwater residents of A. anguilla (Tzeng et al 1997(Tzeng et al , 2000, A. japonica , Arai et al 2003 and A. rostrata (Jessop et al 2002), and appeared to reflect estuarine residence, or show clear evidence of switching between different salinity environments. It thus appears that a proportion of eels move frequently between different environments during their growth phase.…”

Variation in the annual growth, by sex and migration history, of silver American eels Anguilla rostrata

“…The relative abundance of coastal and estuarine resident eels in North America is unknown (Haro et al 2000), but they occur from the southern United States (Hansen & Eversole 1984, Helfman et al 1984, if not further south, to the Maritime Provinces of Canada (Smith & Saunders 1955, Eales 1968, Medcof 1969 and even the Atlantic coast of Newfoundland, if brackish water coastal ponds are considered (Gray & Andrews 1971). Japanese eels with histories of sea residence and of freshwater-estuarine migration occur from the semi-tropical coastal and estuarine waters of Taiwan and southern China to the more temperate waters of southern Japan (Tsukamoto & Arai 2001 and northern Japan (Arai et al 2003), almost to the northern limit of their range (Tesch 1977), but their relative abundance is unknown (Tsukamoto & Arai 2001). The proportion of sea resident eels may increase with increasing latitude but the proportion of migratory eels shows little difference to near 35°N latitude .…”