Hydropower Dams Hamper Migrating Fish Despite Passage Features, Study
By University Communications, January 16, 2013
Facilities in the northeastern U.S. fail to allow passage of migrating
fish from the sea to their spawning grounds, scientists say.
Major hydropower dams in the northeastern United States, constructed
with state-of-the-art features designed to allow migratory fish to
pass through them on their way to spawn upstream, have failed in that
regard, raising questions that should be addressed as more dams are
These findings were reported in a study published today in the journal
A team of ecologists and economists, led by J. Jed Brown of the Masdar
Institute of Science and Technology in Abu Dhabi in the United Arab
Emirates, reported that despite the presence of fish-passage
facilities that were built into the dams, the actual numbers of fish
that passed through them over several decades were only tiny fractions
of targeted goals.
Brown completed his doctorate in renewable natural resources at the
University of Arizona under the direction of Edward Glenn, a professor
in the department of soil, water and environmental science at the UA
College of Agriculture and Life Sciences.
ï¿½It may be time to admit failure of fish passage and hatchery-based
restoration programs and acknowledge that ecologically and
economically significant diadromous species restoration is not
possible without dam removals,ï¿½ Brown and his colleagues wrote.
The three large river systems studied ï¿½ the Merrimack, Connecticut and
Susquehanna ï¿½ are historically important rivers for a suite of fishes
that migrate from the sea to rivers; they are called diadromous fishes
by scientists and include species such as sturgeon, salmon, shad,
river herring and eel.
ï¿½Once these rivers supported tens of millions of pounds of biomass of
these species and provided valuable protein to
a growing nation,ï¿½ said Karin Limburg, a
fisheries ecologist at the SUNY College of Environmental Science and
Forestry in Syracuse, N.Y.
Today the river systems contain hundreds of dams. The dams with the
largest impacts on the fish populations are
those constructed on the main stems of the
rivers for hydropower generation. There are four on the Susquehanna,
including one less than nine miles from its mouth at the head of the
Chesapeake Bay, more than 10 on the Connecticut and five on the
Using publically available data collected by various agencies since
the 1960s, the research team shows that these state-of-the-art fish
passage facilities have been unsuccessful. Some migratory species,
such as sturgeons, do not pass through at all. But even the species
that do make it through do so in numbers far less than stated targets.
In recent years, for example, the number of American shad, which was
once one of Americaï¿½s premier food fish, that passed through the dams
has hovered around 2 percent of the target in the Merrimack River and
close to zero percent of target in the other two rivers. System-wide
passage efficiencies, defined as passage from the most downstream dam
in a river up past the uppermost main stem dam with fish passage
facilities, hover at less than 3 percent. Although some fish spawning
does occur downstream of the lowest dams, most of these migratory
species require habitat above the farthest upstream dam.
River herring, a term used to describe both blueback herring and
alewife, are important migratory forage fish, which have been proposed
for listing under the federal Endangered Species Act.
ï¿½These dams are contributing to reduced resilience of not only shad,
but all diadromous species,ï¿½ said Adrian Jordaan of the University of
Massachusetts, Amherst. ï¿½The result is that other factors including
climate change will have a greater impact on these populations that
are at fractions of their historical levels.ï¿½ For example, restoration
targets for river herring vary from several hundred thousand to
millions of fish ï¿½ however, in recent years, river herring returns on
these rivers have averaged less than 1,000 fish.
ï¿½The consequences of the use of these failed technologies include
declines in diadromous species, but also an odd, self-perpetuation of
attempts to mitigate dam impacts by continuing restoration programs
despite their inability to show success,ï¿½ said John Waldman of Queens
College. ï¿½Not only are these losses felt locally, possibly with major
ramifications to fishery and biodiversity resources, but in fact they
translate into lost marine production and weakened marine food webs.ï¿½
The authors note that ï¿½ ironically ï¿½ at one fish passage facility with
an educational center, no fish passed in a typical year.
The authors support innovative solutions to this quandary, inviting
more scrutiny to finding alternatives to main stem dams. In the state
of Maine, for example, a creative solution developed by a broad
coalition was to purchase two main stem dams on the stateï¿½s largest
river, the Penobscot, but compensate the electric company with
alternative power generation in tributaries considered less critical
for fish reproduction.
The researchers say the case study serves as a cautionary tale not to
count on fish passage facilities to mitigate dam projects, even as
many developing nations look to their undammed rivers ï¿½ the Amazon and
the Mekong, among others ï¿½ as valuable potential sources of hydropower.
ï¿½Electricity from hydropower dams is considered mature technology that
is seen as ï¿½green energyï¿½ because it does not generate greenhouse
gases,ï¿½ said Brown, the lead author.
ï¿½Although hydropower dams are criticized for obstructing the movement
of fishes and other creatures, many hydropower dams have fish passage
facilities of one sort or another. These passage facilities appear to
create a ï¿½win-winï¿½ situation that allows us to enjoy both
hydroelectricity and healthy fish populations. The problem is it
doesnï¿½t seem to work.ï¿½
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