TEXAS GEMS - Shamrock Island Management Complex

Site Description

Shamrock Island and the adjacent Francine Cohn Preserve are owned and managed as a single unit by The Nature Conservancy. Shamrock Island is the remainder of a re-curved barrier spit that once extended southwestward from Mustang Island into Corpus Christi Bay. Shamrock Island was formed when Hurricane Celia breached this re-curved barrier spit in 1970. Since its formation Shamrock Island has become one of the most important colonial waterbird rookery islands in the Northwestern Gulf of Mexico. The Francine Cohn Preserve located just south of Shamrock Island on the backside of Mustang Island is a system containing inter-tidal marsh, subtidal seagrass meadows, high marsh, open water, shell beaches, freshwater ponds, and wind tidal flats. An important biological connection exists between Shamrock Island and the Francine Cohn Preserve, as birds nesting on the island rookery are known to forage in the marsh habitats found on the western side of Mustang Island.

Date Site Established:

Shamrock Island was purchased in 1995. The Francine Cohn Preserve was acquired in April 2000 following a generous donation by Mr. Marcus Cohn of 22 acres followed by the purchase of an adjoining 278 acres from a private landowner with the vital assistance of the Coastal Bend Bays and Estuaries Program, and Citgo. Since April 2000 Shamrock Island and The Francine Cohn Preserve has been managed as a single complex.

Date When Information Last Updated:

2003-06-22

Location:

Nueces County, State of Texas
Shamrock Island: UTM Zone 14 Northing 3,071,803.02 Easting 680,281.18
Francine Cohn Preserve: UTM Zone 14 Northing 3,068,286.38 Easting 680,927.69

Relative Size:

Total = 374 acres (Shamrock Island 74 acres, Francine Cohn Preserve 300 acres)

Area of Influence:

Mustang Island, Nueces County, Corpus Christi Bay

Ecological and Cultural Characteristics

Habitat Type:

Shamrock Island was a re-curved barrier island spit located on the back of Mustang Island, Nueces County, Texas. The islands habitats include: sand/shell beach, grass/shrub xeric upland, wetland (low, mid and high marsh), and small lagoon areas. The Francine Cohn Preserve located just south of Shamrock Island on the backside of Mustang Island is a system containing inter-tidal marsh, subtidal seagrass meadows, high marsh, open water, shell beaches, freshwater ponds, and wind tidal flats.

Rare/Endangered Species:

Piping plovers, peregrine falcons, reddish egrets, tricolored herons, great blue herons, ibises, and roseate spoonbills.

Breeding/Feeding/Nursery Area:

Since the breaking of the land bridge, Shamrock Island has become one of the most important colonial bird nesting islands on the Texas coast. Up to 21 bird species, including the threatened reddish egret and white-faced ibis, nest on the island. The island includes high quality beach habitat used by four species of terns (gull-billed, Sandwich, Caspian and royal). In some years, royal terns number close to 8,000 on Shamrock Island, making it by far the most important nesting site for this species on the Texas coast. Black skimmers also use the shell beach sites. More vegetated shell hash flats provide nesting habitat for up to 6,000 laughing gulls. On the beach ridges vegetated by salt cedar, nesting species include great blue herons, little blue herons, tricolored herons, black-crowned night herons, great egrets, snowy egrets, reddish egrets, white-faced ibis and roseate spoonbills. An important biological connection exists between Shamrock Island and the Francine Cohn Preserve, as birds nesting on the island rookery are known to forage in the marsh habitats found on the western side of Mustang Island.

Migratory Species:

The preserve’s mudflats are ideal wintering habitat for piping plovers and other shorebirds. The aforementioned shorebirds and abundant waterfowl are an attractive food source for peregrine falcons during winter. Northern pintails, redheads, common goldeneyes and buffleheads are commonly recorded waterfowl on the preserve.

Geomorphic Features:

The Shamrock Island Management Complex includes a natural island in Corpus Christi Bay and a portion of Mustang Island (a coastal barrier island)

Ecosystem Function:

Shamrock Island and its associated barrier island marshes provide a variety of ecosystem function including: erosion protection, nursery, foraging, and resting areas for many fish and wildlife species. The marshes and seagrass beds on the site are very productive and provide important detrital input to Corpus Christi Bay.

Uniqueness of Natural Community:

The Shamrock Island Management Complex includes one of the largest colonial waterbird rookery islands on the Texas coast.

Current and Potential Use of the Site

Existing or Potential Educational Use:

Currently many institutions such as Texas A&M University and The University of Texas as well as other organized groups and partners use the site for educational purposes.

Recreational Use:

Wildlife observation and photography, recreational fishing, canoeing and kayaking.

