Abundance of Yellow-Phase American Eels in the Hudson River Estuary

Abstract

Fisheries for American eel Anguilla rostrata occur mostly in estuaries, yet eel abundance in large estuaries is poorly understood and the methods for estimating eel density underdeveloped. During 1997–1999, mark–recapture experiments were conducted for six consecutive days at six sites spanning the 250-km tidal portion of the Hudson River estuary, New York. Each experiment comprised 36 baited eel traps arrayed at 200-m intervals over 144-ha sampling sites. Estimates of local density were complicated by eel behavior, including trap-shy responses to marking and immigration into the experimental grid in response to bait attraction. We compared two open-population models, both modified Peterson methods: Jolly–Seber and a model created to account for eel behavior termed the mean recapture model (MRM). The biases in model outputs in response to trap-shy behavior and immigration were analyzed through simulations; the MRM showed less bias (−13%) than the Jolly–Seber model (+36%). Density estimates for the sampled regions ranged from 2 to 18 eels/ha for MRM and from 3 to 24 eels/ha for the Jolly–Seber model. The lowest density (1.6 eels/ha) was estimated for Albany (river km 240), but all other sites were estimated to have similar densities (5–18 eels/ha). The mean local density in the Hudson River estuary, 9.5 eels/ha, was much lower than those estimated for other systems. An overall abundance of 118,000 was calculated for Hudson River estuary eels larger than 30 cm (total length) at depths of 2–10 m.