Science Friday: Steelhead in hot water, and what it means for catch-and-release
As predicted for summer steelhead in the Columbia River and many other watersheds in Washington and Oregon, something has happened to the fish. There are precious few of them this season. But it’s important to remember that ebb and flow in population size is part-and-parcel with these fish — and for all salmon in general.
We likely pay more attention to these shifts in run size now because we have such rapid access to scientific data and analysis and are more informed than ever before. We can go online and find preseason run forecasts, check dam counts and peruse social media for up-to-date fishing reports. Not much happens, or is forecast to happen, without a wide swath of anglers becoming aware of it.
Especially in years like this, now that summer has settled in, elevating temperatures and reducing flows, it is appropriate to think more about how we manage ourselves as anglers to minimize our impacts on the fish. Water temps are now creeping past the 70°F mark in many streams, and getting warmer. Those temps in and of themselves are not a huge problem for steelhead, but they can become problematic for catch-and-release angling.
A study by Taylor and Barnhart out of the California Cooperative Fishery Research Unit looked at C&R mortality of adult steelhead in relation to water temperature. The research team caught 126 summer runs in water temperatures ranging from 46°F to 77°F from July-October in 1995 and 1996. All the steelhead were caught on lures.
What did they find? Several important results. First, they had only twelve mortalities (9.5 percent).
Second, of those mortalities, ten occurred when water temperatures were 70° (21°C) or higher. So, most mortalities happened when temperatures were pretty warm.
Third, they used their data to develop a model that predicted C&R mortality as a function of water temperature. See Figure 5 from their report. That model indicated that mortality dramatically increased as temperatures increased above 70°F, from about 10 percent at 70°F to about 22 percent at 73.4°F. At the extreme end, the mortality rate was 43 percent at 75°F, but only 5 percent when water temperatures were less than 68°F.
The results should not be surprising. Studies on other species have found similar results. Research on Lahontan Cutthroat trout found that mortality was less than 1.5 percent when water temps were less than 60°F, but increased to almost 50% when temperatures exceeded 68°F. A study on Atlantic salmon found that the mortality was 40 percent when fish were caught at temperatures of 71.5°F and higher.
It’s pretty clear that elevated water temperatures and angling don’t mix well if the goal is to maximize survival of adult steelhead after C&R. Such mortality rates are an important consideration, especially when run sizes are low. Thousands of anglers are fishing for summer steelhead across Oregon, Washington, Idaho and California. Think about the potential impacts if we all were to continue fishing when water temperatures exceed 70°F.
What’s a poor steelhead-crazed angler to do in times like this? There is no easy answer. So-called “Hoot owl” closures are a good idea (and in fact may be required) for some waters, especially during heat waves. Carry a thermometer and use it. In summer, we all must take extra precautions to be aware of water temperatures and make sure our handling of steelhead is impeccable (#Keepemwet).
We don’t know what the future holds. The only thing we can control as anglers is ourselves, and one way to minimize our impacts this year is to avoid fishing once temperatures start reaching that “death zone” for steelhead.