"The effects of dams on salmon
in New England rivers
Babcock's Rapids, Kennebec
River, Augusta, Maine.
June 2003. Restored to life after removal
of the Edwards Dam (two miles downstream) in summer 1999. Photo by Timothy Watts.
DAMS MUST GO TO SAVE ATLANTIC SALMON
In a long awaited research report, the National
Academy of Sciences has declared that
dams must be removed on Maine's Atlantic
salmon rivers if the species is to be saved from
extinction in the United
States of America.
Excerpts from the Academy's 260 page report, Atlantic Salmon in Maine,
are as follows:
"Dams are a major cause of salmon declines worldwide .... The committee
regards dams as a serious problem for successful restoration of salmon on a
statewide scale because the larger drainages have greater potential to support
large salmon populations."
"Although fish-passage facilities can
alleviate the difficulties that adults have in upstream migration, the effects of dams on the downstream migration of smolts
has been recognized only recently, and they are more difficult to
reverse. The slow-moving pools behind dams confuse smolts
during migration, increase the energetic costs of their movement, and can
increase predation on them. The dams can injure smolts
or block their passage. Although smolts do swim,
their travel time to the estuary can be greatly increased as a result of dams,
as has been shown on the Columbia River system in the Pacific
Northwest (NMFS 2000b). Although the western dams are larger than
those in Maine, effects documented in the West
are likely to occur to some degree on dammed streams in Maine.
"The second effect needs wider recognition. By creating pools behind them,
dams change habitat by eliminating flowing water and riffles. They flood
riparian habitats, and they change the patterns of sedimentation and erosion.
Dams usually cause changes in water temperature and chemistry, and reservoirs
behind dams are often stratified, while undammed
rivers are usually not (American Rivers et al. 1999, Heinz Center 2002.) In
addition, the large woody debris, gravel and sediment that were formerly
carried down the river and that provided spawning and rearing habitat, as well
as cues that helped adults to return home to their natal streams, are now
stopped by dams. As a result, these altered habitats become less suitable for for spawning and juvenile rearing. Rivers behind dams
become pools, more like lakes than rivers. Most
anadromous salmonids are not adapted to such
habitats. Other species of vertebrates and invertebrates that can thrive in
lakes proliferate and thereby change the prey resources available to salmon, as
well as the number and kinds of their competitors and predators."
"Findings and Recommendations
The decline of Atlantic salmon populations in Maine has been pervasive
and substantial over the past 150 years, despite some periods in which they
increased in numbers. The decline has brought them close to extinction in
recent years. The combination and interaction of factors influencing salmon
populations have been changing as well. Although salmon have declined over much
of their natural range in Europe and North America in recent decades,
suggesting that some factors affecting them operate over large areas, the
severity of declines in Maine
warrants special attention. Maine's rivers and streams once had the capacity to
support much larger salmon populations than they do now, so the potential
exists to substantially increase the populations of wild salmon in Maine. In other words,
rehabilitating salmon populations in Maine
is challenging but appears possible."
"Dams appear to be the single most
important class of impediments to salmon recovery that can be influenced by
human actions in the short and medium terms."
"The evidence from over 130 years of
stocking leads to the conclusion that hatchery production has not rescued
Atlantic salmon in Maine.
The evidence does not allow an objective assessment of whether, or to what
degree, hatcheries have slowed the decline of Atlantic salmon in Maine. There has never
been an adequate assessment of whether stocked salmon, when they return to
spawn in Maine's
rivers, successfully contribute to the next generation. Reliance on hatcheries
as the sole or primary intervention will not be sufficient to prevent
extinction for very long.
"Urgently Needed Actions
There is an urgent need to reverse the decline of salmon populations in Maine if they are to be
saved. Other than the Penobscot River, only 80 adult salmon were recorded to
have returned to Maine's
rivers in 2002. The serious depletion of salmon populations in Maine underscores the need to expand rehabilitation
efforts to as many of Maine's
rivers as possible. Since most Maine salmon
are now in the Penobscot River, that population should be a primary focus for
rehabilitating the species in Maine.
The committee recommends the following urgent actions:
· A program of dam removal should be started. Priority should be given to dams
whose removal would make the greatest amount of spawning and rearing habitat
available, which means that downstream dams should be considered for removal
before dams upstream of them. In some cases, habitat restoration will likely be
required to reverse or mitigate some habitat changes caused by a dam,
especially if the dam is many decades old. The recent agreement to remove two Penobscot River dams (Richardson 2003) is
· No anadromous Atlantic salmon of any life stage should be stocked in
rivers that have populations of wild Atlantic salmon unless those rivers are
specifically identified as part of a hatchery-recovery program that uses
river-specific stocks. Stocking of non-native fish species and landlocked
salmon also should be avoided in those rivers. Other rivers that once supported
wild Atlantic salmon runs, but which lack them now, will probably become
repopulated by strays from nearby streams if populations in those nearby
streams recover. The advantages over stocking of such natural repopulation,
which would be more likely to lead to local genetic adaptation, should be given
serious attention before any decision is made to stock streams that currently
lack wild Atlantic salmon runs."
