Our new Biological Assessment is out - Klamath Basin Crisis

Klamath Project Operations Biological Assessment
Coho Salmon: Coho Salmon Life History, Abundance, and Trends
Fry Colonization (March through June)
Upon emergence, coho salmon fry move quickly to
slow velocity habitats, typically along the channel
margin, or they continue to move downstream.
They have a strong affinity for very slow velocity
water and generally move there as rapidly as
possible. Fish that emerge during high flows can be
swept downstream, moving them to less suitable
habitats, increasing bioenergetics costs, and
increasing predation exposure. Survival during the
fry colonization stage is mostly density-independent
because of their small space requirements.
Coho Salmon Fry
A fry is a young salmon that is freeswimming
and feeding. The vertical
stripes and bars (parr marks) found on
the sides of juvenile salmon assists to
camouflage them from predators.
Juvenile Rearing (July through February)
Juvenile coho salmon, referred to as parr, are found residing in a wide variety of
stream sizes and types during summer. They are typically found in the highest
densities within their natal streams.
Survival of juvenile coho salmon during summer can be strongly densitydependent
in smaller streams. Competition for shrinking space, due to declining
flows in late summer, as well as limited food, results in reduced survival at higher
juvenile abundance. Juvenile coho salmon preference for slow velocity water
remains strong during this life stage, where they are most often found in pools.
The highest densities are generally found in the pools of the smallest streams.
In large rivers, side channels, off-channel, and channel edge habitats provide
important rearing areas for juvenile coho salmon (Beechie et al. 2005). Usually,
groundwater channels are used almost exclusively by coho salmon and can be
very productive for the species. Rivers and streams with high nutrients and
abundant food resources can provide exceptional rearing conditions and increased
carrying capacity from an energetic standpoint. Conversely, high water
temperatures during the summer can be a limiting factor affecting the distribution,
growth, and survival of juvenile coho salmon.
Summer — Thermal Refugia
Animals react not only to immediate changes in their environment but also to cues
that signal long-term changes in their environment that prompt adaptation in order
to survive. Members of the salmonid family are cold-blooded organisms that can
respond to an uncomfortable water temperature by moving from one spot to
another to maintain thermal comfort. If the reason they move is because of a
discrepancy between the temperature of the surrounding water and a “set point” in
their brains that registers thermal comfort, their response is known as behavioral
thermoregulation.
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