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

Of the Pacific salmon species, Chinook salmon exhibit one of the most diverse and
complex life history strategies. Chinook salmon are generally described as one of two
races, within which there is substantial variation. One form, the “stream-type” resides in
freshwater for a year or more following emergence from gravel nests. Another form, the
“ocean-type” migrates to the ocean within their first year. The ocean-type typifies
populations north of 56ºN (Healey 1991). Within each race, there is often variation in
age at seaward migration, age of maturity, timing of spawning migrations, male
precocity, and female fecundity.
Status and Trends
Over the past few decades, the size and distribution of Chinook salmon populations have
declined because of natural phenomena and human activity. Geographic features, such as
waterfalls, pose natural barriers to salmon migrating to spawning habitat. Flooding can
eliminate salmon runs and significantly alter large regions of salmon habitat. However,
these threats are not considered as serious as several anthropogenic threats. Of the
various natural phenomena that affect most populations of Pacific salmon, changes in
ocean productivity are generally considered most important. Natural variations in
freshwater and marine environments have substantial effects on the abundance of salmon
populations.
Salmon along the U.S. west coast are prey for a variety of predators, including marine
mammals, birds, sharks, and other fishes. In general, Chinook salmon are prey for
pelagic fishes, birds, and marine mammals, including harbor seals, sea lions, and killer
whales. Chinook salmon are also exposed to high rates of natural predation, during
freshwater rearing and migration stages, as well as during ocean migration. 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 ESUs. Human
activities include the operation of hydropower systems, over-harvest, hatcheries, and
habitat degradation including poor water quality from chemical contamination.
60