Northeast Coastal Areas Study
Significant Coastal Habitats
Site 26 (CT)
I. SITE NAME: Lower Thames River System
II. LOCATION: The lower tidal reaches of the Thames River in southeastern Connecticut from New London and Groton at the mouth to Norwich.
TOWNS: New London, Groton, Uncasville,
Montville, Preston, Norwich
COUNTY: New London
STATE: Connecticut
USGS 7.5 MIN QUADS: New London, Conn 41072-31;
Uncasville, Conn 41072-41; Norwich, Conn 41072-51
USGS 30x60 MIN QUADS: New Haven 41072-A1;
Hartford 41072-E1
III. GENERAL BOUNDARY: The boundary of this site includes the river channel, waters and shoreline wetlands of the lower tidal reaches of the Thames River from the confluence of the Shetucket and Quinebaug Rivers a few miles north of Norwich to the mouth of the river at New London and Groton where it enters into the eastern end of Long Island Sound, a river length of approximately 19 miles (31 km). Specific areas of biological significance, in addition to the river itself, include the Mamacoke Island marshes, Horton Cove, Poquetanuck Cove marshes, Smith Cove, Greens Harbor and small rocky islands at the river mouth.
IV. OWNERSHIP/PROTECTED STATUS: Primarily Public Trust waters and State and private conservation and research lands. Connecticut College owns and manages Mamacoke Island Natural Area.
V. GENERAL HABITAT DESCRIPTION: Tidal river and associated wetlands, including tidal saltmarsh, dominated by cordgrasses (Spartina alterniflora and S. patens) at Mamacoke Island Natural Area, and protected coves. Tidal brackish marsh, an unusual vegetation/habitat type in the region, is characterized by such species as narrow-leaved cattail (Typha angustifolia), salt-marsh fleabane (Pluchea purpurascens var. succulenta) and mudwort (Limosella subulata), the latter a locally rare species.
VI. SIGNIFICANCE/UNIQUENESS OF AREA: Several of the shallow tidal coves and associated brackish marshes in the lower Thames River contain regionally significant concentrations of wintering and migrating waterfowl, especially of several species not commonly found elsewhere or in similar concentrations in the region. These include relatively large numbers of canvasback (Aythya valisineria), American wigeon (Anas americana), American black duck (Anas rubripes), gadwall (Anas strepera), mallard (Anas platyrhynchos), redhead (Aythya americana), common goldeneye (Bucephala clangula) and hooded merganser (Lophodytes cucullatus). Also found here are common and red-breasted merganser (Mergus merganser and M. serrator, respectively), and greater and lesser scaup (Aythya marila and A. affinis, respectively). Nesting and wintering here in increasing numbers are mute swans (Cygnus olor), a species which is becoming a problem throughout the region. Osprey (Pandion haliaetus) breed at several places along the river. Small rocky islets in the river mouth contain nesting populations of common and roseate tern (Sterna hirundo and S. dougallii, respectively), the latter a U.S. Endangered species. The river is an important anadromous fish corridor especially for American shad (Alosa sapidissima), Atlantic salmon (Salmo salar), Atlantic sturgeon (Acipenser oxyrhynchus), striped bass (Morone saxatilis), white perch (Morone americana), alewife (Alosa pseudoharengus), blueback herring (Alosa aestivalis), rainbow smelt (Osmerus mordax) and sea-run brown trout (Salmo trutta). It is also an important nursery and spawning area for winter flounder (Pseudopleuronectes americanus) and an overwintering area for striped bass. The lower river has significant shellfish beds, especially of hard-shelled clams (Mercenaria mercenaria) and soft-shelled clams (Mya arenaria).
VII. THREATS: Industrial, commercial and residential development along the river corridor impacts fish and wildlife populations and habitats largely through direct losses of habitat and degradations in habitat quality, particularly water quality. Heavy metal contamination, sewage, stormwater and waste discharges, shoreline marina development and dredging are all of concern in the Thames River aquatic environment. The river is reported to have significant water quality problems, particularly in certain upstream areas and at the mouth of the river.
VIII. CONSERVATION CONSIDERATIONS: Particular attention needs to be focused on restoring and protecting the water quality of the Thames River and its high value to fish and wildlife populations, especially anadromous fish and overwintering waterfowl. Protective measures should include stringent regulatory overview and enforcement of existing Federal, State and local environmental regulations, as well as developing and implementing environmentally sound planning and zoning policies and restoration programs.
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