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Steelhead
Facts
Steelhead
Restoration and Management Strategies
Fish
experts are calling for a new way of managing steelhead and rainbow
trout in our streams. "Historically, there's been a big gap in
the way we manage resident rainbow
trout and anadromous
steelhead," says Department of Fish and Game steelhead biologist
Dennis McEwan, one of the State's greatest authorities on salmonids.
"The old paradigm was to separate resident and anadromous fish
and manage them separately. But genetic testing has shown no differences
between resident and anadromous fish occupying the same stream
- geography is the most important factor." In other words, native
resident and anadromous fish from the same stream are closer genetically
than steelhead from one stream are to steelhead from another.
McEwan
says we should be managing steelhead - resident and anadromous
- based on their unique biology. Steelhead do not form discrete
populations within streams, says McEwan. Instead, they freely
interbreed, and adults can produce young that behave differently
than they do: migratory fish can produce resident trout and vice
versa. While some steelhead migrate to the ocean, others just
move down to the estuary, while still others merely move up and
downstream. This flexibility allows the population to survive
in the upper reaches of a stream during extreme conditions, such
as droughts, when the lower reaches dry up and lose their connection
to the ocean.
These
survival strategies also enable "sink" populations - those that
may exist only for a few decades - to act as a buffer against
the wholesale extinction of a particular population, says McEwan.
While source populations - those that persist for millennia -
are found in the larger river systems, sinks are often found in
smaller, sometimes seasonal streams. Although local extirpations
(or extinctions) of sink populations are a natural phenomenon,
so is recolonization from the source population, says McEwan.
But with the extensive human plumbing of rivers - dams, flood
control structures, diversions, etc. - limiting fish passage,
extirpations have been greatly accelerated and opportunities for
fish to recolonize severely reduced. Contrary to the traditional
view that to be protected, steelhead must be a "permanently reproducing
population," a better way of managing steelhead, says McEwan,
would recognize that resident rainbow trout help maintain the
larger population by adding genetic diversity and diverse survival
strategies, and would offer them the same protection given to
their more mobile cousins - or brothers. Unlike migratory steelhead,
rainbow trout are not protected under the Endangered
Species Act.
Recovery
plans for steelhead should also focus on reestablishing links
within populations - and genetic flow between resident rainbow
trout and steelhead - by restoring access to the upper reaches
of streams. Says McEwan, "Since California rainbow trout have
evolved in the face of extreme habitat conditions, they are tremendously
resilient to man-made disturbances. But this resilience absolutely
depends on having access to the upper reaches of our rivers, where
habitat conditions are more stable and conducive for fish for
surviving the 'bad' years."
- courtesy of author Lisa Viani (a version of this article
first appeared in the April 2001 issue of ESTUARY, published by
the San Francisco Estuary Project.)
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