Members of Langhei Ecology have a variety of experience conducting population modeling projects and stock assessments. Our experience includes studies for single and multiple stressors such as turbine passage, entrainment and impingement at cooling water intakes, altered flow regime, habitat loss, commercial and recreational harvest, sediment toxicity, and water quality.

Entrainment Modeling on the Lower Delaware River

As part of a compliance review conducted by Versar for the Delaware Department of Natural Resources, population modeling was performed to examine the effects of entrainment at a steam-electric power plant and a refinery located on the lower Delaware River. The empirical transport model (ETM; Boreman et al. 1978, 1981) was used to estimate the fractional losses of the early life stages of striped bass (Morone saxatilis) and weakfish (Cynoscion regalis), and of all life stages of bay anchovy (Anchoa mitchilli). Inputs to the model included early life history characteristics (e.g. ontogeny) and spatial distribution of the fishes in the estuary, as well as location and magnitude of water withdrawals and through-plant mortality.

Effects of Toxic Sediments on a Frog Population

In support of an ecological risk assessment at a contaminated industrial site in Massachusetts, Langhei Ecology developed a population model for the green frog (Rana clamitans melanota). The model was used to project population-level effects from laboratory-derived toxicity data. Sediment toxicity data provided to Langhei Ecology were obtained using the FETAX (Frog Embryo Teratogenesis Assay - Xenopus) protocol and sediment samples from several locations at the site. Density-dependent survival of larvae, which has been documented in several species of Ranid frogs, has the potential to mitigate population-level effects of toxicity. The model yielded frog abundance as a function of sediment toxicity and alternative assumptions about the nature of density-dependent survival.

Modeling of Atlantic Salmon Restoration in the Penobscot River Basin

The likelihood of successful restoration of the Penobscot River stock of Atlantic salmon (Salmo salar) was examined using two modeling approaches. The ASAL model (Rago and Goodyear 1985) was used to project run sizes and nursery habitat utilization, and associated probabilities, under various dam construction, removal, and mitigation scenarios. ASAL is a comprehensive, stochastic, life history model that takes into account the spatial configuration of nursery habitat and sources of mortality for migrating salmon in a river basin and at sea. Deterministic, spreadsheet models were also constructed and used to compare the effects of various mitigation measures on potential run size, number and fraction of returning adults that reach their spawning grounds, and the number and fraction of smolts that reach the sea. This work was part of an Environmental Impact Statement prepared under Versar's FERC support subcontract with Stone and Webster Environmental Services.

This project is also described under the following categories:
Watershed- and Regional Scale Ecological Risk Assessment
Hydropower and Fisheries

Risk of Establishing a Feral Population of Grass Carp in the Potomac River

A stochastic population model for grass carp (Ctenopharyngodon idella) was developed and applied to the Potomac River basin to examine the risk to submersed aquatic vegetation (SAV) in the river from this non-native fish which is stocked into impoundments within the drainage basin. The model included uncertainty in the process of inducing triploidy (i.e. functional sterility) and uncertainty in the effectiveness of screening efforts to ensure that only triploid fish are stocked. The model also included stocking rate, a stochastic escape rate, and demographic stochasticity to examine the potential for establishment of a feral population through stocking of nominally triploid fish. Grass carp numbers derived from the model were used to scale SAV consumption and examine the potential for adverse effects on SAV in the Potomac River estuary. This work was funded by the U.S. Environmental Protection Agency through contracts to Versar.

This project is also described under the following project category:
Watershed- and Regional-Scale Ecological Risk Assessment

Population Model for an Experimental Salmon Stocking Program

A stochastic population model was constructed and used to evaluate a proposed experimental stocking of Pacific salmon in a tributary of the Delaware River. The primary questions to be addressed by the modeling effort were the total number of salmon expected to return each year, and the density of strays in non-natal streams. The model incorporated life history characteristics of each of three species and probability distributions for return rates and stray rates derived from the literature. A key feature of the model was explicit simulation of the dispersion of returning salmon among non-natal streams (i.e. straying) to generate probability distributions of the maximum number of strays in any one stream. The three species examined were: steelhead (Oncorhynchus mykiss), coho salmon (Oncorhynchus kisutch), and chinook salmon (Oncorhynchus tshawytscha). The model tracked fish from the first of three annual stockings through return of the last fish. The project was undertaken as part of a Draft Environmental Impact Statement prepared by Versar for the U.S. Fish and Wildlife Service and the New Jersey Division of Fish, Game and Wildlife.

