Assessing Impacts of Navigation Dredging on Atlantic Sturgeon (Acipenser oxyrinchus).

摘要

The outcome of encounters between Atlantic sturgeon (Acipenser oxyrinchus) and active dredging operations in Federal navigation channels is dependent on a number of factors. Risk factors include: avoidance of or attraction to the presence of an active dredge, the proportion of time spent in bottom waters of the navigation channel along with other behavioral aspects of the target species. To assess potential entrainment by a CSD operating in the James River, Virginia, five Atlantic sturgeon (TL = 77.5-100 cm), were implanted with both active and passive transmitters, released in the immediate vicinity of the dredge, and tracked continuously for several days. During tracking the dredge intermittently pumped sediment through a pipeline to an open-water placement site. Movements were monitored using mobile vessel-based omni-directional hydrophones as well as data logging receivers placed at fixed up- and downstream locations. Data on lateral and vertical movements of individual sturgeon were examined in relation to river bathymetry, river discharge rate, dredge production rate, and vessel traffic. Continuous records of tag depths provided observations of the durations and frequencies of individual sturgeon excursions into channel basin waters. None of the tagged sturgeon showed evidence of avoidance behavior, remaining in close proximity to the dredge for as long as 21.5 hours before moving away. Likewise, no strong evidence of attraction was observed, as sturgeon moved within the channel past the operating dredge on several occasions. Movements tended to be influenced by tidal flows. Only one individual moved against the prevailing tidal flow. Three of five tagged sturgeon demonstrated similar diel movement patterns, spending approximately 95% of their time in the lower 1.5 m of the channel bottom. Two sturgeon showed a distinct pattern of moving into waters.