Potholes Terns Like Upper Columbia Steelie, Springer Smolts

Betcha a buck that Sammie the Salmon ends up as fish dinner for a tern on Potholes Reservoir.

Sammie is a spring Chinook that was released on Monday night from the Winthrop National Fish Hatchery on the upper Methow. So far she’s made it to the Columbia and down through Wells Dam — the U.S. Fish and Wildlife Service created a Google Map to track her progress — but the colony of Caspian terns on Goose Island have a taste for young spring Chinook from these parts.

The birds fly the 30 or so miles from Potholes to the river to annually eat 3.6 percent of the spring smolt run, a percentage “significantly higher than all other Chinook stocks available to this colony,” according to a half-decade-long study of what certain birds eat along the Columbia and Snake Rivers.

That was over just two years of record, but the same flock also likes Upper Columbia steelhead, eating 10.0 percent of the summer-run smolts coming downriver. And a colony on Crescent Island south of Tri-Cities ate 7.7 percent of those coming down the Snake.

“That has been a shocker to us,” Oregon State University’s Dan Roby told the Columbia Basin Bulletin in a story out today. “It looks like the primary reason for going there is to work on salmonids, and in particular steelhead.”

It’s a worry because numerous stocks of Columbia Basin salmonids are listed as threatened under the Endangered Species Act.

The executive summary of the study — done by Bird Research Northwest for the Army Corps of Engineers — suggests that “the greatest potential for increasing survival of smolts from ESA-listed salmonid stocks by managing inland avian predators would be realized by focusing management efforts on Caspian terns nesting at colonies on Crescent Island, Goose Island, and the Blalock Islands. Reductions in the size of these tern colonies would enhance survival of upper Columbia River and Snake River steelhead stocks in particular.”

Blalock Islands are below McNary Dam.

The overall study looked at nine flocks and numerous other listed salmonid runs and concludes:

This system-wide evaluation of avian predation indicated that, among the nine piscivorous waterbird colonies investigated, Caspian terns and double-crested cormorants nesting on East Sand Island in the Columbia River estuary were consuming the highest proportions of available PIT-tagged smolts, with combined losses ranging from a low of 2.6% for Willamette spring Chinook to a high of 18.2% for Snake River summer steelhead during 2004-2009. Estimated predation rates associated with the tern and cormorant colonies in the estuary were generally 2-5 times greater than for inland bird colonies. Due to the relatively high observed predation rates in the estuary, and because all anadromous salmonids must migrate through the estuary, our results indicate that the management of terns and cormorants nesting on East Sand Island near the mouth of the Columbia River has the greatest potential to enhance survival of juvenile salmonids from all Columbia Basin stocks combined.

Interestingly, ESA-listed game fish aren’t the only species getting eaten. When researchers poked around the Snake from Clarkston down over three winters to see if double-crested cormorants were impacting listed fall Chinook, they found that the birds primarily chew on a whole lot of bass and panfish.

“The most prevalent prey types in the foregut samples were centrarchids (sunfishes and bass; 34.3% by mass), followed by shad (15.0%), cyprinids (11.7%), and salmonids (11.7%). Fall Chinook salmon comprised an average of 3.4% by mass of the cormorant diet,” says the study.

Smallies and panfish made up 66.7 percent of their diet in October but by December they depended on shad for 59.1 percent of their diet. Salmon and steelhead were most prevalent in November when they comprised 24.2 percent of foregut content.

For your Easter Weekend reading enjoyment, the entire 239-page study can be downloaded here.


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s

%d bloggers like this: