Marsh - Anadromous Fish Habitat
Anadromous Fish Habitat
|Dam on the Saugatucket River, Wakefield,
Courtesy: D. Yozzo, Barry Vittor & Associates
Dam removal is the best solution to restoring streams
and anadromous fish runs, as it permanently restores the waterway
and does not require ongoing operation and maintenance of fishways
(Connecticut River Watershed Council, Inc. 2000). However, dam removal
is not always feasible due to existing land uses, industrial and residential
infrastructure in the vicinity of a dam or immediately downstream,
and concerns regarding increased stream flows and erosion and sedimentation
patterns. Fish ladders, or fishways can be used to bypass blockages;
this is the most commonly applied solution to restoring fish passage
over impediments in Rhode Island. Dams which no longer provide a
function but which cannot be completely removed can often be notched
or partially breached to allow fish access upstream.
Fish Ladders | Fish
Lifts (Elevators) | Stocking
|Pallisades fish ladder in
Courtesy: D. Yozzo, Barry Vittor & Associates
Fish ladders consist of a series of gradually inclining steps with
resting pools located at regular intervals. These provide the fish
with a means for active migration that simulates natural river conditions.
Most ladders are designed with a 10 percent grade. If a fish ladder does
not provide sufficient water, fish will not be attracted to the
fishway. If too much flow is generated, fish will be deterred from
using the fishway.
A steeppass fishway
is a prefabricated aluminum chute with vanes along the sides and
bottom that create turbulence, which lowers water velocity. Steeppass
fishways are particularly well-suited for small dams, and they are
relatively easy to install and maintain.
fishway is a type of fish ladder designed with a series of sloped
channels. The fishway can be constructed with an overall slope of
10 to 25 percent. Wooden baffles are placed at regular intervals, and are
usually constructed with a 45 percent slope. A narrow entrance creates
high water velocity to attract fish. Resting pools may be located
between long segments of the fishway. A denil fishway is larger
than a steeppass fishway, and is best for medium to large dams.
A pool-and-weir fishway
is a series of individual pools separated by walls or weirs. These
structures may be constructed of stone, wood, or concrete. This
type of fishway is suitable for both small and large dams (Connecticut
River Watershed Council, Inc).
Fish ladders can be built of concrete, wood or aluminum. Selection
of the appropriate ladder type and construction material depends
on the target species, dam size, and anticipated project cost (Connecticut
River Watershed Council, Inc. 2000). If a fish run restoration project
is aimed at several target species, ladders should be designed for
the weakest swimmer. Among the target species considered for restoration
in Rhode Island, salmon are the strongest swimmers, followed by
river herring, and American shad. Shad can be blocked by an obstruction
only one foot high. Herring are unable to jump over obstructions
and require a moderately sloped fishway (e.g., steeppass
or denil). Salmon and trout can jump, and will ascend small waterfalls.
The following considerations will help determine the selection
of the type of fish ladder to be used at a particular site.
- Which species are likely to be found in a particular tributary
or at that particular blockage?
- Is the design of fishway appropriate for the swimming capabilities
of the species?
- What water velocity will attract a fish to a fishway without
inducing it to spawn halfway up the fishway?
- In which part of the river are the target species likely to
- How many fish will need to pass the blockage and use the fishway?
- Is the method cost effective? Is it durable?
Fish Lifts (Elevators)
A mechanized lift provides passive migration of fish over dams to
spawning areas. Fish swim into chambers at the base of the dam,
guided by currents, and the chambers are mechanically lifted up
and over the dam, depositing fish on the other side. Lifts have
been used to overcome large dams in other states, such as the Susquehanna
River and its tributaries in Pennsylvania. Another well-known example
is in operation on the Connecticut River at Holyoke, Massachusetts,
but none have yet been constructed in Rhode Island.
For information on fish run restoration on the Susquehanna River
and drawings of how fishlifts work, visit the Safe
Harbor Water Power Corporation Web site.
Often, stocking of adults and juveniles is employed in fish run
restoration projects to supplement dwindling local stocks, to reintroduce
fish in systems in which they have been completely extirpated, or
to simply accelerate the rate of recovery in fisheries undergoing
restoration. Live adult herring or shad are trapped in East Coast
rivers that support healthy, sustainable runs and are released into
the waterway to be restored. In some cases, where the system still
supports a remnant run, adults can simply be trapped in lower reaches
of a river below the impediments, and transported to locations
above the impediments to be breached or overcome.
In some cases, particularly when a stock has been completely eradicated
within a stream or river, hatchery production of young fish (larvae
and juveniles) is used for reestablishment. Eggs are collected
from adults spawning in other river systems. These eggs are fertilized
in a laboratory and reared to the juvenile stage. The juveniles
are then introduced into the river system undergoing restoration
(within which water quality and impediments to migration have been
addressed) to restore the historic run.
Stocking was used in the restoration of the historic herring run
in the Narrow River to Carr Pond (upstream of Gilbert Stuart's Birthplace).
Breeding adult herring from the Connecticut River and tributary
streams in Massachusetts were stocked in Carr Pond in the mid-1990s.
The original brood stock returned to their native streams after
spawning, however their offspring returned to the Narrow River and
Carr Pond in successive years. The current annual herring run at
Gilbert Stuart's Birthplace exceeds 300,000 individuals (Gilbert Stuart Museum 2002).
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Connecticut River Watershed Council, Inc. 2000. A fishway for
your stream: providing fish passage around dams in the Northeast.
The Connecticut River Watershed Council, Inc., Easthampton, Massachusetts.
to order copies of this publication.
Gilbert Stuart Museum. 2002. "River Herring Restoration" Web page (http://www.gilbertstuartmuseum.com/riverherringpage.htm).
Saunderstown, Rhode Island.
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