Stories From The Field

Characterizing Fish Habitat within the Northern Gulf of Mexico Coastal Waters

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Issue

Commercial and recreational fisheries within Galveston Bay and the northern Gulf of Mexico contribute significantly to the region’s ocean economy, making effective management a priority. Historically, fisheries management has been based on assessments of the fisheries stock that drive regulatory decisions such as allowable catch limits, size ranges, open seasons, and area closures. More recently, managers have recognized the need to manage living marine resources in a more holistic approach, including sound management of the species’ habitat. To explore the benefits of this approach, a case study was proposed to study brown shrimp habitat in Galveston Bay. The study would employ the Federal Geographic Data Committee’s newly approved Coastal and Marine Ecological Classification Standard (CMECS), which provides a consistent framework and common terminology for describing natural and human-influenced coastal and marine ecosystems. Because CMECS is applicable from the upper tidal reaches of estuaries to the deepest portions of the ocean, it allows a more complete assessment of habitat across state and federal boundaries. In addition, the case study’s use of high-temporal-resolution satellite oceanographic data would further improve the ability to manage resource habitats on a large, regional scale.

Process

High-Resolution MODIS (Moderate Resolution Imaging Spectroradiometer) satellite data for sea surface temperature and chlorophyll, as well as modeled salinity, photic depth, and bottom-to-surface temperature differences, collected between 2005 and 2009, were evaluated for their utility in identifying optimal habitat for commercially managed living marine resources. _In situ_ fisheries data from the Southeast Area Monitoring and Assessment Program (SEAMAP) were overlaid on the satellite-derived data in ArcMap to validate the satellite data. Raw data from both sources were reclassified into CMECS categories. The SEAMAP and satellite-derived products for Galveston Bay revealed areas of favorable water conditions for brown shrimp as post-larvae move into the estuary. Since substrate and the availability of intertidal vegetation are other key factors in this process, sediment grab sample data (U.S. Geological Survey’s usSEABED database) and emergent wetland vegetation data (National Wetlands Inventory) were overlaid on the raster map of favorable water conditions. Within Galveston Bay, over 400 samples fell into the sand or sandy mud categories favored by brown shrimp. Most of the other samples in the area showed other unconsolidated bottom classes that, although not optimal, indicated that the great majority of Galveston Bay was at least acceptable substrate for the shrimp. The National Wetlands Inventory data showed extensive salt marsh in the bay, although much of it did not coincide with favorable water conditions.

Impact

The Galveston case study suggests that including a variety of environmental information (water column, substrate, etc.) for key life stages of the brown shrimp has the potential to add valuable information to the current essential fish habitat maps and could aid with the decision-making process. Also, the addition of other parameters, such as bathymetry and sediment data, both of which can be acquired through NOAA’s Digital Coast, would allow resource managers to use the products to identify the best areas for restoration or protection. Maps demonstrating how these data might be useful to resource managers in the decision-making process were presented to stakeholders and were seen as useful for improved restoration planning and fisheries management.

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Favorable sediment and wetlands for post-larval shrimp
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