Aufeis may mark Grayling safe spots

Arctic Grayling Heidi Golden
This Arctic grayling from the Kuparuk Upper Spring pool displays iridescent purplish-pink scales and fin stripes typical of Kuparuk River grayling / Image Heidi Golden

“Who’s eating our fish?!” Heidi Golden posed in her journalistic record of Arctic Research and Exploration studying Arctic grayling. “From the snow tracks we saw, it’s most likely a fox. Other predators in this area might include, birds, wolverine, ermine and wolves.”

partially eaten Arctic grayling fish
Who’s eating the Arctic grayling? / Image Heidi Golden

Golden is an aquatic ecologist and a Ph.D. candidate in the University of Connecticut, Ecology and Evolutionary Biology Department. She came to Alaska to study Arctic grayling (Thymallus arcticus), especially a population of migratory grayling, which range along the Kuparuk River and its tributaries on Alaska’s North Slope. “They are a very important species,” an integral part of the ecosystem, Golden explained. “They are the only fish species in a lot of these tundra streams likely because of the harshness of the environment.”

A changing landscape

The Arctic grayling population which calls the upper Kuparuk River home relies on extensive migration; they might travel as far as 100 miles [160 kilometers] annually. Every year they spawn and feed while ranging in the river network. As the cold season sets in, Alaska river ice freezes from the top down. The fish forge back upstream to Green Cabin Lake to overwinter. Before the waterways are frozen solid they must reach the safety of the sheltering lake where deep waters remain liquid throughout the winter under a ceiling of thick ice.

These Arctic grayling need cold, clean water, and rely on multiple interlinked habitats to survive. This is a species living in an extreme environment. Golden’s work examines factors influencing Arctic grayling population dynamics. How do grayling respond when their aquatic habitats– specific to spawning, feeding, and overwintering– and those habitats’ interconnections shift? Golden wrote: “Due to climate change and human development in the Arctic, this species faces increased disruption to their life cycle, which might in turn impact survival and persistence.”

Developments like increasing instance of drought, altered precipitation rates, or the influx of sediment and nutrients that comes with a thermokarst-driven landslide are potential challenges. Habitat changes can have strong repercussions because of the Arctic graylings’ reliance on multiple habitats with strong interlinkages. They require “The ability to get from one location to the other at specific times during the year,” Golden said. “The only way they can do that is through water courses and only at certain periods of time. So if the river happens to go dry during a critical movement period, they will be unable to reach essential habitat.” Droughts can disrupt fish highways. Lowered water levels can enforce a harsher deadline when waterways begin the process of freezing solid from the top down.

For an Arctic grayling trapped somewhere in the Kuparuk river when winter’s hold firms, death looms as a likely fate. But Golden’s work suggests a different possibility: there may exist alternate overwintering habitats that offer fish a bit more of a fighting chance.

Aufeis and river springs

I’ve rarely heard mention of aufeis. It’s familiar to snowmobile enthusiasts, for whom aufeis can pose a dangerous challenge. PolarTREC (Teachers and Researchers Exploring and Collaborating) Biology and Environmental Science teacher Melissa Barker joined Golden for a day in the field near Toolik Research Station. She noted that “In German Aufeis means, ‘ice on top’, which aptly describes the layered ice formation. An aufeis forms when warmer spring water flows up from the ground and freezes in layers.” Remember that rivers freeze from the top down. The ‘ice on top’ or ‘overflow ice’ results when water in the diminished channel meets an obstruction and can no longer flow forward. Instead, the water forces its way up. It spreads, widening the icy area, and freezes in the frigid Alaskan winter air.

Golden said “The water holds enough thermal energy, just a degree above freezing, it doesn’t have to be much,” and “Where we find this characteristic aufeis we often find springs.” Sometimes the liquid water from the spring is totally covered over by ice. Other times the spring is warm and prolific enough to enforce open water in which case Golden said it’s “Truly like an oasis in the desert,” attracting all sorts of wildlife. Those springs can provide “The only flowing water sources during the winter for miles around.”

Havens of liquid water created by spring-fed water could provide alternate overwintering sites. “Perhaps some grayling would survive in these pockets of unfrozen water,” Golden asserted, “…Pockets of liquid water that might sustain fish over winter when all else is frozen.”

