Carbaryl, Carbofuran, and Methomyl - National Marine Fisheries ...

ground water and degrade water quality in the freshwater, estuarine, and coastal
ecosystems throughout the Pacific Northwest.
Coho Salmon
Description of the Species
Coho salmon occur naturally in most major river basins around the North Pacific Ocean
from central California to northern Japan (Laufle, Pauley et al. 1986). We discuss the
distribution, life history diversity, status, and critical habitat of the four endangered and
threatened coho species separately.
After entering the ocean, immature coho salmon initially remain in nearshore waters
close to the parent stream. Most coho salmon adults are three-year-olds, having spent
approximately 18 months rearing in freshwater and 18 months in salt water. Most coho
salmon enter rivers between September and February. However, entry is influenced by
discharge and other factors. In many systems, coho salmon and other Pacific salmon are
unable to enter the rivers until sufficiently strong flows open passages and provide
sufficient depth. Wild female coho salmon return to spawn almost exclusively at age
three. Coho salmon spawn from November to January, and occasionally into February
and March. Spawning occurs in a few third-order streams. Most spawning activity
occurs in fourth- and fifth-order streams. Spawning generally occurs in tributaries with
gradients of 3% or less.
Eggs incubate for about 35 to 50 days, and start emerging from the gravel within two to
three weeks after hatching. Following emergence, fry move to shallow areas near the
stream banks. As fry grow, they disperse upstream and downstream to establish and
defend territories. Juvenile rearing usually occurs in tributaries with gradients of 3% or
less, although they may move to streams with gradients of 4 to 5%. Juvenile coho
salmon are often found in small streams less than five ft wide, and may migrate
considerable distances to rear in lakes and off-channel ponds. During the summer, fry
prefer pools featuring adequate cover such as large woody debris, undercut banks, and
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