Biological Opinions - Bureau of Reclamation

eproduction, and distribution. The fourth VSP parameter, diversity, relates to all three jeopardy
criteria. For example, numbers, reproduction, and distribution are all affected when genetic or
life history variability is lost or constrained, resulting in reduced population resilience to
environmental variation at local or landscape-level scales.
12.2 Status of the Species
In this section, NMFS develops a rangewide assessment of the condition of the species (i.e., its
status). NMFS describes the factors, such as life history, distribution, population sizes and
trends, and evidence of resiliency and redundancy, which help determine the likelihood of both
survival and recovery of the species. In doing so, NMFS describes how vulnerable the species is
to extinction.
NMFS listed the SONCC coho salmon ESU, which includes all naturally spawned populations of
coho salmon in coastal streams between Cape Blanco, Oregon in the north to Punta Gorda,
California in the south, as a threatened species in 1997 (62 FR 24588; May 6, 1997). In 2005,
NMFS reaffirmed its status as a threatened species and also listed three hatchery stocks as part of
the ESU (70 FR 37160; June 28, 2005). Analysis of recent genetic data from coho salmon in this
and adjacent ESUs (Oregon Coast ESU to the north and Central California Coast ESU to the
south) supports the existing boundaries of the SONCC coho salmon ESU boundary (Stout et al.
2010, Williams et al. 2011). NMFS recently completed a status review of the SONCC coho
salmon ESU (Ly and Ruddy 2011) and determined that the ESU, although trending in declining
abundance, should remain listed as threatened.
12.2.1 Life History
Coho salmon is an anadromous fish species that generally exhibits a relatively simple 3-year life
cycle. Adults typically begin their freshwater spawning migration in the late summer and fall,
spawn by mid-winter, and then die. Spawning occurs mainly in November and December in
small streams that flow directly into the ocean, or tributaries and headwater creeks of larger
rivers (Sandercock 1991, Moyle 2002). Depending on river temperatures, eggs incubate in
‘‘redds’’ (gravel nests excavated by spawning females) for 1.5 to 4 months before hatching as
‘‘alevins’’ (a larval life stage dependent on food stored in a yolk sac). Following yolk sac
absorption, alevins emerge from the gravel as young juveniles or ‘‘fry’’ and begin actively
feeding. Coho fry typically transition to the juvenile stage by about mid-June, and both stages
are collectively referred to as “young of the year.” Juvenile rearing usually occurs in tributary
streams with a gradient of 3 percent or less, although they may move up streams with as much as
five percent gradient (Agrawal et al 2005, Leidy et al. 2005). Juveniles have been found in
streams as small as 1 to 2 meters wide, and may spend 1 to 2 years rearing in freshwater (Bell
and Duffy 2007), or emigrate to an estuary shortly after emerging from spawning gravels
(Tschaplinski 1988). Coho salmon juveniles are also known to “redistribute” into non-natal
rearing streams, lakes, or ponds, often following rainstorms, where they continue to rear
(Peterson 1982). Juveniles rear in fresh water for up to 15 months, then migrate to the ocean as
‘smolts’ in the spring. Coho salmon typically spend about another 15 months in the ocean before
returning to their natal stream to spawn as 3 year-olds. Some precocious males, called ‘‘jacks,’’
return to spawn after only 6 months at sea.
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