Benson Beach Demonstration Project: Composition and Abundance of Biota at Three Alternative Sump Sites

Williams, Greg D.; Pearson, Walter H.; Evans, Nathan R.; Anderson, M.

doi:10.2172/15010484

Cited by 5 publications

(11 citation statements)

References 6 publications

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“…In spring and summer, age 0+ crab can be found in the MCR and the estuary with annual average densities varying over two orders of magnitude from year to year (Larson 1993). In the fall of 2003, Williams et al (2004) observed an abrupt increase of the density of age 1+ crab in shallow subtidal areas south of the north jetty in the MCR.…”

Section: Synopsis Of Dungeness Crab Biologymentioning

confidence: 97%

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Dungeness Crab Dredging Entrainment Studies in the Lower Columbia River, 2002 ? 2004: Loss Projections, Salinity Model, and Scenario Analysis

Pearson¹,

Williams²,

Skalski³

2005

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Dungeness crab studies conducted in 2002 for the Portland District of the U.S. Army Corps of Engineers (Corps) constituted a major step forward in quantifying crab entrainment through statistical projections of adult equivalent loss (AEL) and loss to the fishery (LF) from proposed construction and maintenance dredging in the Columbia River navigation channel (Pearson et al. 2002, 2003). These studies also examined the influence of bottom salinity on crab abundance and entrainment rates. Additional sampling was conducted in 2004 to improve loss projections, further develop the crab salinity model, and apply the model to assess correlations of entrainment rates and projected losses with seasonal salinity changes. Measurements of crab-entrainment rates were made aboard the Corps Dredge, Essayons, during August and September 2004 at Flavel Bar, Desdemona Shoals, and the mouth of the Columbia River (MCR). In both 2002 and 2004, rates decreased from the MCR to upriver locations. An appreciable increase, however, was observed in entrainment of age 0+ crab, populations of which are known to vary among years and episodically within a year. In 2004, entrainment rates at Flavel Bar were similar to those at Upper Sands, which also has similar salinity regimes. Desdemona Shoals, on the other hand, had bottom salinities intermediate between those of the MCR and the upriver locations and also had the most variable entrainment rates. The MCR, dominated by oceanic water with bottom salinities above 28 psu for 98% of the summer observations, had consistent entrainment rates (0.05 to 0.10 crab/cubic yard). A statistical procedure for ratio estimation was used to hindcast the 2002 entrainment rates for Flavel Bar from the 2002 and 2004 data, and a modified Dredge Impact Model (DIM) was used to project crab AEL and LF for the dredged volumes proposed for the Channel Improvement Project. The results improved the previous estimates of loss in two ways: first, the estimates were based on site-specific data, and second, the additional 2004 data reduced the variance and narrowed confidence limits. No crab population estimates are available against which to judge the AEL at ages 2+ and 3+, although the commercial crab landings from the regions adjacent to the Columbia River enable a comparison based on the LF values. Regression analysis with the 2002 and 2004 data was used to develop the salinity model for crab occurring in the MCR and navigation channel. The model showed that the natural logarithms of entrainment rates for ages 2+ and 3+ crab are significantly related to salinity. As the salinity decreases from oceanic values, the entrainment rates for this age group decrease exponentially. In areas where salinity observations are lower than 16 psu at least 50% of the time (e.g., near the Astoria Bridge in summer), the model predicts that entrainment rates will be a fraction (less than 6%) of those where salinity remains below 16 psu only 2% of the time (e.g., the MCR in summer). According to results, the entrainment of younger crab are g...

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Section: Synopsis Of Dungeness Crab Biologymentioning

confidence: 97%

“…Researchers conducted crab-entrainment studies aboard the Corps dredge, Essayons, in 2004, using the methods described in previous reports (Pearson et al , 2004. A brief overview of these methods, with a description of relevant modifications, is provided below.…”

Section: Field Sampling Effortmentioning

confidence: 99%

Dungeness Crab Dredging Entrainment Studies in the Lower Columbia River, 2002 ? 2004: Loss Projections, Salinity Model, and Scenario Analysis

