Migratory history and habitat use of Japanese eel Anguilla japonica in the Sanriku Coast of Japan

Abstract

The migratory history of the Japanese eel Anguilla japonica collected in Otsuchi Bay and the adjacent stream along the Sanriku Coast of Japan was examined using otolith microchemical analysis of strontium (Sr) and calcium (Ca) concentrations. X‐ray intensity maps of Sr concentration in the otoliths showed that all specimens generally had a high Sr core at the center of the otoliths, which corresponded to the period of leptocephalus and early glass eel stages in the ocean, while line analysis of Sr : Ca ratios along the life‐history transect of each otolith showed a peak (≈ 13–20 × 10−3) between the core and elver mark. The mean Sr : Ca ratios from the elver mark to the otolith edge indicated eels of several general categories of migratory history, including sea eels that never entered freshwater (average Sr : Ca ratios > 6.0 × 10−3) and estuarine eels that entered freshwater for brief periods, but returned to the estuary or bay (average Sr : Ca ratios 2.5–6.0 × 10−3). This evidence of the occurrence of several migratory patterns in this northern area indicates that A. japonica has a flexible pattern of migration, with an ability to adapt to various habitats and salinities. Thus, migrations of anguillid eel into freshwater are facultative and not obligatory.

Stable isotope analyses provide new insights into ecological plasticity in a mixohaline population of European eel

“…Eels were originally thought to make an obligate migration into freshwater to fulfil their catadromous life cycle. However, the development of high-resolution otolith Sr:Ca techniques (Thresher 1999), has allowed workers to track the migration histories of individual eels from otolith microchemistry and has shown that an eel stock may include several divergent migratory components, where some individuals may complete their life cycle without entering freshwater, and may reside in marine or brackish waters till maturation (Tsukamoto et al 1998;Tzeng et al 2000;Tsukamoto and Arai 2001;Jessop et al 2002;Tsukamoto et al 2002;Arai et al 2003;Shiao et al 2003;Tzeng et al 2003;Jessop et al 2004). It has become apparent that the so-called freshwater eels can actually make significant use of marine and mixohaline habitats (Tsukamoto and Arai 2001;Tsukamoto et al 2002), and Tsukamoto et al (1998) even suggested that marine eels might form the bulk of the spawning stock.…”

The inclusion of sub‐detection limit LA‐ICPMS data, in the analysis of otolith microchemistry, by use of a palindrome sequence analysis (PaSA)

“…Microscopic daily increments in the otoliths are routinely and extensively used to infer pelagic duration, larval size-at-age, and pre-and post-settlement growth rates (Thorrold and Hare 2002). Moreover, the chemical composition of otoliths is increasingly used to identify natal grounds, migratory routes, and larval dispersal trajectories (Swearer et al 1999;Arai et al 2003a;Rooker et al 2003;Arai and Morita 2005;Patterson et al 2005;Sandin et al 2005). The latter use of otoliths has generated considerable excitement and effort, since it potentially opens a window on the mysteries of larval dispersal.…”

Habitat residence during continental life of the European eel Anguilla anguilla investigated using linear discriminant analysis applied to otolith Sr:Ca ratios

“…This allowed us to develop a method based on LDA for reliable assignment of all Sr:Ca values corresponding to fish continental life in a specific environment (BW versus FW). Most studies on eel migratory behaviour using Sr:Ca have relied on empirical descriptions of the Sr:Ca variation only, with no statistical treatment of the signal (Tzeng et al 1999, 2002, Arai et al 2003, Tzeng 2003. The use of LDA for habitat assignment of otolith spots in the present work allowed us to overcome some technical issues commonly faced when using Sr:Ca to reconstruct fish migrations between habitats with varying salinities (Jessop et al 2007(Jessop et al , 2008.…”