HELPING COHO SURVIVE THE WINTER
Habitat Restoration A Key To Salmon Recovery
COHO NEED SAFE HAVEN DURING THE WINTER
Wild populations of coho salmon are at such low numbers in most
areas of Northern California, Oregon, and Washington, that the
species has been proposed as threatened under the Endangered Species
Act. The recreational and commercial fishing industries, once
making multi-millions of dollars from coho fishing, have been
severely hurt by the complete restrictions on coho fishing the
past few years. Research by the Oregon Department of Fish and
Wildlife has shown that one factor limiting salmon survival is
the lack of appropriate habitat for coho salmon during the winter.
Because this winter habitat is lacking, only 10-20% of the juvenile
coho salmon present in streams at the end of summer make it through
the rainy season to smolt (migrate to sea) the next spring. Winter
habitat is the area in the stream and surrounding area where young
coho can escape from the strong water currents and floods of the
rainy season. Large trees and branches in the stream, log jams,
flooded wetlands, side channels & pools, and beaver ponds
all can provide refuge. Without such areas, the young salmon get
washed downstream and will not survive. By restoring winter habitat,
the survival of young coho salmon can be increased and the corresponding
recovery of the adult salmon runs better assured.
GOOD HABITAT IS HARD TO FIND
Many types of human activities, including forestry, agriculture,
and urbanization, have altered the availability of winter habitat
for fish. In the past, biologists thought that logs in the stream
were obstructing fish passage and had logging companies remove
them. Now we know that large logs in the stream as well as streamside
trees and their overhanging roots and branches are critical for
fish survival. To create pastures and developable land, streams
were straightened and rip-rapped (covered by rock to stop erosion),
dikes were built, wetlands were ditched and drained, beavers killed,
and tide gates installed. Now we know that the stream meanders,
oxbows, side channels, beaver ponds, and flooded wetlands are
filled with small coho seeking refuge during the winter. As towns
and cities grew areas were paved, wetlands filled, run-off channeled
into storm drains, and streams straightened and put through culverts.
Now we know that these changes have resulted in increased water
velocities and the severity of floods. We find too that the culverts
have blocked passage of young fish trying to find their way to
calmer waters during storms and floods.
RESTORATION EFFORTS CAN PAY OFF QUICKLY
Fortunately there are both short term and long-term things that
can be done to restore winter habitat. In the short-term, strategically
adding complex woody materials (such as old Christmas trees and
the trees from tree thinning operations) in areas of existing
deep pools, using large logs, rootwads and boulders to create
new pools, and building quiet off-channel pools can provide a
quick boost in juvenile survival rates. Assuring that the young
fish can also avail themselves of existing good habitat--for example
making sure the fish can get through tide gates and culverts during
the winter to slower- water areas, can also help boost salmon
survival. In the long term replanting trees in streamside buffers,
fencing areas where livestock are present, allowing beaver to
help re-establish pools, and de-channeling some areas to allow
the stream to re-establish its meander will create conditions
favorable to coho survival. The construction of artificial wetlands
and other storm water retention systems will also help improve
salmon survival by slowing run-off and reducing the pollutants
entering the streams and rivers.
Adapted by Pacific States Marine Fisheries Commission from information
provided by Oregon Department of Fish and Wildlife
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Revised 3/10/97
