5C.3 Combining telemetry and mark-recapture methods to study the population dynamics of American Eels in Delaware

Friday, 13 November 2009: 2:00 PM
Marissa G. Brady, Delaware State University, Dover, DE; and P. B. Conn, L. L. Bailey, K. W. Shertzer, and D. A. Fox

In light of perceived declines in American eel populations, the ASMFC cited a need for tagging programs to address survival, mortality, and habitat use. Beginning in the spring of 2009 a combined mark-recapture and biotelemetry study was initiated in the St. Jones River, Delaware. Monthly mark recapture sampling events were initiated using previously selected locations (N = 40) in the St. Jones River, DE. The river was then broken into strata's based on commercial fishing practices (sites 1-14 (intense harvest), 15-25 (occasional harvest) and 26-40 (no harvest)). Beginning in June, American eels (N = 36) were implanted with an acoustic transmitter (V9-2L) and released at site of capture. To reduce biases we assigned one tag per sampling location. A combination of active and passive tracking was conducted; an array of seven passive receivers (VEMCO Ltd., VR2) were deployed in to maximize the probability of detecting American eels moving between strata's and migrating out of the system. Utilizing these methodologies we are assessing home range, habitat use and seasonal migration patterns in telemetered American eel. Through July 2009, we have collected a total of 33,734 detections of telemetered American eels and have successfully relocated the vast majority (33/36) of our telemetered individuals. Overall, we recorded more detections of tagged American eels in the middle/upper portions of the St. Jones river which correspond to regions that experience little, if any, harvest pressure. Additionally, we have documented acoustically tagged American eels moving between strata; although there is a strong tendency for individuals to home back to the site of initial tagging. The results from this project will aid managers in considering the design of future American eel management regimes including special management zones as they struggle to sustain this ecologically and economically important resources.
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