The Lower Elwha Klallam Tribe, in cooperation with Washington Department of Fish and Wildlife and Olympic National Park, is determining how many hatchery-origin and natural-origin chinook salmon are returning to the Elwha River since two fish-blocking dams were removed.
The tribe and partners have been counting returning chinook adults from summer through early fall, and surveying chinook redds (egg nests) and collecting ear bones from salmon carcasses in mid-to-late September.
When an ear bone, or otolith, is removed from a carcass and placed under a microscope at the state’s lab, scientists look for a mark on the bone that indicates it’s a hatchery fish.
“When the fish are in the state hatchery, the water temperature is held at a certain degree for a certain period of time, resulting in marking a ring on the ear bone, which can be seen as a growth ring, like on a tree,” said Mike McHenry, the tribe’s habitat program manager.
“We used an otolith mark to indicate hatchery origin, rather than the standard adipose fin clip, in order to reduce mortality in mark-selective fisheries and maximize the number returning to recolonize habitat the Elwha River,” said Joe Anderson, a WDFW research scientist.
The tribe also uses a sonar system in the lower river to determine how many fish are returning between June and September. However, the sonar can’t decipher the type of fish, so the tribe nets the river at the same time to identify fish, then correlates the net data with the sonar data.
“We have seen a dip in the numbers of returning adult chinook over the last two years – about 2,500 fish compared to the previous three years of about 4,500,” said Keith Denton, a consultant overseeing the tribe’s sonar program. “This is most likely caused by the fact that returning adults from the last two years were juveniles in the river four and five years ago, and experienced the brunt of the sediment impacts from dam removal during a delicate part of their life.”
Nevertheless, the number of adults returning the past two years is still about equal to the 20-year average, Denton said, and the fish seemed to have dealt with any short-term negative impacts from dam removal remarkably well.
The late summer chinook redd surveys assess where fish are going in the watershed.
“Chinook are showing good signs already,” McHenry said. “They want to move upstream and have occupied natural habitat on their own.”
While salmon spawning in the river during dam removal from 2013-2015 didn’t fare as well because of the drastically changing river, there was an uptick in the out-migration of natural chinook smolts in 2017, McHenry said.
“I expect when those fish return as 3-, 4- and 5-year-olds, we’ll see the contribution of natural-origin chinook increase,” he said, “But for now, basically, 90 percent of the returning chinook adults are still hatchery-origin.”
Otoliths (salmon ear bones) are sampled from spawned out chinook salmon carcasses on the river and its tributaries. The otoliths are later studied under a microscope to determine if a fish is of hatchery origin or natural origin by looking for a special mark on the bone, much like a tree’s growth rings. Photo: T. Royal