What’s in a weir
A new weir on the South Fork Toutle River contributes to fish management in Southwest Washington
Beginning this week, visitors to Harry Gardner Park in Cowlitz County may see a new feature alongside the playground equipment and hiking trails: A weir stretching across the South Fork Toutle River.
The weir is being installed to help manage the return of hatchery fish moving further up the South Fork Toutle, toward Mount Saint Helens and fall Chinook salmon spawning grounds.
There are couple of important things to be aware of if you’re recreating near the new weir. First, obey all posted signs — trespassing on or around the weir is not only dangerous, it’s also illegal. Second, fishing is prohibited within 400 feet downstream and 200 feet upstream of the weir (see WAC 220–305–090 for additional information).
The weir on the South Fork Toutle won’t be the first in the region; it joins seven others that have been operating across southwest Washington for more than a decade. But despite their history and presence in watersheds throughout Washington, many misconceptions remain about what weirs are and what they do.
The weirs of southwest Washington
Some believe that a weir is simply a barrier that stretches across a river similar to a dam, but typically with a lower profile that allows water to pass through without allowing fish to pass through. It’s true that there are weirs that are used to influence the flow and level of a waterbody, but WDFW uses “resistance board” weirs to instead manage the passage of fish traveling up a river. These weirs feature a trap that the fish swim into where they can be sorted, removed if necessary, and tagged by WDFW staff for monitoring purposes.
The South Fork Toutle weir will allow fishery managers to reduce the number of “hatchery-origin” — fish reared in hatcheries — Chinook salmon making their way to the upstream spawning grounds, reducing competition with natural-origin, or “wild,” fish. It will remain in the river until late October, long enough to intercept the fall Chinook runs.
Many of the existing weirs already in operation throughout the region serve a similar function, deployed in a similar late-summer to fall timeframe.
You can find a breakdown of which weirs are in the water, and when, at WDFW’s southwest Washington fishing reports webpage.
At all of these locations, natural-origin fish and any other salmon and steelhead species are typically allowed to continue upstream to spawn. This is an important requirement of the Endangered Species Act (ESA), which requires WDFW and co-managers to manage the proportion of hatchery-origin spawners (pHOS) returning to the spawning grounds. Under the Mitchell Act, these weir operations are required to maintain current production levels at affected hatcheries.
In certain cases, some of the wild fish are collected to help meet broodstock goals at nearby hatcheries, such as fall Chinook intercepted at the Washougal and the Green River weir.
All of the wild fish intercepted at the new South Fork Toutle weir will be released to continue their journey upstream.
In addition to promoting conservation of wild salmon populations, a 2019 report on a half-decade of weir operations in southwest Washington noted that weirs contribute to existing salmon-monitoring efforts and assist in collection of broodstock for use in hatcheries. All of the managed hatchery fish collected at southwest Washington weirs are either surplused — that is, collected for donation to local foodbanks, placed back in the river for nutrient enhancement purposes, or removed a under a previously established statewide contract — or collected for broodstock.
The truth about weirs
Though weirs have been in use for decades for fish management reasons, some still wonder about the role weirs play in larger fishery management.
Some question the weirs’ efficiency in terms of reducing the number hatchery fish on the spawning grounds. The truth is, weirs can be highly efficient at removing fish, but the effectiveness of each individual weir varies widely based on things like the weir’s location in the river, the numbers of returning fish in a given year, and even the weather.
“At the end of the day, these weirs operate in the real world, with all the complications and considerations that come along with that,” said Elise Olk, a southwest Washington fish biologist and one of the authors of the 2019 study. “Even something as simple as a week of rain and high river flows can affect the number of fish passing over a weir, changing the makeup of the spawning grounds for that year.”
Another common concern is that because many salmon fisheries throughout Washington target hatchery-origin fish and anglers must release wild fish, these weirs “steal” fish from fisheries by reducing the numbers of hatchery salmon available for harvest above the weir.
It’s true that the number of hatchery fish can be significantly reduced upstream of areas where weirs are in operation, but hatchery fish may still get above the weirs to spawn during high flow events when the weir is not 100 percent effective. In areas open for hatchery salmon fishing, anglers are encouraged to help further reduce the number that reach the spawning grounds.
“We recognize that these weirs can’t remove every fish, but because they cover the entire river, they’re more efficient than even the most robust fishery at removing hatchery spawners,” Olk said. “We are constantly working to balance conservation with fishing opportunity, and we recognize that these weirs can reduce upstream fishing opportunity. But we are required to conduct these operations under the Mitchell Act for conservation and to continue hatchery production in the region.”
The truth about weirs is that they’re intended to promote recovery of wild salmon populations, with the expectation that recovery will eventually lead to increased harvest opportunities, and are a valuable tool for collecting information about those populations while also promoting conservation and opportunity.
