Rhode Island's Coastal Habitats
Marsh - Anadromous Fish Habitat
Anadromous Fish Habitats
History | Healthy
vs. Degraded | Fish Habitat Restoration
| Case Study |
|River herring run in the Gilbert Stuart
Brook, North Kingstown, May 2000
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,
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
|Slater Mill Dam, Blackstone River
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
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, Gilbert Stuart Brook
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
- Presence of fallen logs or boulders that provide habitat
- Indicators of good water quality, such as diverse benthic
- 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
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.
- 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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This site was created through a partnership
Coastal Resources Management Council
Narragansett Bay Estuary Program
Save The Bay®