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MIGRATORY PATTERN AND HABITAT USE OF TROPICAL EELS ANGUILLA SPP. (TELEOSTEI: ANGUILLIFORMES: ANGUILLIDAE) IN THE PHILIPPINES, AS REVEALED BY OTOLITH MICROCHEMISTRY

2007; Lee Kong Chian Natural History Museum; Issue: 14 Linguagem: Inglês

0217-2445

Alex A. Briones, Apolinario V. Yambot, Jen‐Chieh Shiao, Yoshiyuki Iizuka, Wann‐Nian Tzeng,

Fish Biology and Ecology Studies

To determine the migratory pattern and habitat use of freshwater eels in the Philippines, we analyzed the strontium to calcium (Sr:Ca) ratio of their otoliths with the use of an electron probe microanalyzer (EPMA). The changes in the otolith Sr:Ca ratios reflect the migratory pattern of the eels between different salinity gradients. A total of 22 eels were collected from the Chico and Cagayan Rivers in Northern Luzon, the Philippines. Beyond the elver stage, the migratory pattern of the eels diversified into three types as inferred by the concentrations of strontium and calcium in the otoliths: 1) Type 1 (freshwater type) represented by eight Anguilla marmorata and three A. bicolor bicolor specimens; 2) Type 2 (marine type) represented by two A. bicolor pacifica specimens; 3) Type 3a (estuarine but freshwater-favouring type) by one A. marmorata and four A. bicolor bicolor specimens and Type 3b (estuarine but marine-favouring type) by one A. bicolor bicolor and three A. bicolor pacifica specimens. The results indicated that the tropical eels in the Philippines are widely distributed in marine, brackish and freshwater environments during the growth phase (yellow stage). Through the otolith Sr:Ca ratios and microstructure analysis, it was possible to reconstruct the migratory movements of the Philippine freshwater eels from the high-saline marine environment to the low-saline freshwater environment in the rivers. This study is the first to use otolith microchemistry in tracing the migratory and environmental history of the eels in the Philippines.