Salt marsh construction costs and shrimp production in Galveston Bay and Gulf of Mexico from 1999-01-01 to 2005-01-01 (NCEI Accession 0161218)

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Contact by email preferred.

Gulf Of Mexico

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Cite this article as: Roth BM, Rose KA, Rozas LP, Minello TJ (2008) Relative influence of habitat fragmentation and inundation on brown shrimp Farfantepenaeus aztecus production in northern Gulf of Mexico salt marshes. Mar Ecol Prog Ser 359:185-202. https://doi.org/10.3354/meps07380

After sample collection, field data were entered into an Excel spreadsheet or database file (DBF) using database manager software. A text file was created to describe these data and associated variables. Entered data were checked against the field sheets by two biologists to minimize entry errors. Samples were processed in the laboratory, sorted, specimens identified and measured, and information was entered into an Excel spreadsheet or DBF file. Files were printed out and compared against original data sheets by two biologists for data entry errors. Corrections were made at this time, the electronic file was saved, and a back-up copy made. Hard copies of the QCd files were printed and stored in the project folder along with the original field and laboratory data sheets. The electronic file was also sorted and examined by the Lab Supervisor or other project personnel in a variety of ways to look for outliers, missing data, and other potential errors. Verified data files were then saved electronically on the Galveston Laboratory server and backed-up as needed.

How were the catch and price data obtained ?

Catch and price data were provided by the Texas Parks and Wildlife Department for whole shrimp (corrected from heads off values when appropriate) landed from West Bay, where most of the marsh restoration projects were located in the Galveston Bay system. In 2007, the catch composition included shrimp for bait (11.6% live bait and 5.5% dead bait; brown shrimp and white shrimp combined) and for human consumption (1.5% white shrimp and 81.4% brown shrimp). Of these categories, the ex-vessel price of live bait was highest at U.S. $8.07 kg-1 ($3.66 lb-1), and the overall weighted-average price of the landings was $4.72 kg-1. This latter price was used to estimate the value of the exported shrimp biomass from the constructed marshes.

How were construction costs determined ?

We obtained construction costs from project managers, resource agencies, and local sponsors. These costs were categorized into 1) engineering design; 2) equipment mobilization and demobilization; 3) construction of wetland platforms (e.g., terraces or mounds); 4) construction of breakwaters to prevent erosion; and 5) planting of marsh vegetation. To facilitate the comparison of projects, we tried to include only items 1–3 in our estimates of construction costs. Costs of engineering design were included when available, but some projects benefited from previously developed engineering specifications. We did not include the cost of building breakwaters or wave barriers to protect the sites. The necessity for constructing such barriers is site specific and was limited to three projects (GISP Terraces, Jumbile Cove I, and Delehide Cove). Including these large costs (which could be avoided by selecting an alternate site) would unduly bias the overall estimates. We also did not include the cost of planting vegetation, because most projects employed volunteers and did not have to bear these costs. All costs were adjusted for inflation and standardized to 2007 U.S. dollars based on a Composite Cost Index developed by the U.S Army Corps of Engineers for Civil Works construction projects (USACOE 2009).

How were Population size and annual production for brown shrimp and white shrimp were estimated ?

Population size and annual production for brown shrimp and white shrimp were estimated following the methods described in Minello et al. (2008). Bands of vegetation and water at different distances from the marsh edge were constructed with the GIS. Our modeling approach then assigns shrimp densities to these bands based on observed density patterns across the natural marsh surface in Galveston Bay. These densities peak in the vegetated marsh edge at 13.4 brown shrimp m-2 and 8.9 white shrimp m-2 and decline both into the vegetation and out into open water. Shrimp population estimates for a project area are derived from these density patterns combined with information on the proportion of the project area at different distances from the marsh edge. Marshes that maximize the amount of marsh edge ecotone generally have the highest population values. Production is then estimated using an equilibrium yield approach that assumes stable size frequency distributions (estimated from a large database of shrimp collected in the bay) and constant daily growth rates of 1 mm total length (Minello et al. 2008). The applicability of our models to constructed wetlands is supported by the similarities in shrimp density patterns and growth rates between the GISP terrace marsh and a natural reference marsh.

How were project areas defined ?

Defining a project area, and therefore the size of a project, is important in obtaining funding and assessing project success and performance. The projects we analyzed were designed to incorporate marsh edge, based partly on studies showing elevated nekton densities both in the vegetation and open water adjacent to this edge. Therefore, proposed project areas should include both emergent vegetation and shallow water. Because the outer project boundaries affect area and construction cost calculations, we standardized the designation of these boundaries and defined the project area using a 25-m buffer around marsh vegetation (Fig. 2). Small amounts of water greater than 25 m from marsh that were within these outer boundaries (less than 2.4% of any project area) were included in the project area. We also provided calculations of construction costs in relation to strictly the area of emergent marsh.

How was natural predation treated in the model ?

This modeling approach provides estimates of total annual shrimp production from wetland habitats that include the production lost to natural mortality. Roth et al. (2008) used an individual based model to examine effects of marsh landscape configuration and tidal inundation on brown shrimp production from wetlands, and they estimated that 37.5% of total production was lost to predation.

Based on these results, we estimated that 62.5% of shrimp total biomass production would be exported to the bay and be available to fishers.

What references were used in reference to the frequently asked questions ?

Minello TJ, Matthews GA, Caldwell P, Rozas LP (2008) Population

and production estimates for decapod crustaceans in wetlands of

Galveston Bay, Texas. Transactions of the American Fisheries

Society 137:129–146

Roth BM, Rose KA, Rozas LP, Minello TJ (2008) Relative influence

of habitat fragmentation and inundation on brown shrimp

Farfantepenaeus aztecus production in northern Gulf of Mexico

salt marshes. Marine Ecology Progress Series 359:185–202

USACOE (2009) United States Army Corps of Engineers, Civil

Works Construction Cost Index System (CWCCIS), Appendix

revised 31 March 2009. CECWE-EE Manual No 1110–2–1304.

How were patterns of vegetated land and water for assessed for each marsh ?

We assessed the patterns of vegetated land and water for each marsh through a Geographic Information System

(GIS) analysis based on digital color orthophotography at 1/4800 scale taken in 2006 by Kucera International Inc. for

the Houston-Galveston Area Council (available at http://www.h-gac.com/rds/). GIS models of each marsh system

were developed by onscreen digitization of the edge of the marsh vegetation using ArcGIS 9.2, the Spatial Analyst extension, and the Editor Tool Bar (ESRI, Redlands, CA). There was not a lot of spectral confusion in these images, and marsh vegetation was usually distinct from nonvegetated areas. No formal ground truthing was conducted, but sites were visited and local experts consulted to ensure that no major classification errors occurred. We consider the final GIS images to be models, because several subjective decisions were needed to make equivalent comparisons among the different constructed marshes. In situations

where emergent marsh areas had not been completely vegetated, we assumed that these areas would fill in with time and classified the areas as marsh. In addition, some of the constructed wetlands were located near natural marsh or breakwaters, and we used the GIS software to substitute shallow water for such areas adjacent to constructed marsh. This approach allowed us to compare projects as if they were all constructed in open shallow water and prevented adjacent habitats from affecting the modeled estimates of shrimp production. Without this substitution, for example, the natural marsh adjacent to the Delehide Cove project would have been incorporated into the buffer surrounding this constructed marsh and likely increased our shrimp production estimates for the project.