EPA's Vessel General Permit and Small Vessel General

Spawning migrations generally occur in the summer and fall; the precise spawn timing and
migration varies across populations. Generally, spawning runs consist of fish between 2 and 5
years of age. Fecundity is highly variable, and is correlated with body size and region (Salo
1991). Once they emerge from their gravel nests, chum salmon fry outmigrate to seawater almost
immediately (Salo 1991). This ocean-type migratory behavior contrasts with the stream-type
behavior of other species in its genus. Because of their small size chum salmon will form
loosely aggregated schools, presumably to reduce predation by swamping predators (Miller and
Brannon 1982; Pitcher 1986).
Generally, chum fry emigrate to estuaries between March through May where they forage on
epibenthic and neritic food resources. The timing of juvenile entry into sea water is commonly
correlated with nearshore warming and associated plankton blooms (Groot and Margolis. 1991).
As food resources decline and the fish grow, they move further out to forage on pelagic and
nektonic organisms (Simenstad and Salo 1982, Salo 1991). Migratory studies indicate that chum
salmon in their first year of life will typically maintain a coastal migratory pattern although the
pattern is variable as they mature at sea. At sea chum salmon feed on pteropods, euphausiids,
amphipods, fish and squid larvae (Salo 1991).
Threats
Natural Threats. Chum salmon are exposed to high rates of natural predation each stage of their
life stage and in particular during migration. Mortality at emergence or prior to emergence is
significant because eggs develop in the interstitial spaces in the stream gravel, and storm surges
that redeposit gravels and wash out eggs or introduce silt to the interstitial spaces can reduce egg
survival. Other factors that reduce egg survival and larvae development include low dissolved
oxygen, poor percolation and extreme cold or warm temperatures.
Anthropogenic Threats. Chum salmon, like the other listed salmon, have declined under the
combined effects of overharvests in fisheries; competition from fish raised in hatcheries and
native and non-native exotic species; dams that block their migrations and alter river hydrology;
gravel mining that impedes their migration and alters the dynamics (hydrogeomorphology) of the
rivers and streams that support juveniles; water diversions that deplete water levels in rivers and
streams; destruction or degradation of riparian habitat that increase water temperatures in rivers
and streams sufficient to reduce the survival of juvenile chum salmon; and land use practices
(logging, agriculture, urbanization) that destroy wetland and riparian ecosystems while
introducing sediment, nutrients, biocides, metals, and other pollutants into surface and ground
water and degrade water quality in the fresh water, estuarine, and coastal ecosystems throughout
the Pacific Northwest. These threats for are summarized in detail under the Chinook salmon of
this section.
Columbia River Chum Salmon
Distribution and Description of the Listed Species
The Columbia River chum ESU includes all naturally spawned populations of chum salmon in
the Columbia River and its tributaries in Washington and Oregon. Three artificial propagation
programs are part of the ESU.
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