[env-trinity] PNW study: Understanding the Shapeshifting Rainbow Trout/Steelhead

[Sari Sommarstrom]

http://www.fs.fed.us/pnw/sciencef/scifi177.pdf

 

USFS-Pacific Northwest Research Station

SCIENCE FINDINGS - issue no. 177, Sept. 2015

 

IN SUMMARY

Steelhead are the sea-going form of Oncorhynchus mykiss. Rainbow trout, 

also O. mykiss, remain in freshwater. Each form, or life-history, can
produce 

offspring of the other, but the mechanism for this and potential effects
that 

climate change may have on the species are poorly understood. 

 

Forest Service scientist Gordie Reeves, along with colleagues from other
federal 

agencies and Oregon State University, conducted a series of studies to
better 

document the biological processes that affect the life-history expression of

O. mykiss. They found that standard metabolic rate and lipid levels play 

important roles: those fish with higher metabolisms and lower lipid levels 

tended to be steelhead, while those with lower metabolisms and higher lipid 

levels tended to be resident rainbows. Reeves' findings challenge the
existing 

theory that faster growing individuals of the species tend to be seagoing
steel-

head.

 

The research examined the effects of water temperature on life-history
expres-

sion within the species. These findings offer clues about how climate change


may affect the rainbow/steelhead ratio in the years ahead. This research
informs 

habitat improvement efforts and protection for steelhead populations, which
are 

listed under the Endangered Species Act. It provides context, revealing how
their 

life-history is interconnected with that of rainbow trout, which are not
listed.

 

More.

.Reeves cautions that it's a mistake to look at life-history strategies as a
black-or-white, 

either/or proposition. "Within the O. mykiss population, there are actually
multiple strate-

gies to achieving reproductive success," he says. "Think of the population
as essentially 

trying to diversify its portfolio of strategies to ensure that the species
as a whole is main-

tained."

 

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