Prioritizing habitat restoration work will become more important, more so than cherry picking available projects, in the years ahead as managers of native fish stocks such as spring chinook salmon try to ward off the effects of climate warming.
For example, river warming will expand the territory of predatory non-native stocks like smallmouth bass, and thus increase the pressure on struggling populations of salmon and steelhead, according to ongoing research led by the University of Washington’s School of Aquatic and Fishery Sciences.
The research, funded by the U.S. Environmental Protection Agency, has from 2009-2013 focused on the Middle and North forks of the John Day River in north-central Oregon.
The John Day, approximately 281 miles long, is undammed along its entire length.
The tributary to the Columbia River is the third longest free-flowing river in the conterminous United States. It is home to naturally produced populations of steelhead, a stock listed under the Endangered Species Act, and chinook salmon.
The latest research manuscript, now titled “The interactive effects of climate change, riparian management, and a non-native predator on stream-rearing salmon,” has been accepted for publication in the Ecological Applications, a research journal of the Ecological Society of America.
The study examines current and projected conditions in the two forks, which have different histories and conditions.
“… additional warming in the MFJDR (a river system that is currently considered thermally impaired due to riparian vegetation removal) may result in the extirpation of the chinook salmon unless riparian restoration is undertaken to increase shade and offset the impacts of climate change,” the manuscript says.
The Middle Fork riparian zone has been degraded in many respects as the result of cattle grazing.
“This outcome is starkly different from that projected for the NFJDR where a relatively intact riparian corridor supports cool water habitat, even in the face of climate-induced stream warming.”
“We intersected downscaled global climate forecasts with a local-scale water temperature model to predict mid- and end-of-century temperatures in streams in the Columbia River basin; we compared one stream that is thermally impaired due to the loss of riparian vegetation and another that is cooler and has a largely intact riparian corridor,” the new research report says.
“Using the forecasted stream temperatures in conjunction with fish-habitat models, we predicted how stream-rearing chinook salmon and bass distributions would change as each stream warmed. In the highly modified stream, end-of-century warming may cause near total loss of chinook salmon rearing habitat and a complete invasion of the upper watershed by bass.
“In the less modified stream, bass were thermally restricted from the upstream-most areas. In both systems, temperature increases resulted in higher predicted spatial overlap between stream-rearing chinook salmon and potentially predatory bass in the early summer (2-4-fold increase) and greater abundance of bass. We found that riparian restoration could prevent the extirpation of chinook salmon from the more altered stream, and could also restrict bass from occupying the upper 31 km of salmon rearing habitat.”
According to Dave Lawrence, a UW graduate student who served as lead author for the new research paper, warm conditions in the John Day basin have enabled the spread of non-native smallmouth bass.
The bass were believed to have been introduced to the river in 1971 and are now present throughout the lower 180 miles of the system.
And the warmwater fish are expanding their range, sharing more and more of the river with coldwater-loving salmon. The bass now provide a “blue ribbon” fishery for anglers, Lawrence says.
“What we did not know until this study, is just how far upstream bass have moved from their initial introduction site,” Lawrence said in a recent update letter sent to landowners along the John Day that had allowed river access to the researchers. “By conducting extensive snorkel surveys in 2009 and 2010, we found that bass have moved 50-75 miles upstream, depending on if you consider Service Creek or Monument to be the site where they were initially introduced.
“Bass now currently co-occur with juvenile chinook salmon that reside and grow in the North Fork and Middle Fork of the John Day River during their first summer, before they outmigrate as smolts the following spring,” the letter says. “This is the first study to describe the co-occurrence of these species, and it has broad implications, given the predatory nature of smallmouth bass.
“In our studies we also determined that the upstream extent of bass in the John Day River is governed by water temperature. If water temperatures are too cold, young-of-year bass are not likely to grow large enough their first summer to survive the winter. Bass stop feeding in the winter and therefore must live off whatever energy reserves they established during the summer, and the smaller the bass, the smaller their energy reserve.”
Lawence said that one goal of the research was to develop forecasts regarding how far upstream bass are likely to move if climate change increases stream temperatures.
“The most up-to-date climate change predictions suggest that water temperatures in the North Fork and Middle Fork John Day River will increase 3.6-5.4 degrees F by 2080. Given that degree of change, our models suggest bass are likely to occupy the entire Middle Fork, all the way up to headwaters, by 2080 (representing a 35 mile gain in upstream extent). In the cooler North Fork John Day River, bass are likely to gain an additional 22 miles of upstream habitat.”
The researchers also say that juvenile chinook are ill-equipped to defend themselves against the newly arrived predator population. The chinook appear to have adapted over time to recognize predators such as the northern pikeminnnow.
“… if they ‘smell’ pikeminnow, they either disperse or hide. Fish commonly use smell (Le., olfactory) cues to anticipate the presence of a predator,” Lawrence’s letter says.
“Bass, on the other hand, are novel to juvenile chinook salmon. What we found is that juvenile chinook salmon do not behaviorally respond to the presence of bass, making them much more susceptible bass predation.
“Overall, we have had some pretty interesting discoveries in the John Day River basin, and the results from this work are likely to apply to many other Pacific Northwest river systems where bass are established.”
“The interactive effects of climate-change, riparian land-use, and introduced species will determine the future of rearing salmon populations,” the draft manuscript says. “This work highlights the potential for restoration to mitigate some of the effects of climate change, especially in systems with a high degree of current riparian vegetation alteration and spreading non-native species.”
See the website below for the most up-to-date updates on the UW research group's work:
For related information see:
-- CBB, May 31, 2013, “Study: Climate Change Threatens Extinction In Next 100 Years For 82 Percent California Native Fish” http://www.cbbulletin.com/426813.aspx
-- CBB, May 3, 2013, “Bassmaster Magazine Again Brags On Dworshak, Columbia River As Some Of Country’s ‘Best Bass Lakes’’’ http://www.cbbulletin.com/426417.aspx