[env-trinity] CBB: Salmon History: Centuries Ago Juveniles Entered Columbia Estuary Younger, Smaller Than Today’s Fish

[Sari Sommarstrom]

THE COLUMBIA BASIN BULLETIN:
Weekly Fish and Wildlife News   www.cbbulletin.com
May 20, 2011 -- Issue No. 576

* Salmon History: Centuries Ago Juveniles Entered 
Columbia Estuary Younger, Smaller Than Today’s Fish

Chinook salmon reared in the upper stretches of 
the Columbia River watershed 250 to 500 years ago 
used to leave their freshwater habitat and enter 
the estuary ­ and possibly even the Pacific Ocean 
­ when they were smaller and younger than most of 
their contemporary counterparts.

Researchers tracking the life history of salmon 
long before dams were built on the Columbia say 
the finding suggests that fisheries leaders may 
need to manage for a diversity of life histories.

Results of the research have been published in 
the Canadian Journal of Fisheries.

“The Columbia River estuary is an amazingly 
productive system and there clearly are 
advantages for fish to enter into that 
environment,” said Jessica Miller, an Oregon 
State University ecologist and lead author on the 
study. “Yet today fish remain in fresh water for 
a longer period of time ­ possibly because they 
must navigate past the dams, and because river 
flows during their ocean migration have been 
reduced with the development of the hydropower system.

“Chinook salmon have a more diverse portfolio 
than other salmon species, which may be one 
reason some of their populations are doing so 
well,” Miller added. “Managing the resource to 
retain that diversity seems like a logical strategy.”

“We know there are advantages for the salmon to 
reach a certain size before entering the ocean, 
especially in avoiding prey,” Miller noted. “But 
there may be long-term advantages to having 
individuals that migrate at a diversity of sizes.”

To learn more about ancient salmon runs, the 
researchers worked with the Confederated Tribes 
of the Colville in Washington, where they 
obtained the skeletal remains of salmon from a 
former archaeological site just downriver from 
Grand Coulee Dam. The fish, which the scientists 
dated to 250-500 years ago, were in an area of 
the Columbia River which is no longer accessible 
to migrating fish because of the dams.

One goal of the research was to see if fish that 
used to go upstream of Chief Joseph Dam ­ the 
farthest upriver that salmon and steelhead return 
­ had different characteristics than present-day 
fish. To do this, they looked at the bony 
structure within the salmon’s ears called an 
“otolith,” which accretes calcium carbonate and 
forms growth rings. By examining the growth rings 
and isotopes within otoliths, scientists can 
ascertain the age of a fish, where it lived and sometimes what it has eaten.

“It’s pretty amazing that we can look at the 
otolith of a 500-year-old fish and determine 
which river it likely originated in and at what 
size it entered marine waters,” said Miller, an 
assistant professor of fisheries and wildlife who 
works out of OSU’s Hatfield Marine Science Center in Newport.

They do this by analyzing the ratio of 
strontium-to-calcium isotopes in the otolith. A 
high ratio indicates a fish has been living in 
salt water, while a lower ratio suggests recent 
freshwater history. They also can examine two 
isotopes of strontium, which can provide information on the river of origin.

“We can also estimate where in the river system 
they were, because as you move east to west, the 
rocks get younger and the strontium values 
change,” Miller said. “In most cases, the 
isotopic signature is extraordinarily revealing.”

Miller also was lead author on another study, 
published in the Marine Ecology Progress Series, 
which examined diversity of fish runs in modern 
populations. Focusing on Central Valley 
(California) chinook salmon, the study determined 
that adult fish typically had begun their juvenile migration in two “pulses.”

A majority of adults had begun their seaward 
migration as larger juveniles (75 millimeters or 
longer), which typically leave rivers in 
mid-April to May. But the adult sample also 
contained fish that had begun their emigration as 
smaller fish (less than 55 mm). Though fewer in 
numbers, these smaller fish were still 
significant and typically left rivers in February and March.

“In the Central Valley, the vast majority of 
hatchery production is focused on larger 
juveniles, whereas most of the naturally produced 
fish appear to emigrate at a smaller size,” 
Miller said. “Similar to the variation in adult 
run timing ­ which may protect runs against 
catastrophic floods, drought or disease ­ 
variation in the timing of juvenile migration to 
the ocean may be important for long-term survival.”

Other researchers on the Canadian Journal of 
Fisheries study include Virginia Butler, Portland 
State University; Charles Simenstad, University 
of Washington; David Backus, Williams College; and Adam Kent, OSU.

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