Pearson¹,

Williams²,

Skalski³

2005

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“…The proposal for the SWLDR uses a cutter suction (pipeline) dredge to pump up to 500,000 cy of material from the proposed sump area to Benson Beach over approximately 6 weeks in summer, planned for July 15 through August 31. The proposed sump area ( Figure 1) is 600 ft by 3000 ft, or 16.7 hectares (ha); its location was selected as being less impacting to the North jetty and is expected to have a lower abundance of crab during the proposed dredging season than would other previously proposed sump areas located slightly to the east, based on trawl surveys conducted in the summer of 2003 (Williams et al 2004). The total project volume was assumed to be 500,000 cy for the purpose of estimating crab entrainment in the DIM.…”

Section: Dredging Scenariosmentioning

confidence: 99%

“…However, there are no existing data for the exact location of the candidate sump area. Existing data are available for nearby previously proposed sump areas (Williams et al 2004), for the Columbia River Bar and estuary (Emmett and Durkin 1985;McCabe et al 1986;McCabe and McConnell 1989;and Larson 1993), and for other coastal estuaries (Rooper et al 2002). Density estimates, age distribution and sex ratios, and gear efficiency uncertainty for the existing data were considered when selecting the SWLDR DIM input data and assumptions.…”

Section: Crab Population Densitymentioning

confidence: 99%

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Impacts to Dungeness Crab from the Southwest Washington Littoral Drift Restoration Project

Williams¹,

Kohn²,

Pearson³

et al. 2005

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Preliminary Assessment of Potential Impacts to Dungeness Crabs from Disposal of Dredged Materials from the Columbia River

Pearson¹,

Miller²,

Williams³

et al. 2006

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Dredging of the Columbia River navigation channel has raised concerns about dredging-related impacts on Dungeness crabs (Cancer magister). The overall objectives of this effort are to synthesize what is known about disposal effects on Dungeness crabs (Phase 1) and to offer approaches to quantify the effects, including approaches to gain a population-level perspective on any effects found in subsequent studies (Phase 2). This report documents Phase 1, which included 1) development of a conceptual model to integrate knowledge about crab biology and the physical processes occurring during disposal, 2) application of physics-based numerical modeling of the disposal event to understand the physical forces and processes to which a crab might be exposed during disposal, 3) conduct of a vulnerability analysis to identify the potential mechanisms by which crabs may be injured, and 4) recommendations of topics and approaches for future studies to assess the potential population-level effects of disposal on Dungeness crabs. The conceptual model first recognizes that disposal of dredged materials is a physically dynamic process with three aspects: 1) convective descent and bottom encounter, 2) dynamic collapse and spreading, and 3) mounding. Numerical modeling was used to assess the magnitude of the potentially relevant forces and extent of mounding in single disposal events. The modeling outcomes show that predicted impact pressure, shear stress, and mound depth are greatly reduced by discharge in deep water and somewhat reduced at longer discharge duration. The analysis of numerical modeling results and vulnerabilities indicate that the vulnerability of crabs to compression forces under any of the disposal scenarios is low. Modeling results and other information suggest that crabs may be vulnerable to injury from surge currents under some but not all disposal scenarios. For the shallow-water, short-duration disposal scenarios, the shear stress and surge currents estimated from the modeling and observed in the field at Palos Verdes appear to be sufficiently high to mobilize and transport bottom sediment and at least juvenile crabs. The surge currents estimated from modeling the deep water scenarios are not sufficient to mobilize sediment greater than 1 mm or juvenile crabs. The effects of such movement, if any, are not known and can be reduced by behavioral responses by crabs. There is evidence that burial by dredged materials can affect crab respiration and survival, but confounding factors in previous experiments preclude conclusions about thresholds and extent of effects. We recommend that future studies focus on burial effects during shallow water, short duration disposal scenarios and take into account the potential for behavioral responses to mitigate any effects.iii During disposal, the characteristics of the dredged materials (e.g., size distribution, cohesiveness), the water column (e.g., depth, stratification, currents), and the bottom (e.g., slope, grain-size distribution) interact to determine the characteristic...

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Benson Beach Demonstration Project: Composition and Abundance of Biota at Three Alternative Sump Sites

Cited by 5 publications

References 6 publications

Dungeness Crab Dredging Entrainment Studies in the Lower Columbia River, 2002 ? 2004: Loss Projections, Salinity Model, and Scenario Analysis

Dungeness Crab Dredging Entrainment Studies in the Lower Columbia River, 2002 ? 2004: Loss Projections, Salinity Model, and Scenario Analysis

Impacts to Dungeness Crab from the Southwest Washington Littoral Drift Restoration Project

Preliminary Assessment of Potential Impacts to Dungeness Crabs from Disposal of Dredged Materials from the Columbia River

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