The Development of a Non-Lethal Maturity Index for American Eels

In recent decades eel populations have declined across the globe, making them of increased research and conservation interest. The catadromous, semelparous and panmictic nature of eels make them difficult to study and manage. The sexually mature life stage (silver eel) is relatively understudied, yet the transition to a silver eel is critical for species perseverance. Previous research suggests eels need to reach a minimum fat content before maturity. The recent use of bioelectrical impedance analysis (BIA) in fisheries science to measure the composition and condition of fish, including fat content, may help in developing a non-lethal index of maturity in eels. BIA readings can be taken easily in the field without harming subject animals. A non-lethal index of silvering could be a powerful management tool for future research of catadromous eels. We collected BIA readings and morphometrics such as head length, eye diameter and fin length on eels caught in tributaries to the Hudson River to correlate with internal characteristics of maturity such as total lipid content and gonad, stomach and liver weight. We repeatedly surveyed one tributary and PIT tagged eels after taking measurements, then caught emigrating eels during the fall migration season to re-assess biometric characteristics.