Fishes Shun Modern Dam Passages, Contributing to Population Declines/SciAm

http://www.scientificamerican.com/article.cfm?id=upstream-battle-fishes-shun-modern-dam-passages-population-declines&WT.mc_id=SA_CAT_ENGYSUS_20130221

Upstream Battle: Fishes Shun Modern Dam Passages, Contributing to
Population Declines
A river study in the U.S. Northeast has found that many fish species
are unable to use standard passageways to swim past dams on their
spawning runs

By Amy Kraft



Fishes may not need bicycles, as Gloria Steinem once suggested, but
elevators and ladders can come in handy. Since the 1960s the Federal
Energy Regulatory Commission has required dam builders to install
state-of-the-art fish passages on public waterways to help shad,
salmon and other species make their annual spring journeys upriver to
spawn. Hydropower dams have built inclined water channels called
ladders that fishes could swim through or elevators that use caged
buckets to lift fish up and over the dam. Although these passages are
monitored to ensure that fishes use them, a new study by ecologists
and economists shows that very few fishes actually pass through to
reach their spawning grounds, which exacerbates the decline in fish
populations.

Jed Brown of the Masdar Institute of Science and Technology in Abu
Dhabi and colleagues analyzed decades-worth of data on fish passages
in the Merrimack, Connecticut and Susquehanna rivers in the U.S.
Northeast. Roughly 2 percent of the targeted number of American shad
made it through Essex Dam on the Merrimack River in 2011 and close to
0 percent passed through dams on the Connecticut and Susquehanna.
Restoration targets for river herring, two species of silver-colored
fishes, are in the hundreds of thousands to millions of fish but in
recent years, less than 1,000 herring on average have returned to
these rivers from the ocean. Atlantic salmon numbers in the
Connecticut River have been similarly low despite decades of
restoration efforts.

One problem is that some fish passages are maladapted to the fishes
they were built to help. A 2001 report by the United States Geological
Survey showed that some fishes require specialized fishways because
they cannot maneuver on ladders, which are meant to simulate natural
rapids. For example, Atlantic salmon and river herring can easily
navigate fish ladders because they naturally plunge through
headwaters. Sturgeon and striped bass, on the other hand, do not
possess the same swimming ability. �If you have one bad dam or one bad
fishway, then the fish really aren�t moving up the river,� says
Theodore Castro-Santos, a research ecologist at USGS�s Conte
Anadromous Fish Research Center in Massachusetts. Castro-Santos said
that modern fishways are modeled after those installed on the
Bonneville Dam in the 1950s and have never been properly studied to
prove their effectiveness.

Even if fish do make it upstream to spawn, many have a hard time
getting back downstream. A 1994 study in Transactions of the American
Fisheries Society found that some fish species get killed attempting
to pass through turbines. �We�ve taken species that spawn more than
once in their lives and turned them into one-time spawners,� says John
Waldman, a professor of biology at Queens College, The City University
of New York, one of the authors of the new study.

The best solution to restoring fish populations, Waldman argues, is
dam removal. Past research on dam removal showed that it is effective
at restoring fish stocks and improving water quality. Studies on the
removal of Edwards Dam, a 280-meter-long hydroelectric dam on the
Kennebec River in Maine, found that fisheries have improved since its
take-down in 1999 and insect counts have increased, a good indicator
of improved water quality.

But dams are an important source of renewable energy, and removing
them is costly and can have sudden, dramatic impacts on ecosystems, as
this 2001 study in Hydrological Processes noted. Castro-Santos
believes that instead of removing dams, more robust research should be
conducted on fishways and the various fish species that move through
them. A 2012 study in River Research and Applications looked at how
the biological characteristics of different fish species determined
their propensity to use certain types of fishways. �In order to
evaluate the effectiveness of fishways, you need to know the behavior
of fish,� Castro-Santos says.

Waldman agrees that improved fishway technology could be the answer.
�If a dam can�t be taken down the best fishway possible is better than
any alternative,� he says.

For now the researchers hope that the study will help guide
authorities as they consider dam renewal licenses and as construction
begins on dam projects in the Amazon and Mekong rivers. �This is a
warning to the rest of the world where big dam projects are starting,�
Waldman says. �If it�s not working in the northeast U.S., it�s not
likely to work elsewhere.�
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