Zoological Studies

Comparison of Recapture Rates and Estimates of Fishing and Natural Mortality Rates of Japanese Eel Anguilla japonica between Different Origins and Marking Methods in a Mark-Recapture Experiment in the Kaoping River, Southern Taiwan

Yu-Jia Lin, Su-Lean Chang, Mei-Yu Chang, Shih-Huan Lin, Tzyy-Ing Chen, Mao-Sen Su, WeiCheng Su, and Wann-Nian Tzeng (2010) In total, 100 wild Japanese eels marked by microchips, 146 by pectoral fin clipping, and 100 cultured eels marked by microchips and 436 by caudal fin clipping were released in the lower reach of the Kaoping River, southern Taiwan. Recapture rates of marked wild eels did not significantly differ between individuals marked by microchips and pectoral fin clipping (p = 0.51), but did differ between cultured eels marked by microchips and caudal fin clipping (p = 0.01).  For wild and cultured eels marked by microchips, cultured eels had a significantly higher recapture rate than wild eels (p < 0.001), and eel length at release did not affect the recapture rates (p = 0.38).  According to the Akaike information criterion corrected for the sample size, estimates of fishing and natural mortality rates differed between pectoral fin clipping and microchips in wild eels.  However, neither rate differed between pectoral fin clipping and microchip in cultured eels.  Both eel origin and marking method might influence the recapture rate and mortality rate estimates.  Different behaviors of cultured eels in the wild and reaction to the marking process are possible reasons.  Higher mortality rates of wild eels marked by pectoral fin clipping were unexpected, probably due to a size-related mortality rate, behavioral changes, or mortality associated with pectoral fin clipping.