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Rhode Island's Coastal Habitats

Seagrass - Salt Marsh - Anadromous Fish Habitat

Anadromous Fish Habitats

History | Healthy vs. Degraded | Fish Habitat Restoration | Case Study | Related Links
River herring run in the Gilbert Stuart Brook, North Kingstown, May 2000
River herring run in the Gilbert Stuart
Brook, North Kingstown, May 2000
Courtesy: NOAA

Anadromous fish runs in Rhode Island occur in rivers, streams, and adjacent areas that drain into coastal ponds, Narragansett Bay, and Block Island Sound. These systems are used by migratory fish to feed and reproduce. River herring (Alewife and Blueback Herring), Atlantic salmon, rainbow smelt, sturgeon, and American shad depend on passage upstream for survival. These anadromous fish spawn in fresh water, and mature and spend most of their lives in salt water. Conversely, American eels are catadromous fish, living in lakes and ponds as adults. They migrate downstream and eventually far out into the Atlantic, where they spawn and die in the Sargasso Sea. Their newly born young, less than an inch long, travel on ocean currents back to Rhode Island's rivers and streams.

Many of Rhode Island's rivers are blocked or obstructed by dams, weirs, tide gates, and other water-control structures. In addition to unobstructed passage through the water, migratory fish need healthy riparian areas whose vegetation provides cover, bank stabilization, and temperature regulation. Riparian vegetation also provides detritus (leaf litter, wood, etc.), which forms the base of the riverine food chain. Recreational and commercial fisheries benefit when river corridors remain healthy and passable to migratory fish (Save the Sound, Inc. 1998).

History and Impacts

Rhode Island once supported lucrative fisheries for Atlantic salmon, shad, and river herring (alewife and blueback herring). Prior to European colonization, Native Americans depended on the spawning runs of herring and salmon as staples. Accounts by Roger Williams, Verrazano, and other explorers and colonists describe the astounding productivity of the Bay's tributaries.

Slater Mill Dam, Blackstone River
Slater Mill Dam, Blackstone River
Courtesy: Narragansett Bay Estuary Program

During colonial times, dams were constructed throughout Rhode Island to harness water power. The advent of the Industrial Revolution in the late 18th century resulted in an increased number of larger dams. By the early 20th century, over 500 dams had been constructed in Rhode Island streams and rivers, with disastrous effects on anadromous fish runs. The Atlantic salmon fishery was lost by 1870. The river herring harvest was significantly depleted by 1930. Although commercial fisheries for these species are not currently viable, some runs still persist (e.g., Gilbert Stuart Brook and Annaquatuck River in North Kingstown).

Dams change stream flow patterns, encourage upstream siltation and physically prevent fish from reaching upstream spawning habitat. Many rivers and streams that flow through urban, residential, and farmed areas are subject to industrial and agricultural pollution, both from point and non-point runoff. Rivers and streams, which have been straightened and channelized (often with concrete beds), are lacking in potential fish spawning habitat. Additional impediments to spawning success may include blockage of migratory pathways by debris (e.g., construction materials, trash, brush piles, logs, etc.), blockage of smaller waterways by vegetation, culverts which may drain waterways or divert flow into rivers and ponds, and poor water quality. Water quality parameters critical to the successful movement of anadromous fish upstream include temperature, salinity, pH and dissolved oxygen (Durkas 1992)

It has been determined by DEM that there are at least 41 streams with potential for fish run restoration in Rhode Island and Massachusetts. Currently 18 streams support herring runs in Rhode Island but most are impaired to some degree and in need of restoration. Historically, at least 45 runs existed in the Narragansett Bay watershed. The most significant of these are the Taunton, Blackstone, Pawtuxet, and Ten Mile rivers.

Healthy vs. Degraded Anadromous Fish Habitats

In a healthy riverine system, fish migrate upstream to lay their eggs, and the eggs remain there until they develop into juveniles. In the fall, triggered by a decrease in water temperature and change in daylight, most of the juveniles begin their downstream run into more brackish water. Naturally functioning, stable stream systems promote the diversity and availability of habitats. Sinuous streams with slightly undercut banks, fallen logs, boulders and riffle/pool sequences provide some of the most diverse habitats for aquatic animals.

When a river or stream is blocked or altered, it will change the flow levels of the river or stream, sometimes allowing more sand and silt to build up on the bottom of the channel, covering previously used habitat for these fish species. Pollutants will accumulate in this sediment at the base of the obstructions. Obstructions can alter the water flow significantly, and in effect, they can change the bottom contours of the water body both upstream and downstream of the obstruction.

Fish ladder in the Gilbert Stuart Brook
Fish ladder, Gilbert Stuart Brook
Courtesy: NOAA

Riverine systems often run through urban and agricultural areas, and are often degraded by point and nonpoint source runoff when excess sediments, nutrients, and other pollutants clog streams and poison fish and wildlife. Stream banks that have been channelized and whose banks have been stripped of natural vegetation cannot provide the habitat necessary for the living resources of the water body (Chesapeake Bay Program 2000).

Dam removal increases fish spawning habitat upstream of the obstruction. Where dam removal is not an option, fish ladders can be used. These structures are designed to enable anadromous fish to bypass these blockages and return upstream to spawn. Blockages can also be removed, notched, or breached, particularly if the dam is small or in disrepair.