Pinpointing fish

Passive Integrative Responder (PIT) tag
Passive Integrative Responder tag that will be injected into a fish / Image Melissa Barker (PolarTREC 2012), Courtesy of ARCUS

It is important to gather hard data about where Arctic grayling move and when. Golden collaborated with Dr. Linda Deegan, senior scientist at the Marine Biological Laboratory, to inject PIT tags into grayling. A PIT tag is a Passive Integrative Responder tag, a coated wire tag (much like the type you can have implanted in a pet dog). Barker described “This process of inserting a PIT tag takes about three minutes and does not hurt the fish.” Once in place, the PIT tag can be detected by means of an external antenna. “They have 10 PIT antennas throughout the Kuparuk River. When a fish swims past the antenna, the PIT tag transmits a unique signal that is recorded,” Barker said. “This way they can get a sense of fish movement throughout the stream over the course of the year.”

Part of Golden’s work entails maintaining the equipment which detects the movement of PIT-tagged grayling. An antenna is connected to a tuner box – the antenna has to be tuned carefully to the correct frequency (something like an old car radio) to detect the PIT tags. Antenna wire arranged in a loop formation detects PIT tags as fish swim by (the wire is anchored to the stream bed by hammered-in rebar). A reader box collects and stores data until a scientist can retrieve it. Solar panels are used to charge marine batteries, which provide power to the rest of the equipment. And a bear fence surrounds the array to deter Alaska’s legendarily curious bears.

These stations sit next to streams or rivers, painstakingly set in place to detect passing Arctic grayling. In her work Golden also utilized a portable snowmobile-pulled system to find fish during the winter, a clever tactic. “We put a remote antenna array on the back of a sled and, instead of having an antenna in the river, actually dragged the antenna over the river. We were looking for fish under the ice.”

mobile antenna seeks fish
The mobile antenna dragged over river ice on a sled by snowmobile, and dragged by hand while snowshoeing / Image Heidi Golden

Golden and Cameron MacKenzie, research assistant, Ecosystems Centre, Marine Biological Laboratory, Woods Hole, looked at satellite imagery and thermal imagery to map out potential areas along the river near aufeis where fish might overwinter. Then they dragged their remote antenna array along those locations. The method worked; they found fish. Golden said in one fieldwork entry: “We actually found 3 tags under the ice. And each of these tags were associated with these seeps that we had pinpointed from the thermal imagery. So that was a huge Eureka.” The PIT tag locations matched up with places where heat signatures indicated there was liquid water under the ice.

Arctic water sampling spring
Heidi Golden collecting data (water conductivity, temperature, pH, water samples for for microchemistry analysis) from the lower Oksrukuyik aufeis spring / Image Heidi Golden

Yet the results weren’t entirely clear. Golden said “We did find the one area where there was open water and fish. We found numerous areas where there was aufeis and we found some areas where there was aufeis, open water and no fish. So fascinating!” Understanding the trends would require further investigation. When fish are present, Golden intends to find out “Whether they’re there by chance or by design.”


Any pool where a fish overwintered would require enough oxygen to keep the fish healthy. Where Golden and MacKenzie found fish at the Kuparuk Upper Spring pool, Golden recorded “The water was only knee deep; it really does not take a lot of water to hold fish.” Still, such a shallow depth was surprising. “We were suspecting that they need to get to these deep pools or a deep lake, and we know if the lake is not above 4 meters deep that it likely cannot sustain fish over winter,” because of insufficient oxygen. The shallow depth of water Golden and MacKenzie encountered suggests there is a flow of water, likely from the spring, supplying oxygen.

Arctic grayling spring water snow
“Although the KUS pool is often barely recognizable as a spring, fish were milling about in the shallow water, moving back and forth from under cover of the ice to fully visible in the open water. Soon the anchor ice confining the main-stem of the Kuparuk will give way with warming temperatures and melt water pressure. At this time, the KUS pool will rejoin the main river and despite it’s importance to overwintering fish, this portion of the stream will look inconsequential.” / Image Heidi Golden

The spring doesn’t necessarily keep the fish safe from hungry foxes or hawks, but it does provide an oasis of sorts that might help more members of the species persist in a variable climate. “If there are a lot of these locations,” Golden noted, ”Then that would suggest that grayling actually survive in a lot of locations. Perhaps that could be a safety net in climate change where they can’t get to their overwintering site.”

