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Findings from a little-known weir on Auke Creek

Warming trend tied to change in salmon run timing

Posted: October 18, 2012 - 11:01pm
Netted in the waters just beyond Auke Creek, a sculpin is pictured. Recent findings by David Tallmon, an associate professor of biology at the University of Alaska Southeast, show that sculpin can change color quickly or slowly depending on their background and needs. It's a costly effort, however, and Tallmon said those that change color often and rapidly have a higher mortality rate.   ABBY LOWELL / JUNEAU EMPIRE
ABBY LOWELL / JUNEAU EMPIRE
Netted in the waters just beyond Auke Creek, a sculpin is pictured. Recent findings by David Tallmon, an associate professor of biology at the University of Alaska Southeast, show that sculpin can change color quickly or slowly depending on their background and needs. It's a costly effort, however, and Tallmon said those that change color often and rapidly have a higher mortality rate.

One thing is for sure about the fish that migrate through the Auke Creek weir: they’re shifty.

That’s what David Tallmon, associate professor of biology at the University of Alaska Southeast, will touch on at this week’s Evening at Egan Lecture happening at 7 p.m. tonight in the Egan Lecture Hall at UAS.

But the data collected on the fish moving through the Auke Creek weir doesn’t show these fish as being devious or sneaky.

Instead, it shows they change — some literally in a matter of minutes — and over time to adapt to their surroundings and environment.

Take the sculpin, for example, which he said live in the creek.

“We found that they have this really amazing ability to change their color and they can do it relatively quickly,” he said. “They have a short term — on the order of minutes — and they have a longer term — over the course of weeks — ability to change their color and we found that under some circumstances, which we simulated in the lab, that ability can be costly.”

So costly, in fact, this ability increases their mortality or decreases their survival.

“(With) some of our treatments we actually shifted their background on them and they had to constantly try to adjust their bodies to match the background. So, at least under lab conditions, there is maybe a cost of a rapidly changing environment and having to adjust those those environments for sculpin.”

While this capability may be high-priced, it is also key to avoiding predation. In another experiment, Tallmon worked with one undergraduate student to conduct an experiment where model sculpin of varying colors were placed in the water against differing backgrounds.

“We found that those that contrasted more, got eaten more,” he said.

Yet sculpin make up a small percentage of the fish that swim in Auke Creek waters. Primarily, it’s salmon, cutthroat and dolly varden that rule the waters, so to speak.

Tallmon, who worked in collaboration with scientists from NOAA, UAS, UAF and with his own students, looked at trends in migration timing for those species of fish. He said he examined both migration from freshwater to the ocean, and from the ocean back.

“Essentially the bottom line is we found that looking across different species ... we found evidence of a compressed range of dates that adults are returning from the ocean,” he said. “And it looks like temperature (also) plays a role in changing their migration timing.”

In other words, from the first day that the fish begin to come in to the last day a fish arrives — that period of time is shrinking. For instance, in the 1970s, salmon migrated past the weir on the way to spawn over a 79 day period. Today, spawning salmon can be counted migrating past the weir, which has helped to facilitate this type of research for decades, only 55 days a year.

While their availability for humans and non-humans may be more limited today than in the past, the numbers of fish remain as strong as ever, Tallmon said.

He said this is an indication the fish have evolved and appear to be resilient to the environmental changes that have occurred over the last few decades.

Ultimately, he said, the trends he’s seeing on this little-known creek are of concern. But when it comes to predicting how these fish will fare in the future, he’s quick not to draw any conclusions.

“It’s hard to say (what will happen),” he said. “The abundance is stable. That’s the reassuring part.”

• Contact Outdoors Editor Abby Lowell at abby.lowell@juneauempire.com.

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