Estuary Specific Oyster Restoration Results

This content is excerpted from the GEMS Phase I Report: Oyster Reef Restoration.

Models have been specified for each technique in each estuary. General categories of services like wildlife for tourism or fish for recreational and commercial fishing are specified by identifying particular species that are more important for each service in each estuary (see below). In addition, estuary-specific external factors—biophysical (e.g., sedimentation) and social (e.g., harvest restrictions) factors that can change restoration outcomes—are specified (see below). The ESLMs also vary in which outcomes are relevant. For example, here is the general model compared to the complex structure, intertidal, NOT intensively harvested (living shoreline) technique in Galveston Bay, Texas:

ESLM Comparison Table

(See full size image)

The ESLM for a complex structure, intertidal, not intensively harvested oyster restoration (living shoreline) project in Galveston Bay, Texas, is layered on top of the general ESLM. White boxes with light blue, green, or yellow borders are outcomes or associated indicators in the general ESLM but are not dominant outcomes for this technique in Galveston Bay. The table at the right is an alternate way to show which outcomes are dominant for complex intertidal oyster reef restoration in Galveston Bay (checks indicate dominant outcomes). Tables similar to this one, showing dominant outcomes for different restoration techniques and estuaries, are included below without the accompanying ESLMs, but the outcomes included are drawn from ESLMs.

*Figure note: The adjacent habitat outcomes were not included in the dominant outcomes assessment, but often came up in discussion because many intertidal oyster reef restoration projects are done for the purpose of benefiting adjacent habitats. Therefore, these outcomes are included in the lists of dominant ecological outcomes for relevant focal estuaries.

The tables below show the dominant outcomes for each oyster restoration technique used at each focal estuary. 

Technique 1: Simple subtidal intensively harvested projects

Technique 2: Complex subtidal intensively harvested projects

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*Note on Technique 4 table: The adjacent habitat outcomes were not included in the dominant outcomes assessment, but often came up in discussion because many intertidal oyster reef restoration projects are done for the purpose of benefiting adjacent habitats. Therefore, these outcomes are included in the lists of dominant ecological outcomes for relevant focal estuaries.

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Wildlife species: Several outcomes of oyster reef restoration, such as recreational fishing, depend on individual wildlife species, and the most important species for particular outcomes vary across the Gulf of Mexico. Participants at the local workshops prioritized the top three species for each outcome:

Outcome Charlotte Harbor Back Bay of Biloxi Mobile Bay Chandeleur & Breton Sounds Galveston Bay
Harvest – Commercial Blue crab, mullet, shrimp Blue crab, brown shrimp, white shrimp Blue crab, brown shrimp, mullet Menhaden, blue crab, white shrimp Shrimp, blue crab, stone crab
Harvest – Recreational Snook, Tarpon, Red drum Speckled sea trout, blue crab, red drum Speckled trout, red drum, flounder Red drum, speckled sea trout, blue crab Spotted sea trout, flounder, red drum
Harvest – Subsistence Mangrove snapper, sheepshead, mullet potted sea trout, blue crab, sheepshead Blue crab, white trout, mullet Blue crab, red drum, croaker/speckled seatrout (tie) Croaker, blue crab, trout
Wildlife viewing
Wildlife viewing Dolphin, roseate spoonbill, white pelican/ manatee (tie) American oyster catcher, alligator, osprey Dolphin, alligator, blue heron/ brown pelican/ bald eagle/osprey (tie) Dolphin, alligator, bald eagle/other wading birds (tie) Brown pelican, great blue heron, American oystercatcher/great white egret/plover (tie)
Threatened & endangered American oystercatcher, smalltooth sawfish* Gulf sturgeon, West Indian manatee, oyster Gulf sturgeon, bald eagle, West Indian manatee Sea turtles, pelicans, Gulf sturgeon American oystercatcher, bottlenose dolphin, green sea turtle/loggerhead turtle (tie)

*Table note: This list of species is from discussions at the Charlotte Harbor local workshop, not from the formal prioritization process used for the other species lists in this table.

External drivers & factors: Local workshop participants identified external drivers—processes, events or policies that can change restoration outcomes. These drivers are outside the control of the project.

  • Climate and climate change
  • Extreme weather events
  • Oil spills and other disasters
  • Boat/barge activity
  • Land use
  • Water management, including freshwater releases and diversions
  • Freshwater inflows
  • Sediment diversions
  • Navigational dredging activity
  • Harvest policy and compliance, including harvest closures, overharvesting, and poaching activity (see below for details)
  • Restoration policy, including permitting requirements and funding constraints (see below for details)

Considering these drivers, participants identified and then prioritized the mechanisms through which each of these drivers influence the outcomes of oyster restoration projects in the focal estuary. First, we discussed the biophysical mechanisms (which we call external biophysical factors):

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Factors marked with a check received at least one vote during the prioritization exercise. Factors marked with two checks were among the top three identified as influential to oyster restoration project success during the priotization exercise. Factors with no checks are not necessarily unimportant; participants often noted that factors interact with each other and are difficult to consider individually.

Participants also identified the social, behavioral, and economic mechanisms that were important in each estuary. These mechanisms can determine the type and extent of oyster restoration projects in a certain area, where these projects are located, access, and what outcomes the projects will have.

  • Permitting requirements increase the cost of project implementation and can constrain project location (e.g. avoiding sensitive habitats or navigational channels)
  • There is often institutional resistance to placing restoration projects in non-harvestable areas, either due to health concerns (if areas are closed to harvest due to water quality issues) or because of public pressure to increase the number of oysters available for harvest.
  • Funding constraints can also influence the type and location of projects. For example, funding from the Louisiana state oyster program can only be used to create harvestable reefs.
  • Overharvesting can limit restored reefs’ long-term success and sustainability; the intensity of harvesting is partly determined by natural resource management policies, but poaching and theft are also common in some areas.
  • The availability and cost of materials (especially natural oyster shell cultch) influences which materials are used in restoration projects.