This project is also described under the following project category:
Watershed- and Regional-Scale Ecological Risk Assessment

Evaluation and Application of a Shad Population Model for the Susquehanna River

Under Versar's contract with the Maryland Department of Natural Resources Power Plant Research Program, support was provided for developing a settlement agreement on upstream fish passage facilities on the Susquehanna River. A licensee-sponsored population model for American shad (Alosa sapidissima) was reviewed, the model was modified, and additional runs were made to examine the need and construction schedule for upstream passage facilities on the River. The licensee-sponsored model included both biological parameters and reach-specific parameters for juvenile production and dam passage. The structure, behavior, and parameterization of the licensee's model was critically reviewed, modifications were made to the model to examine the importance of simplifying assumptions, and a sensitivity analysis was performed to test the robustness of the model predictions.

This project is also described under the following project categories:
Hydropower and Fisheries
Fish Behavior

Distribution and Abundance of Sandhill Cranes in Response to Habitat Changes on the Middle Platte River, Nebraska

Langhei Ecology provided analytical support for U.S. EPA's middle Platte River floodplain ecological risk assessment case study. As part of this project, Langhei Ecology developed a model of the distribution and abundance of sandhill cranes (Grus canadensis) in relation to habitat changes in the floodplain. The middle Platte River is an important stopover point for 80% of the continental sandhill crane population. Each spring sandhill cranes spend several weeks roosting in the active river channel and foraging in nearby wet meadows and crop land. Fat accumulated during this period sustains them during subsequent northward migration and nesting. The population model developed by Langhei Ecology is a tool for examining the risk that continued habitat loss poses to crane abundance and distribution, and the potential benefits of targeted habitat protection and restoration.

This project is also described under the following project category:
Watershed- and Regional-Scale Ecological Risk Assessment

Evaluation of Alternative Hypotheses for the Decline of Striped Bass in the Roanoke River

A stock assessment was conducted for striped bass (Morone saxatilis) in the Roanoke River, North Carolina. The Roanoke River stock experienced a marked decline during the 1970's and 1980's, as did stocks coast wide. Various stock assessment analyses were conducted to examine the hypothesis that commercial and recreational harvest were the cause of the decline. An alternative hypothesis, that the decline was primarily due to decreased recruitment success, was also examined. These analyses were conducted under a contract held by Versar to support the City of Virginia Beach.

This project is also described under the following project category:
Hydropower and Fisheries

Entrainment Impacts of a Proposed Expansion of a Power Plant on the Nanticoke River

Population modeling was conducted to assess potential entrainment impacts on striped bass in the Nanticoke River (Maryland). Two modeling approaches were used to evaluate potential impacts: the empirical transport model (Boreman et al. 1978, 1981) and a projection of the number of adults equivalent to the number of eggs and larvae entrained. The study examined two different wedgewire screen slot widths, three intake locations, and two pumping rates. The study also investigated the impact of existing operations and how upgrades required for the expansion could affect existing impacts. Uncertainties in the major inputs to the equivalent adults model were propagated through the analysis. These analyses were conducted under Versar's contract with the Maryland Department of Natural Resources Power Plant Research Program.

Evaluation of Potential Entrainment by a Municipal Water Treatment Facility on the Rappahannock River, Virginia.

Spotsylvania County, Virginia, is building a water treatment facility (Motts Run Water Treatment Plant) that will withdraw water from the Rappahannock River. During high flow events, water will also be withdrawn from the Rapidan River (a tributary upstream of the Motts Run intake), stored in an off-stream reservoir, and released during low-flow periods to offset withdrawals at Motts Run. Anadromous fishes, such as shad and river herring, are currently excluded from these reaches of the river by Embrey dam, which is located approximately 3.5 miles downstream of the Motts Run intake site The Commonwealth of Virginia plans to remove the blockage at Embrey dam and restore runs of shad and river herring to the Rappahannock River basin. Current permit conditions require 1mm slot width wedge-wire screens on the intakes to exclude eggs and larvae resulting from future spawning runs of shad and river herring. Spotsylvania County wishes to modify the permit conditions to allow 2mm screens. This project estimated potential entrainment of American shad (Alosa sapidissima), hickory shad (Alosa mediocris), alewife (Alosa pseudoharengus), and blueback herring (Alosa aestivalis) at the two intake sites under current permit conditions and under the revised permit conditions proposed by Spotsylvania County. The empirical transport model, was used to combine the limited information available for the Rappahannock River upstream of Embrey dam with life history information, information on the effectiveness of 1mm and 2mm screens as a function of egg and larval size, and intake characteristics to project entrainment of eggs and larvae.

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