MCKENZIE BRIDGE, Oregon (STPNS) -- Results of a study of stocks of wild steelhead in two nearby streams show the potential for young salmonids to adapt to warmer water temperature, according to recent research.

The study has implications for a range of Pacific Northwest rivers and offers some hope that salmonid populations will adapt and survive, at least within a limited temperature range.

The study focused on two distinct stocks of steelhead from the Duckabush and Dewatto rivers. Both flow into Hood Canal within 50 miles of each other. The Duckabush flows from the Olympic Mountains and has cooler overall temperatures during steelhead rearing than the Dewatto River, which is fed by springs and rainfall and flows from the east at a lower elevation.



“Our work provides evidence that these two populations ex-press differences in key life history traits and that these traits are influenced by both genetics and temperature,” said Katy Doc-tor, research fishery biolo-gist and contractor from Ocean Associates, Inc. working with NOAA Fisheries. “It certainly lends support that among other populations of salmonids, we might also see variable plasticity in important life history traits if exposed to different temperatures than their natal environment.”

According to the study, this type of ability to adapt to local conditions, such as temperature, is a characteristic “fundamental to the evolution and persistence of populations” and is crucial to maintaining diversity. It may also be crucial to surviving warming temperatures.

The article was published this month in Transactions of the American Fisheries Society and describes work completed in mid-2013 by NOAA Fisheries’ Northwest Fisheries Science Center.

Traits investigated in the study - growth, smoltification, male maturation at age one in the two populations of steelhead - are a product of both genetics and their particular river environments, according to Doctor. Other studies have established the importance of genetics over growth, but this research establishes the impact of the environment, specifically temperature, on growth.

Studying the two naturally spawning distinct stocks of steelhead, the team of researchers collected eyed embryos from redds in each river from February to June of 2010. They reared the embryos at U.S. Fish & Wildlife’s Quilcene National Fish Hatchery. Signifying the difference between the rivers, the researchers collected embryos in the warmer Dewatto River about one month sooner than collection could begin in the Duckabush River.

After the embryos hatched and the fish began feeding, they were divided into batches and reared in eight separate tanks. Two batches of the Duckabush River embryos were reared in water temperatures mimicking what the fish would experience in the river and two batches were reared in water temperatures reflecting the warmer water of the Dewatto River.

Similarly for the Dewatto River embryos, two batches were reared in water temperatures indicative of the river and the other batches in the cooler water of the Duckabush River.

In this research setting, the researchers found that the Duckabush River steelhead produced fewer age-1 smolts by June than the Dewatto River steelhead and that most of those were produced from batches of the Dewatto River temperature environment where water was warmer. This shows that water temperature does have an impact on how quickly the fish reach maturity.

When placed in the Duckabush River temperature environment, the Dewatto River steelhead reached maturity slower than when they were reared in their own river environment.

“Interestingly, the Duckabush population seems to have inherently more plasticity (at least in growth rate, which regulates the other life history traits investigated) than the Dewatto population,” Doctor said. “This means that they are better able to take advantage of warmer temperatures to increase growth.”

This study provides proof that, within the temperatures tested, steelhead are able to adapt in these important life history traits, which could buffer against warming climates and allow them to adapt to warming temperatures (over an appropriate time frame), she concluded.

There likely are limits to how warm water can be and still provide a healthy environment for salmonids. The temperatures tested in this study were within optimal growing temperatures for these steelhead and they were not tested at the higher temperatures that, according to Doctor, could result in decline.

“And depending on the trajectory of changing river temperatures due to climate change, and the complex interactions between salmonids and their environment at different life stages, their fitness (survival) may increase or decrease,” she said. “Faster growth doesn’t necessarily equate to higher survival. Conserving the genetic diversity among and within steelhead populations is vitally important for future resilience of populations in the face of changing temperatures.