Two NOAA researchers are exploring uncharted territory to better understand the migratory behavior of Columbia River steelhead listed as threatened under the Endangered Species Act.
Last spring, NOAA Fisheries biologists Laurie Weitkamp and Michelle Wargo Rub (along with a team of researchers from Oregon State University and Pacific States Marine Fisheries Commission), implanted acoustic tags in 100 juvenile steelhead before releasing them back into the estuary at the mouth of the Columbia River. From there, the fish began their 1- to 2-year journey into the ocean.
“We know a lot about Columbia River’s chinook and coho salmon’s migration behavior, but very little is known about where steelhead go once they enter the ocean from the Columbia River,” said Weitkamp, who researches the estuarine and marine ecology of Pacific salmon, and the factors that affect their survival. Rub studies landscape ecology principles and spatial statistical methods to investigate pattern and scale in aquatic ecosystems.
Working with numerous collaborators on the shore and seas, Rub and Weikamp will try to track the fishes’ migration patterns using a variety of acoustic receivers. The receivers are placed on towed hydrophones, stationary arrays, and some even are mounted on elephant seals, which tend to cross paths with the salmon.
Researchers believe that an improved understanding of the steelhead’s ocean migration will reveal how ocean conditions might influence their growth and survival, and help biologists predict how steelhead might respond to climate change.
“What we do know is that they go far west into the North Pacific,” Weikamp said. “If you draw a line from Hawaii to the west side of the Aleutians, that’s about where we believe they’re headed. What we don’t know is if they all go there, and how long it takes. We have very little census information on them.”
The acoustic tags implanted in the steelhead give out a unique ping at – 69 kilohertz, she said.
The different listening arrays can hear the tags if the fish get within a half-kilometer of the hydrophones.
“We implanted as large a transmitter as feasible into the fish,” explained Rub. “By working with a low transmission rate, we get a longer battery life. Also, if we intercept the fish and put the tags in right before they hit the ocean, we maximize the time that the transmitters will be active while the fish are at sea – sometimes as long as nine to 10 months.
“However, sometimes steelhead will hang out for weeks in the estuary,” Rub said. “Although we can track them there too, time spent in the river eats up battery life for ocean tracking studies.”
There is a series of fixed lines of receivers along the west coast, called the Pacific Ocean Shelf Tracking Project array, which includes a line out on Willapa Bay with receivers that extends about 30 kilometers. “If our steelhead head north a little bit, they’ll be picked up there,” Weitkamp said.
One of the more interesting aspects of the study is using elephant seals to track steelhead migration behavior.
“The elephant seals also migrate and there’s a good chance that they will overlap with the steelhead,” Rub said. “It’s not inconceivable that both might be in the same area.”
“We also have some research ships listening for marine mammal calls, and they have receivers they can deploy, but it’s a bit of a shot in the dark,” Rub said. “They have heard other fish – not ours. Our hopes lie with the POST array and female elephant seals.”
Rub said that the elephant seals should be returning in December, and she hopes that they will find some detections on the seals’ receivers.
Both Weitkamp and Michelle Wargo Rub equated the effort to searching for a needle in a haystack. “Not to downplay this study, but it is a pilot project,” said Rub.
For more information about the study, go to: http://www.nwfsc.noaa.gov/features/steelhead_migration/steelhead-migration.cfm