ANNOUNCING THE NAS REPORT:
Date: Jan. 20, 2004
Contacts: Bill Kearney, Director of Media Relations
Patrice Pages, Media Relations Officer
Christian Dobbins, Media Relations Assistant
Office of News and Public Information
202-334-2138; e-mail <firstname.lastname@example.org>
FOR IMMEDIATE RELEASE
Urgent Statewide Action Needed to
Serious Depletion of Atlantic Salmon in Maine
WASHINGTON -- Urgent actions are needed if the
once-abundant Atlantic salmon in Maine
are to be replenished, says a new report from the National Academies' National
Research Council. These rehabilitation efforts are needed statewide to preserve
Maine's population of the fish, which
constitutes most of the Atlantic salmon population in the United States.
"The decline of Atlantic salmon populations in Maine
has been pervasive and substantial over the past 150 years, bringing them close
to extinction in recent years," said Michael T. Clegg, chair of the
committee that wrote the report, and professor of genetics, University of California,
"Comprehensive, statewide action should be taken now to ensure their
survival. And a formalized decision-making approach is needed to evaluate
options, establish priorities, and coordinate plans for conserving and
restoring the salmon."
Populations of Atlantic salmon have declined drastically, from an estimated
half million adult salmon returning to U.S. rivers
each year in the early 1800s to perhaps as few as 1,000 in 2001. Atlantic
salmon were listed in 2000 as endangered under the federal Endangered Species
Act. Despite the intentional introduction of more than 100 million
hatchery-raised salmon and the escape of an unknown number of pen-raised salmon
into the wild over the past 130 years, salmon populations have never been
smaller. The wild North American Atlantic salmon remain clearly genetically
distinct from fish bred in captivity, according to an interim report from the
committee in January 2002.
Atlantic salmon are adapted to two very different environments. The young hatch
and grow for one to three years in freshwater rivers and streams before
migrating to sea. At sea, the salmon mature for two to three years and then
return to the same streams to lay their own eggs. While many of the adults die
after spawning, some migrate back to sea and make another return trip to spawn
If these migrating salmon are to survive, a program of systematic dam removal
should start immediately, the report says. Dams on Maine's rivers used for mills and other
purposes hinder the passage of adult and juvenile salmon and alter the rivers'
habitat. Some of the dams have also outlived their economic usefulness. The
report estimates removal costs to be between $300,000 and $15 million per year,
assuming a cost ranging from $100,000 to $3 million per dam and the removal of
three to five dams per year.
There is a high natural mortality after young salmon migrate from fresh water
to the ocean. Sulfates and other chemicals from the atmosphere that alter the
water chemistry of streams may be harming young salmon and increasing mortality
among fish making the transition from fresh water to salt water. The addition
of limestone to rivers and streams, known as liming, is a well-established
procedure that has had considerable success in counteracting acidification in
streams. It should be tried in some Maine
streams on an experimental basis as soon as possible, the reports
says. It is estimated that the initial cost of liming each stream would
be around $100,000, with subsequent costs of $50,000 to $100,000 per year for
each stream treated.
heavy reliance on hatcheries to increase its salmon population, these
facilities should be used sparingly, the report says. The focus of hatcheries
should be to preserve the genetic diversity of remaining wild salmon
populations by providing them with a secure place to grow if necessary.
Stocking rivers with hatchery-raised salmon remains an unproven way to boost
the fish population, the report adds, and additional research and scientific
guidance are needed.
The committee also recommended that Maine
avoid stocking its streams with salmon or nonnative fishes that may mate with
or crowd out wild salmon, or out-compete them for food. Improved monitoring of
water quality and better efforts to prevent farmed salmon from escaping also
are needed. In addition, a comprehensive decision-analysis approach should be
established to prioritize and coordinate efforts to restore the salmon. Fishing
has historically been a major source of mortality for Atlantic salmon, and fishing
for this species should continue to be prohibited in Maine, the committee added.
The study was sponsored by the National Fish and Wildlife Foundation. The
National Research Council is the principal operating arm of the National
Academy of Sciences and the National Academy of Engineering. It is a private,
nonprofit institution that provides science and technology advice under a
congressional charter. A committee roster follows.
Copies of Atlantic Salmon in Maine will be available later this winter
from the National Academies Press; tel. 202-334-3313 or 1-800-624-6242 or on
the Internet at http://www.nap.edu. Reporters
may obtain a pre-publication copy from the Office of News and Public
Information (contacts listed above).
[ This news release and report are available at http://national-academies.org ]