EPA's Vessel General Permit and Small Vessel General

Chinook salmon feed on a variety of prey organisms depending upon life stage. Adult oceanic
Chinook salmon eat small fish, amphipods, and crab megalops (Healey 1991). Fish, in particular
herring, make up the largest portion of an adult Chinook salmon’s diet. In estuaries, Chinook
salmon smolts tend to feed on chironomid larvae and pupae, Daphnia, Eogammarus, Corphium
and Neomysis, as well as juvenile herring, sticklebacks and other small fish. In fresh water,
Chinook salmon juveniles feed on terrestrial and aquatic insects and their larvae, including:
dipterans, beetles, stoneflies, chironomids, and plecopterans (Healey 1991).
Threats
Natural Threats. Chinook salmon are prey for pelagic fishes, birds, and marine mammals,
including harbor seals, sea lions, and killer whales. There have been recent concerns that the
increasing size of tern, seal, and sea lion populations in the Pacific Northwest may have reduced
the survival of some salmon species.
Anthropogenic Threats. Salmon survive only in aquatic ecosystems and, therefore, depend on
the quantity and quality of those ecosystems. Salmon along the west coast of the U.S. share
many of the same threats. Therefore, anthropogenic threats for all species and populations are
summarized here. Salmon have declined under the combined effects of multiple anthropogenic
stressors. The main drivers of the decline are known as the four “H”s: habitat loss, hatcheries,
hydropower, and harvest. Examples of these include fishery over-harvest, competition from
hatchery fish and non-native species, the effects of dams, water diversions, destruction or
degradation of riparian habitat, and land use practices that destroy or degrade wetland and
riparian ecosystems (Buhle et al. 2009).
Population declines have resulted from several human-mediated causes, but the greatest negative
influence has likely been the establishment of waterway obstructions such as dams, power plants
and sluiceways for hydropower, agriculture, flood control and water storage. These structures
have blocked salmon migration to spawning habitat or resulted in direct mortality and have
eliminated entire salmon runs as a result. While some of these barriers remain, others have been
reengineered, renovated or removed to allow for surviving runs to access former habitat, but
success has been limited. These types of barriers alter the natural hydrograph of basins, both
upstream and downstream of the structure, and significantly reduce the availability and quality of
spawning and rearing habitat (Hatten and Tiffan. 2009). Many streams and rivers, particularly in
urban or suburban areas, suffer from streamside development, which contributes sediment,
chemical pollutants from pesticide applications and automobile or industrial activities, altered
stream flows, loss of streamside vegetation and allochthonous materials to name a few. These
factors can directly cause mortality, reduce reproductive success or affect the health and fitness
of all salmon life stages.
Changes in hydrological regimes are closely linked to salmon abundance (Hicks et al. 1991).
From studies that have examined the effects of changes in land use patterns, we know that
changes in hydrology can profoundly affect salmon abundance and the amount and availability
of quality habitat. Hydrology is strongly correlated to early survival and can lead to the
displacement of young fish as well as altering immigration and emigration timing which impacts
the relative abundance of salmon within a watershed, as well as the relative abundance of ageclasses
(Hicks et al. 1991, Gregory and Bisson 1997). Such ecosystem changes are also likely to
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