Effects of Shrimp Net and Cultured Eels on the Wild Population of Japanese eel Anguilla japonica in Kao-Ping River, Taiwan

漁具和逃逸養殖鰻對台灣高屏溪下游日本鰻族群結構的影響

林裕嘉(Yu-Jia Lin) ； 曾萬年(Wann-Nian Tzeng)

《臺灣水產學會刊》 35卷1期 (2008/03) Pp. 61-73

https://doi.org/10.29822/JFST.200803.0005

摘要

To understand the effects of fishing gears and escaped cultured eels on the Japanese eel (Anguilla japonica) population in the Kao-Ping River, sex ratio and size composition of the eel caught by traditional eel tube and introduced shrimp net were investigated during the period from 1999 to 2006.Female eels were dominated in the catch before 2003 (＞70%) but significantly decreased to less than 60% in 2004 because of the cultured eels escaped from the pond. The median length and 95% length range of the eels caught by eel tubes was larger and narrower than that by shrimp nets, indicating that the selectivity differed between fishing gears. The percentage of eels less than 400 mm increased in the catch since 2005, which coincided with the increasing use of shrimp nets. Catch per unit effort for the shrimp net was lower in winter than summer. This study suggested that the population of Japanese eel in the river was probably small and unstable as indicated by the change of sex ratio and length distribution. In addition, the small-sized eel was more vulnerable to the shrimp net. The increase use of shrimp net might enhance the risk of growth overfishing. Thus, management and conservation by the control of fishing gear are necessary to sustain the eel population.

關鍵字

日本鰻 ； 族群結構 ； 性比 ； 體長組成 ； 漁具 ； 養殖鰻 ； 高屏溪 ； 台灣

並列摘要

To understand the effects of fishing gears and escaped cultured eels on the Japanese eel (Anguilla japonica) population in the Kao-Ping River, sex ratio and size composition of the eel caught by traditional eel tube and introduced shrimp net were investigated during the period from 1999 to 2006.Female eels were dominated in the catch before 2003 (＞70%) but significantly decreased to less than 60% in 2004 because of the cultured eels escaped from the pond. The median length and 95% length range of the eels caught by eel tubes was larger and narrower than that by shrimp nets, indicating that the selectivity differed between fishing gears. The percentage of eels less than 400 mm increased in the catch since 2005, which coincided with the increasing use of shrimp nets. Catch per unit effort for the shrimp net was lower in winter than summer. This study suggested that the population of Japanese eel in the river was probably small and unstable as indicated by the change of sex ratio and length distribution. In addition, the small-sized eel was more vulnerable to the shrimp net. The increase use of shrimp net might enhance the risk of growth overfishing. Thus, management and conservation by the control of fishing gear are necessary to sustain the eel population.

並列關鍵字

Anguilla japonica ； Population structure ； Sex ratio ； Length distribution ； Escaped cultured eel ； Gear selectivity