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原文传递 Impacts to Dungeness Crab from the Southwest Washington Littoral Drift Restoration Project.

题名：	Impacts to Dungeness Crab from the Southwest Washington Littoral Drift Restoration Project.
作者：	williams, g. d. kohn, n. p. pearson, w. h. skalski, j. r.
关键词：	pipelines, population density, pumping, sand, shores
摘要：	The Southwest Washington littoral drift restoration project is a demonstration project that will restore sand to the littoral cell in southwest Washington. This preliminary restoration demonstration project is part of the U.S. Army Corps of Engineers (Corps) Southwest Washington Littoral Drift Restoration Regional Sediment Management program. The planned demonstration project will place sand on Benson Beach, the public beach north of the North Jetty at the mouth of the Columbia River (MCR), and then move the sand into the offshore littoral zone. One proposal for doing this involves pumping the material from a sump area that would be created on the south side of the jetty to Benson Beach using a cutter suction dredge, also known as a pipeline dredge. If this one-time demonstration project proves feasible and successful, up to a million cubic yards of sediment could be used to replenish the outer coast littoral drift system in successive years by the same process. The primary goal of this study was to assess the potential risk of impacts to Dungeness crab from the proposed demonstration process of using the cutter suction dredge to move sediment from the proposed sump area on one side of the North Jetty to the beach on the other side of the jetty. Because there are no direct measurements of crab entrainment by pipeline dredge operating outside of the lower Columbia River navigation channel, dredge impacts for the proposed demonstration project were estimated using a modification of the dredge impact model (DIM) of Armstrong et al. (1987). The model estimates adult equivalent loss (AEL) of crab using crab population density from trawl surveys, dredge project information (gear type, season, location, volume), and an entrainment function relating crab population density to entrainment by the dredge. The input used in applying the DIM to the Southwest Washington littoral drift restoration demonstration included the specific dredging scenario provided by the Corps, existing data on crab density in previously proposed sump areas, and a series of entrainment functions. A total of fourteen scenarios were modeled and the outcomes compared with six reference scenarios intended to represent realistic to worst cases. Dungeness crab entrainment and subsequent loss of recruitment to adult age classes and the crab fishery estimated for the Southwest Washington littoral drift restoration project varied widely (over three orders of magnitude) because of the range of assumptions about initial crab density, dredging scenarios, and entrainment functions. Estimated AEL of crab recruited to age 3 years and up ranged from 57 to 9,373 crab; estimated loss of crab recruited to the fishery (males only) ranged from 20 to 3281 crab. Reference scenario results demonstrated that losses to the fishery are probably less than 2000 crab and more likely less than 1500 crab. Although the comparison to reference scenarios helps put the results in perspective, losses to the crab fishery could still span two orders of magnitude. This uncertainty can only be assessed by direct measurements of crab entrainment during the demonstration project, which is recommended to more accurately evaluate crab losses, not only from the single demonstration event but from cumulative losses from successive restoration efforts.
总页数：	u0708；49p
报告类型：	科技报告