Science Friday: Ephemeral Streams Provide Key Steelhead Habitat
Previously we wrote about the importance of ephemeral streams to steelhead. These are smaller waters, typically in headwaters and tributary drainages, segments of which dry back in summer or that flow intermittently. Today we pick up the topic again because of recent developments on the federal policy front that threaten these important habitat areas.
On July 27, the U.S. Environmental Protection Agency opened a 30-day period for public comment on the Trump administration’s repeal of the 2015 Clean Water Rule. This rule, adopted by EPA after years of scientific analysis and public feedback, affirmed that water quality protections under the landmark 1972 Clean Water Act applied not only to mainstem rivers and lakes but also to their sources: smaller creeks and wetlands which may be wet only seasonally. This interpretation was in effect for thirty years after the Clean Water Act was signed into law (it was called into question by two Supreme Court cases in the 2000s). Sportsmen’s groups such as Trout Unlimited strongly supported the Clean Water Rule, as cold, clean water is the most basic requisite for steelhead.
How do we know that ephemeral streams, which would lose federal water quality protections under Trump’s order, are vital for steelhead? A 1973 report to the Oregon State Game Commission by Fred Everest provides a solid scientific answer.
Everest et al examined the life history of wild summer steelhead in Oregon’s Rogue River. The study spanned four years from 1968 to 1971 and identified 93 tributaries of the Rogue and Applegate Rivers as important spawning areas. Most of these streams were small, with winter flows less than 50 cubic feet per second (cfs), and surprisingly only a handful maintained surface flow during the summer.
The majority of streams studied were estimated to support fewer than 500 spawning adults, but collectively they were producing a significant portion of the total population. Furthermore, a quarter of the population came from just six streams. Of these only two maintained flow during the summer, one of which had maximum summer temperatures over 80°F — too warm for salmonids to survive. In the other stream irrigation water was the primary source of summer flow and historically it was likely intermittent.
In such conditions, as streamflows drop to a trickle and temperatures climb in waters that otherwise are prime spawning and rearing habitat, juvenile steelhead must migrate to suitable habitat as fry. This is no small feat as O. mykiss fry are notoriously poor swimmers. In this study, the fry were only a few weeks old by the time many of the monitored streams went dry in mid-June. But the study’s findings indicate the fry were migrating successfully as habitat conditions changed seasonally.
Possibly the most amazing finding of this work was that one of the most productive streams for steelhead had a peak flood flow of only 128 cfs and was dry annually from August through October during the study period. Despite these habitat limitations, this stream had an estimated spawning population of 2,000 adults. Steelhead were not simply making a living by utilizing apparently marginal or even poor habitat, they were thriving in it.
This case study demonstrates one of many life history adaptations summer steelhead use to persist in river basins throughout the semi-arid West, where streamflows are highly variable: They make use of habitat throughout the watershed, moving to more suitable locations as conditions become less favorable in the sometimes tiny tributaries where they were born. Such tributaries are crucial as spawning and rearing habitat for many wild steelhead populations. But they won’t remain that productive if we don’t protect their water quality from being degraded from human influences such as mining waste and timber harvest.
It is much easier, and cheaper, to conserve steelhead life histories now than to try to recover them down the road. The Trump administration’s efforts to remove water quality protections from headwaters and smaller tributary streams are a direct and significant threat to wild steelhead conservation and fishing opportunity. Please take action here to remind the EPA that ephemeral streams are important for the iconic freshwater game fish of the Pacific Northwest, and that we won’t have clean water in our rivers, for steelhead or for drinking, if we have dirty water upstream.
Stand up for clean water: