Salmon Habitat: It's All Downhill
The news that water flows downhill, and that fish depend on water,
won't come as a shock to anyone.
Yet these statements add up to an often-ignored fact about the
habitat needs of salmon (and everything else that depends on the
river). Salmon don't just live in water--they live in watersheds.
From the crest of the surrounding hills to the estuary at the
mouth, a river's watershed is the entire basin from which it gathers
its waters. As water percolates through the soil to the stream,
down the stream to the river, and eventually out to sea, its quality
and quantity is affected by everything it touches. Salmon are
affected by anything that happens is the watershed, even though
it may seemingly take place far from the river.
Salmon are affected by the water's temperature and nutrient content,
by the amount of sediment and oxygen it carries, by the rate of
its flow, and by other factors. All the natural systems in the
watershed--forests, meadows, wetlands, rock outcroppings--contribute
to the composition of the water.
The watershed determines the amount and force of the water in
the river, and the material carried down by its flow from higher
elevations. These factors shape the river bottom, which is another
important aspect of salmon habitat. Here, behind a large log,
the force of the stream may have dug a deep pool, where young
salmon shelter in the summer and returning adults rest on their
way to the spawning grounds. There, quiet eddies may have dropped
their loads of silt, creating mud which supports a marsh. In
another place, the river has deposited beds of gravel, which salmon
need for spawning. Some species prefer to lay their eggs in pea-sized
gravel, while other can use rocks as large as cantaloupes. The
particular types of habitat provided by the river depend on the
larger influence of the watershed.
Salmon evolved to cope with a sequence of habitats found in natural
watersheds. In a typical river system, tributary streams in the
upper reaches are heavily shaded by forests, which drop large
quantities of leaf litter and other organic material into the
water. Fallen trees in the stream trap spawning gravel on the
upstream side, and create plunge pools below where young fish
shelter and feed. Many of the aquatic insects available as prey
in these areas belong to a group know as "shredders",
which devour large bits of plant material floating in the water.
In the middle reaches of the river, the tree canopy opens up and
more sunlight falls on the water, prompting algae growth. Here
the prey species likely belong to groups know as "scrapers,"
which harvest algae from the rocks, and "collectors,"
such as net-spinning caddies fly larvae, which strain finer bits
of organic material from the water.
At its lower end, the river may wander in many channels across
its floodplain, providing a wealth of fish habitats in its wetlands,
sloughs and oxbows. In these marshes and estuaries, ocean-bound
salmon gorge on clouds of small crustaceans such as copepods and
amphipods.
All human activity in the watershed affects salmon habitat. Timber-cutting,
for instance, may remove shade and large streamside logs that
once fell periodically into the stream. Road construction and
agriculture often cause erosion, which in turn fills the water
with sediment that can clog spawning gravel. Culverts can block
fish passage and alter water flow. Removing creek meanders or
beaver dams and filling wetlands eliminates feeding areas and
the slow-water areas so important for sheltering young coho and
other salmon from the raging winter currents. Dams can slow the
force of the river's flow preventing it from cleansing sediment
from its bed and moving gravel downstream.
Because human beings live in watersheds, we are part of the salmon's
habitat. In many areas, small landowners, timber companies, fishermen,
environmentalists, farmers, tribal members, agency representatives,
and others are working together to restore watersheds and improve
salmon habitat. Often called watershed, these coalitions are
finding ways to put aside differences and pool resources to help
the salmon. These groups work together to assess the health of
their watershed, identify areas where restoration efforts can
best help the salmon, and seek out willing landowners to implement
habitat restoration projects.
Projects undertaken by watershed groups have included stream surveys,
tree planting (to provide shade along stream banks), road and
bank stabilization (to prevent erosion), culvert repair (to facilitate
fish passage--for both young and adult fish), placing logs in
streams (to create shelter and deep pools), side-channel construction
(to provide slow water areas for winter shelter), and cattle watering
and fencing (to keep cows and sheep out of streams). Participants
have included loggers, fishermen, agency personnel, civic groups,
environmentalists, and youth groups ...entire communities, taking
responsibility for their watersheds.
To learn more about watershed groups in your area, or for more
information on how you can assist salmon recovery efforts in the
Pacific Northwest, please write the Pacific States Marine Fisheries
Commission, 45 SE 82nd Drive, Suite 100, Gladstone, OR 97027-2522.
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Revised 3/10/97
