Combining mark-recapture and telemetry to understand American eel population dynamics

Recently fishery managers have begun to combine mark-recapture and telemetry modeling approaches to provide estimates of survival, mortality and emigration.  In the spring of 2009, a combined mark-recapture and telemetry study was initiated in the St. Jones River, Delaware.  Monthly mark-recapture events took place using fixed locations (n = 40) stratified by commercial fishing practices (i.e. intense, occasional, and no harvest). One American eel (>400 mm) at each sampling location was implanted with an acoustic transmitter, released, and monitored through both active and passive telemetry.  The vast majority (38/40) of telemetered individuals were detected during the study.  During the summer months, site fidelity was very high for the majority (24) of detected eels which remained at the site of initial tagging.  In the late fall 16 detected American eels moved to higher saline waters of the Delaware Bay possibly for thermal refugia. This project is relatively unique as we have developed a formalized partnership with commercial harvesters, to build a better understanding of the impact of harvest on American eel behavior.  We are currently developing multi-state models to provide estimates of emigration, survival, and seasonal habitat use for American eels.