RELATIVE ABUNDANCE, SEX-RATIO AND POPULATION-STRUCTURE OF THE JAPANESE EEL ANGUILLA-JAPONICA IN THE TANSHUI RIVER SYSTEM OF NORTHERN TAIWAN

From the Gong-Shy-Tyan (GST) Stream and the Tanshui River, Taiwan, eel s ranged from 5.53 cm T.L. (elvers) to 72.5 cm T.L. Anguilla japonica accounted for 93-99%, A. marmorata 1-7% and A. bicolor pacifica less t han 1% of all eels caught. Mean eel lengths increased from 10 cm T.L. at the downstream sites to 50 cm T.L. at the upstream sites. Females m ade up 92.8% of the sex-determined eels. Population density, averaged approximately 0.14 eel m(-2) (2.42 g m(-2)) and 0.25 eel m(-2) (0.92 g .m(-2)) in downstream sites of the GST and Tanshui River, respectively , and decreased substantially with upstream distance. Eels were rarely found in the heavily polluted and dam constructed areas in the midstr eam site of the Tanshui River.