CORVALLIS, Ore. – While many people along Oregon’s North Coast are home sound asleep researchers from the Oregon Department of Fish and Wildlife will be working late to unlock clues about returning chinook salmon.
Starting this month, ODFW survey teams will be collecting adult chinook that have returned to the Nehalem and Nestucca rivers in order to gain a better understanding of how many salmon survive the arduous round trip from the North Coast to Alaska and back.
Teams working from shore and in boats will use drift nets to catch, mark and release as many chinook as possible. The study is expected to begin by the middle of the month and take place annually from August through October for the next 4-5 years.
Much of the work will happen at night to avoid conflicts with anglers and reduce stress on fish, according to Shelly Miller, project leader stationed at ODFW’s Corvallis Research Lab. In addition, researchers believe working during the wee hours will improve their catch rates and produce more data from which to draw conclusions.
“More fish move at night,” Miller said.
Crews use a number of techniques to reduce stress to the fish, including not handling the fish at all if water temperatures are above about 64 degrees Farenheit.
The project leader explained that returning chinook will be collected near the mouths of the two rivers, marked and released to continue their migration to upstream spawning grounds. When those fish are examined a second time during spawning surveys or after being caught on anglers’ rods, the totals will be compared to the number of unmarked chinook to develop a population estimate. No live fish will be handled during the spawning surveys. Only carcasses will be examined for marks.
“This is a common technique for estimating animal populations,” Miller said.
Researchers will supplement their data by conducting angler creel surveys during the daylight hours, counting spawning sites or “redds” when fish are actively spawning and by counting and examining carcasses from the river bottoms after the salmon have completed their life cycles.
Population estimates developed through this research will be used in local management decisions and in broader discussions about salmon under the Pacific Salmon Treaty, according to Chris Knutsen, district fish biologist for ODFW’s North Coast Watershed.