This article was published on: 09/19/22 11:43 AM
Above: A map of the network of 281 acoustic receivers researchers used in this project. Each circle represents a receiver. The circles that are filled in indicated receivers where detections occurred and are scaled according to the number of fish that were detected at each receiver.
Washington Department of Fish and Wildlife researchers wrapped up a project this summer that could have important implications for how fishery managers design future coastal steelhead fisheries and prioritize habitat restoration projects.
Initially launched in 2021, the project used acoustic and satellite tags — traditionally used for tracking wildlife like elk and wolves — to get a glimpse into the life of coastal steelhead as they had back out to sea.
Supported through a partnership with NOAA Fisheries and the University of Alaska Fairbanks, WDFW researchers used the project to learn more about the decline of repeat spawning in coastal steelhead over the past 30 years and better understand where, when, and for how long coastal steelhead are migrating through coastal rivers.
Unlike their cousins the Pacific salmon, anadromous rainbow trout commonly known as steelhead, are capable of having offspring many times over the course of their lives. In the context of widespread declines in abundance, fisheries managers have increasingly prioritized research on steelhead iteroparity because repeat spawners typically have higher productive capacity than first-time spawners.
The study included 37 female hatchery-origin steelhead and 49 wild-origin steelhead, collected and tagged at Forks Creek Hatchery as they migrated upstream in Forks Creek, a tributary of the Willapa River. Following tagging, WDFW staff released the wild fish upstream of the hatchery so they could migrate to wild spawning grounds and released the hatchery fish downstream of the hatchery after spawning them. Prior to release, WDFW staff collected and processed scales from each fish to determine their age and natal origin.
WDFW staff and colleagues placed a network of 281 acoustic receivers throughout the project area, indicated below, to better track steelhead migration and survival.
Of the wild fish tagged, 73.5% died on the spawning grounds. Of the wild fish that survived the spawning grounds, 23.1% reached the ocean. Of the tagged hatchery fish, 13.5 hatchery fish survived to reach the ocean.
Researchers also looked at velocity, or how fast the fish moved out to the ocean, as well as how much time steelhead spent in each area of their journey out to sea. As indicated below, this analysis did show that the fish that survived to reach the ocean, called ocean migrants, spent more time in each segment than those that didn’t. This suggests that using freshwater habitats, perhaps for feeding and post-spawn recovery, is an important factor for early survival.
The research also provided evidence that steelhead out-migrate through rivers at night, a finding that builds on previous literature.
WDFW staff shared the results of this research at the American Fisheries Society Conference in Spokane in summer 2022 and will also be presenting at the Wild Trout Symposium in West Yellowstone in fall 2022.
In the future, WDFW researchers want to build on this study with a focus on movement patterns relative to changes in stream temperature.