More than a decade since dam removal on the Elwha River, the bug communities in the river’s estuary appear to be rebounding to pre-project levels with critters like worms and flies providing significant food sources for juvenile salmon.
Removal of two fish-blocking dams between 2011-2014 unleashed millions of cubic yards of sediment from the river’s former reservoirs, much of it flowing downstream and expanding the river’s delta and creating new habitat.
“While major changes to the estuary would have happened during dam removal, current invertebrates are living through regular sediment deposit activity, now that it’s in a more normal range,” said Justin Stapleton, a project biologist for the Lower Elwha Klallam Tribe. “We find a lot of chironomids (a family of two-winged flies) and oligochaetes (the earthworm subclass).”
“The diversity of insects also may continue to increase over time as the vegetation grows in and around the newly expanded estuary,” said Matt Beirne, the tribe’s natural resources director.
To monitor those changes, the tribe has been studying the bugs in the estuary and the salmon that eat them since 2007—before, during and after dam removal.
The tribe collects fish from the estuary and pumps their stomachs to see what they’re eating. The tribe also takes sediment samples to look for insects and other macroinvertebrates, and compares the sediment samples to the stomach samples.
“The diet study is a complement to the sediment work, which enables us to evaluate possible effects of dam removal impacts on the juvenile salmon diet,” Beirne said.
While the 2023 data is still being analyzed, the tribe, National Oceanic and Atmospheric Administration, U.S. Fish and Wildlife Service and U.S. Geological Survey examined samples collected in 2007 and 2013, and found the influx of fine sediment and cloudiness in the river following dam removal temporarily diminished the availability of food for fish.
Many insect species disappeared briefly during this period but juvenile salmonids appeared to change the way they foraged by eating more terrestrial types of invertebrates in the river, or other species like plankton and stickleback fry in the estuary, so the amount of energy in their diets stayed the same, Beirne said.
Eventually, this year’s data will be analyzed with 2007, 2013 and 2017 data to reveal even more connections between the sediment, salmon and bugs of the evolving Elwha watershed, Beirne said.
The stomach contents of a juvenile chinook are sampled for analysis of what salmon are eating in the Elwha River estuary. Story and photos: Tiffany Royal