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

conditions (unlike stream-type salmonids which depend heavily on freshwater habitats)
than on favorable estuarine conditions. Another behavioral difference between chum
salmon and species that rear extensively in freshwater is that chum salmon form schools.
Presumably, this behavior reduces predation (Pitcher 1986), especially if fish movements
are synchronized to swamp predators (Miller and Brannon 1982).
The duration of estuarine residence for chum salmon juveniles are known for only a few
estuaries. Observed residence times range from 4 to 32 days; with a period of about 24
days being the most common (Johnson, Grant et al. 1997). Juvenile salmonids rely on a
variety of non-main channel habitats that are critical to rearing. All listed salmonids use
shallow, low flow habitats at some point in their life cycle. Examples of off-channel
habitat include alcoves, channel edge sloughs, overflow channels, backwaters, terrace
tributaries, off-channel dredge ponds, and braids (Anderson 1999; Swift III 1979).
Status and Trends
Chum salmon have been threatened by overharvests in commercial and recreational
fisheries, adult and juvenile mortalities associated with hydropower systems, habitat
degradation from forestry and urban expansion, and shifts in climatic conditions that
changed patterns and intensity of precipitation.
Chum salmon, like the other salmon NMFS has listed, 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 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 or alter wetland and riparian
ecosystems. The above activities and features also introduce sediment, nutrients,
biocides, metals, and other pollutants into surface and ground water and degrade water
104