Commercial Use:

Prior to ownership, the Conservancy developed a positive partnership with Bristol Resources, an oil and gas operator on the island. Working together, successful in cleanup and restoration of a portion of the island damaged by past oil and gas extraction was completed. All steel tanks and most of the remaining oil and gas collecting equipment were removed from the island. A sludge pit was restored by removing contaminated soil and planting the disturbed site with native plant species. Bristol also installed a boat docking facility for Conservancy use in patrolling, protecting and providing stewardship to the island. Recently, all interests and assets of Bristol Resources on the island were transferred to Chapparal Energy of Oklahoma. The Nature Conservancy continues to work cooperatively with these new operators on issues of compatible uses of the island’s resources.

Private Use:

Private third-party interest hold mineral right underlying the site so the The Nature Conservancy continues to work cooperatively to insure compatible uses of the sites resources.

Management Status

Land Ownership:

The Nature Conservancy of Texas acquired Shamrock Island in 1995, through a partnership with the Texas General Land Office. The Conservancy owns and manages the preserve while the General Land Office holds a conservation easement on the island. The Francine Cohn Preserve was acquired in April 2000 following a generous donation by Mr. Marcus Cohn of 22 acres followed by the purchase of an adjoining 278 acres from a private landowner with the vital assistance of the Coastal Bend Bays and Estuaries Program, and Citgo. Since April 2000 Shamrock Island and The Francine Cohn Preserve has been managed as a single complex.

Existing Designations:

Shamrock Island and The Francine Cohn Preserve are both designated as Portfolio Sites and Action Sites in the Nature Conservancy’s Gulf Coast Prairies and Marshes Ecoregional Plan

Management Status:

The Shamrock Island Management Complex is managed for the protection of this important colonial waterbird Rookery Island and adjacent feeding area.

Existing Monitoring Activities:

The Shamrock Island Shoreline Protection, Wetlands Restoration Project was completed in spring of 1999 and was the recipient of the 1999 Coastal America Partnership Award. In November 2000 the Texas General Land Office funded an eighteen-month post-construction topographic and hydrographic survey of the wetland restoration area, feeder beach area, and geotubes at Shamrock Island. The purpose of the survey and acquisition of aerial photography was to assess the performance of the geotubes, feeder beach, and wetland restoration area. The survey found that overall, the project was performing as designed. However, the survey found that one geotube’s crest elevation had decreased in one place. It also found that the area available for planting within the wetlands restoration area had decreased by about 10% and the total volume of added fill for the feeder beach had decreased since construction. The report recommended continued monitoring of the project to track changes to the geotubes, wetlands, and feeder beach.

On October 29, 2001, representatives from Texas Parks and Wildlife Department, Texas Nature Conservancy, U.S. Fish and Wildlife Service, Coastal Bend Bays and Estuaries Program, and Shiner Moseley and Associates, Inc. conducted a site visit to Shamrock Island to review the current condition of shoreline stabilization improvements and wetlands restoration area. During the site visit, it was observed that the geotube shroud is damaged in places. Maintenance/replacement of the shroud is needed to protect the exposed polyester of the geotube from UV degradation. Also, there are two areas where the geotube crest height has decreased, making the geotube submergent in those areas. Further investigation of these conditions is needed to determine the level of maintenance and/or remedial action necessary. It appears that more than 50% of the total feeder beach originally placed is depleted and plans to re-nourish the feeder beach are needed. The representatives also recommended that the planting area in the wetlands restoration area be expanded by mechanically placing more fill into the area to create more area suitable for Spartina alterniflora.

Acquisition Potential:

Potential exists to acquire additional land on Mustang Island for inclusion into the site.

Management Needs:

Although efforts to protect Shamrock Island have begun, erosion is still a major concern. A better understanding of the geophysical processes causing the erosion along with specific recommendations to address this problem while maintaining the integrity of the colonial nesting habitats is needed.

Site Viability

Threats to Ecological Integrity:

From 1956 to 1997 Shamrock Island lost about 25% of it’s surface area. Erosion is the greatest threat to the island.

Management Potential:

Developing sound science based solutions to erosion of Shamrock Island and the implementation of these strategies is the priority management action.

Sources of Information

EVALUATION OF LONG-TERM HABITAT AND COLONIAL WATERBIRD DYNAMICS OF SHAMROCK ISLAND, NUECES COUNTY, TEXAS, by Carolyn Gorman and Elizabeth H. Smith

Restoration Plan for Chiltipin Creek Oil Spill of January 7, 1992 San Patricio County, Texas. Prepared by: Texas General Land Office, Texas Parks and Wildlife Department, Texas Natural Resource Conservation Commission, United States Department of Interior.

Notes on a Brief Botanical Survey of the Cohn Preserve, Nueces County, Texas, 26 October 1999. By William R. Carr, The Nature Conservancy of Texas