MEPS 261:233-242 (2003)  -  doi:10.3354/meps261233

ABSTRACT: Strontium (Sr):calcium (Ca) ratios in otoliths of the eels Anguilla japonica and A. marmorata caught in 4 Taiwanese rivers were examined to reconstruct their migratory environmental history. In all sampling locations, each eel species preferred a different environment and all were differently distributed in the river. A. japonica was more abundant than A. marmorata in the lower reach, accounting for 76 to 86% of the eel population. In contrast, A. marmorata was more abundant than A. japonica in the upper reach, accounting for 76 to 100% of the eel population. A. japonica consisted of diversified migratory contingents, including freshwater, brackish-water and seawater eels, but A. marmorata tended to reside in freshwater and seemed to avoid seawater during the yellow eel stage. This disparity in migratory behaviors and habitat use between species may reflect interspecific competition and adaptive radiation. The flexible migratory behavior and adaptation to different salinities of A. japonica may be an advantageous evolutional fitness when facing competition, heavy fishing pressure and environmental stress. The freshwater-restricted A. marmorata is more easily threatened by both fishing pressure and continuous habitat degradation than A. japonica.

KEY WORDS: Anguilla japonica · Anguilla marmorata · Otolith microchemistry · Environmental history · Migratory behaviors · Adaptive radiation