Healthy Fish Run Habitat Degraded Fish Run Habitat
  • Forested or thickly vegetated riparian zone bordering river or stream
  • Presence of fallen logs or boulders that provide habitat structure
  • Indicators of good water quality, such as diverse benthic community
  • Valuable in-stream species such as native brook trout
  • Vegetated banks
  • Gravelly or sandy sediments
  • Presence of an obstruction to fish passage
  • Channelized streambank
  • Unvegetated or undercut banks
  • Paved banks or riparian areas
  • Presence of floodwalls
  • Trash in the river or along the banks
  • Erosional areas (little gullies) along banks
  • Poor water quality
  • Presence of fish species representative of degraded habitats, such as carp
  • Contaminated sediments
  • Mucky sediments

Fish Habitat Restoration

Although fish run restoration has been around for a long time, its focus has evolved considerably in recent years. Twenty or thirty years ago, fish passage restoration was about managing particular species by allowing them to bypass an obstruction, usually a dam. Today, there is an awareness of the ecological role of fish runs, and an attempt to restore rivers and watersheds by re-establishing the annual migrations of groups of species.

Here in Rhode Island, the emphasis for restoration is on the herring tribe, particularly American shad, alewife, and blueback herring. The R.I. Department of Environmental Management (DEM) runs an Atlantic salmon restoration program on the Wood-Pawcatuck river system; however, most of the state's other rivers no longer have high enough water and habitat quality for salmon. Nevertheless, fish passage facilities can also benefit instream species such as brook and brown trout.

The most common fish passage facilities are fish ladders. Fish ladders can be built of concrete, timber, or aluminum. Some of the most common types are steeppass, denil, and pool-and-weir. Each is suitable for a particular species, stream size, or project cost. If a fish run restoration project is aimed at several target species, the ladders should generally be designed for the weakest swimmer.

Where practicable, dam removal is a better option than ladder construction because it restores the natural hydrology of the river, has the potential for many habitat and water-quality benefits, and because some anadromous fish such as smelts and sturgeon do not climb fish ladders. Federal, state, and non-profit agencies have begun promoting this approach to river restoration over the past several years, and several dams have been removed or breached in New England.

In Rhode Island, the legacies of industrialization and urbanization present special problems for dam removal. For example, on the Woonasquatucket River in Providence, the discovery of dioxin-contaminated sediments has spurred the reconstruction of an obsolete dam to prevent the release of contaminants into the river. Nevertheless, among the hundreds of dams in Rhode Island, most of which no longer serve their original purpose, there are undoubtedly many dams that it would be beneficial to remove. The R.I. Dams Database, developed by DEM and downloadable from this site, maps most of the dams in Rhode Island.

Anadromous Fish Run Restoration Case Study: Ten Mile River

Fishermen assisting a herring with passage into Omega Pond
Fishermen assisting a herring with passage into Omega Pond
Courtesy: Narragansett Bay Estuary Program

The Ten Mile River originates in Plainville, Massachusetts, and flows through the City of East Providence, Rhode Island, entering the Seekonk River at the head of Narragansett Bay. Historically, the Ten Mile River supported large runs of herring, salmon, and American shad; but like so many other New England rivers, dam construction in the 18th, 19th, and 20th centuries all but eliminated them. Remarkably, a remnant of the herring run has persisted with the help of local fishermen, who net the fish and toss them over the first dam to spawn in the waters of Omega Pond.

However, three dams completely prevent the fish from accessing significant spawning habitat: Omega Pond Dam, Hunts Mill Dam, and the Turner Reservoir Dam, all in East Providence. The city, therefore, has joined a partnership to restore herring and American shad to the Ten Mile River by providing fish passage over all three dams. DEM's Narragansett Bay Estuary Program and Division of Fish and Wildlife, Save The Bay, and the U.S. Army Corps of Engineers are developing engineering plans for the river restoration. Fish and Wildlife will stock the river with herring and American shad to re-establish the runs. It is estimated that the restored Ten Mile River will support a run of nearly a quarter-million fish per year.

Related Links

RI DEM 1999 - Protecting herring populations
RI DEM 2002 - Blackstone River Fisheries Restoration Plan (pdf)
RI DEM 2003 - Strategic Plan for the Restoration of Anadromous Fishes to Rhode Island Coastal Streams
Environmental News Network - Removing Dams, Restoring Rivers

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Chesapeake Bay Program. 2000. (http://www.chesapeakebay.net/tribs.htm). Annapolis, Maryland.

Durkas, S.J. 1992. Impediments to the spawning success of anadromous fish in tributaties of NY/NJ Harbor Watershed. American Littoral Society, Highlands, New Jersey.

Save the Sound, Inc. 1998. "The Long Island Sound Conservation Blueprint: Building the Case for Habitat Restoration In and Around the Sound." Stamford, CT. Save the Sound, Inc.

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Project Partner web pages - RIHRT, CRMC, NBEP, STB

This site was created through a partnership of the:

Coastal Resources Management Council
Narragansett Bay Estuary Program
Save The Bay®