Then again, Golden witnessed dead grayling under the ice at the springs. Maybe they became lunch for a predator or, she said, “It is possible that they just ran out of resources and just didn’t survive.”

Perhaps at times when Golden’s portable antenna array picked up on PIT tag signals, the PIT tag indicated not that an adult Arctic grayling was present but that the spot had been used as a spawning location. Golden outlined “It could be that there is actually a fish under the ice,” but “There is a tag loss rate.” Golden: “We tag the fish in the abdomen, and if it is a female it’s possible that the female could then spawn that tag out. But the exciting thing about that is if it is a spawned-out tag then it could indicate that those locations are actual spawning sites.”

Aside from providing a dubious oasis for adult Arctic grayling fish, these alternate overwintering habitats may play host to tiny semi-transparent ‘young of the year’ (YOY), grayling recently spawned. Golden speculates that at these small springs YOY may “Survive their first winter. Which I think is a critical stage for survivorship of a population.”

“Because rivers freeze solid in winter, locations or larval overwintering habitat might be of particular importance,” Golden explained. “We might be able to locate critical spawning areas and discover where larval fish spend their first year of life. I think those habitats are critical for sustaining a population of graying on the North Slope.”

Green Cabin Lake Alaska
Approaching Green Cabin Lake, the headwaters of the Kuparuk River, by helicopter / Image Melissa Barker (PolarTREC 2012), Courtesy of ARCUS

In the field

“The aquatic landscape is changing. How will this landscape-level change affect the fish populations living within this aquatic network?” Golden’s work is designed to investigate that question. And the work continues. She’s not only tracking Arctic grayling with PIT tags. She’s also taking fin clip tissue samples to analyze genetics, chemically analyzing water samples from different locations and comparing them to the chemical composition of fish ear bones called otoliths, studying recently spawned ‘young of the year’ grayling, delineating and mapping Arctic grayling movement patterns and genetic populations.

It’s in-depth work that ranges over many kilometers; Golden and associates travel via foot, snowshoe, snowmobile, truck and even helicopter. On clear days the Brooks Mountains are beautiful in the background. I absolutely love getting to see Golden’s field work documented in her online journal. It’s such a treat to see science in action!

Also learn more about the aufeis and alternate overwintering habitat in this FrontierScientists video: Grayling Under The Ice.

Golden’s Arctic grayling research is funded through the National Science Foundation, the Arctic Long Term Ecological Research Network, the U.S. Fish and Wildlife Service, the U.S. Environmental Protection Agency (EPA-STAR Fellowship), and the University of Connecticut. Logistic and technical support provided by the Marine Biological Laboratory, Woods Hole Oceanographic Institute, the University of Alaska Fairbanks, and Toolik Field Station.

Laura Nielsen

Frontier Scientists: presenting scientific discovery in the Arctic and beyond

Grayling project

  • Interview with Heidi Golden, Ph.D. candidate at the University of Connecticut, July 2014
  • ‘Arctic Research and Exploration’ Heidi Golden, Archives from 2013 field work
  • ”Will Climate Change Influence the Metapopulation Dynamics of the Arctic Grayling?’ EPA Grant Number: FP917459, Investigator: Golden, Heidi E, Project Period: August 1, 2012 through July 31, 2015
  • ‘Day Off’ Melissa Barker, Nutrient Transport in Arctic Watersheds Journals, 21 May 2012, PolarTREC: Teachers and Researchers Exploring and Collaborating
  • ‘Helo to Work’ Melissa Barker, Nutrient Transport in Arctic Watersheds Journals, 6 June 2012, PolarTREC: Teachers and Researchers Exploring and Collaborating
  • ‘Will Climate Change Influence the Metapopulation Dynamics of the Arctic Grayling?’ EPA Grant Number: FP917459, Investigator Heidi E Golden, Project Period August 1, 2012 through July 31, 2015