Linda Deegan was looking for something different, a unique experience to fill the space between completion of her dissertation and the start of her new faculty position at the University of Massachusetts. A friend suggested flying to Alaska and helping him study the ecosystems in streams of the tundra near Toolik Lake. She would be in a picturesque and unique environment studying Arctic grayling: a fish that she now describes as “captivatingly beautiful.” Twenty years later, as part of the Arctic Long Term Ecological Research (ARC LTER) project, she’s still studying grayling, pondering the impacts of climate change on this species and its habitat.
Researcher: Linda Deegan
University/Organization: The Ecosystems Center at the Marine Biological Laboratory, Woods Hole, Massachusetts
Research Location: Kuparuk River in Alaska
MEET THE ARCTIC GRAYLING
The Arctic grayling (Thymallus arcticus) is a medium-sized fish, in the same family as salmon and trout, but with enough unique characteristics to be placed in a subfamily of its own – Thymallinae. Grayling live in cold-water streams and lakes and are easily recognizable by their long dorsal fin and iridescent blue-purple color. In males, the dorsal fin becomes even more colorful during the spawning season.
An exceptional grayling can weigh up to 1.3 kg (approximately 3 pounds) and grow to 50 cm (20 inches) long, but the fish Linda Deegan studies in Alaska more typically average 400 grams (14 ounces) and 30-40 cm (12-15.7 inches).
Arctic grayling are native to river systems that drain into the Hudson Bay and the North Pacific and Arctic Oceans from both North America and Asia. Two native populations exist in Asia, one in the area of Lake Baikal, in southern Siberia, and the other in the Amur Basin in eastern Asia.
Although grayling are now synonymous with the wilds of Alaska, they were described by Lewis and Clark in 1805 in the upper reaches of the Missouri River, in what is now Montana. Grayling were also plentiful in streams and lakes in Michigan in the late 1800s, but they were already in decline by 1900 and became extinct there by 1930. A historical marker near Grayling, Michigan, says the fish drew sportsmen from “the country over.” Attempts to reintroduce grayling to streams in Michigan between 1987 and 1991 were unsuccessful.
Two subspecies of grayling are still found in Montana, but they rarely have life spans of more than five years. In the Brooks Range region of northern Alaska, Arctic grayling can live to be 18-20 years old! The oldest fish that Linda’s group has captured was 22 years old. This is all the more remarkable given that the fish can only live in the streams when temperatures are warm enough to allow water to flow. During the three short months of summer, they feed on the insects drifting on the surface of the streams. During the rest of the year, they live on the fat that they accumulated during the summer season.
As the sun and the temperatures drop in the early fall, the streams across the region freeze solid. Before that happens, grayling must migrate to a lake where they can spend the winter months in the water below the ice.
As the temperatures warm and the ice and snow melt in the spring, the grayling return to the streams to feed and to spawn. Because the short Arctic summer season (two summer months) limits their ability to grow, Alaska grayling are also elderly spawners – it takes five – eight years before they are large enough to spawn.
STREAMS IN THE TUNDRA
Linda conducts her research in the Kuparuk River, located in the foothills north of the Brooks Range.
The river is about 150 km (93 miles) long, but access is quite limited. The only road in the area intersects the river at only two locations, near the headwaters and near the coast. Linda and her research assistant must travel by helicopter to study any area between these two points.
The tundra is a very interesting environment. Permafrost (ground that remains at or below freezing for at least two years) creates a continuous layer in the soil under much of the Arctic region (see map at http://nsidc.org/fgdc/maps/ipa_browse.html). Water that permeates the soil or peat can only soak downward until it reaches the permafrost layer, and then it travels along the permafrost. The runoff water eventually forms streams and collects in low areas as ponds and lakes.
HOW DO ARCTIC GRAYLING SURVIVE?
In May, the adult grayling migrate from lakes back into streams to spawn. The young grayling hatch around the first of July, and grow quickly throughout July and August. Linda has observed some small fish (2 inches in length) hiding behind rocks, and thereby reducing the amount of energy needed to maintain a position in the water and feeding in the “slipstream” as insects fly along the water surface above. This is an excellent survival strategy, one that has obviously worked well for the grayling.
The fall migration to the lakes occurs from late August through September. There the grayling must share the lakes with other fish, including the predatory lake trout.
LAKE TROUT VERSUS ARCTIC GRAYLING
Lake trout, sometimes referred to as “lake char,” are the top predators in the tundra lake ecosystem. Lake trout can weigh as much as 66 pounds. They are visual predators; they need to see the smaller fish on which they feed. The arrival of the migrating grayling in the fall provides a rich source of proteins and lipids (fats and oils) that both nourish the trout and enrich the nutrients in the yolk sacs of their eggs.
About a month after the first of the grayling arrive, the trout lay their eggs in the bottom of the lake. By the time the younger and smaller grayling arrive, the trout have already gorged themselves on the larger and older graylings, so they’re not as hungry. Furthermore, the light becomes dimmer and dimmer as the sun sets in the fall, reducing the ability of the trout to find their prey. This combination of factors gives the younger grayling a better chance at survival by arriving at the lake after the larger grayling.
Both Arctic grayling and lake trout are edible fish. Lake trout are large and tasty; the grayling are not as large or as tasty. As a result, grayling are often released by sport fishers in Alaska. However, native people typically harvest the grayling in the spring as an attractive, easily caught food source at a time when other wild food is less available.
LEARNING MORE ABOUT THE ARCTIC GRAYLING
Linda and her assistants tag adult graylings each year as they migrate into the lake and count the just-hatched young fish. They also recapture tagged adult fish and weigh them year after year to learn how fast they grow during cold years, warm years, wet years, and dry years. The fish are captured with a fly rod and with net barriers across the stream.
The researchers also capture some of the lake trout from two lakes in the region. One of the lakes, Green Cabin Lake, has a grayling migration and the other, Toolik Lake, does not. Measurements of length and weight are used to compare the “condition factor” of the two trout populations, ultimately providing an indicator of how robust the Green Cabin Lake fish are as a result of greater food availability from the grayling.
Linda and other researchers have found that the juvenile grayling (4 to 8 inches, 2 to 4 years old) go to smaller streams in between their “young-of-the-year” stage (first season of life) and the stage when they are old enough to spawn (at around 20 cm or 8 inches). The larger adultfish arrive at the lakes first, followed by smaller juvenile fish. Recently, she also observed that the smaller fish arrived in a pulse (about 2,000 fish in one day) and then just a few were seen over the next two to three days.
One mystery that has baffled Linda for 20 years is where the young-of-the-year spend the winter. A small fish moving into a lake filled with predators doesn’t seem like a good choice – and Linda has never seen it happen – but what other options do the young fish have? She acknowledges that she has not been present when the migration completely shuts down in the fall. As a result, she has not seen the very last of the fish arrive at the lakes. Is it possible that the smallest fish (the young-of-the-year) come into the lake during the last few hours before the stream freezes solid and winter darkness limits the ability of lake trout to eat them? If not, how and where do they survive the harsh winters?
Another puzzle lies in the fact that some Arctic grayling must migrate upstream to reach a lake, while others in another part of the stream must migrate downstream. Linda and other scientists wonder: How do they know which way to go? Can they change if the environment changes or are they genetically programmed?
Ecology is the study of interactions among and between the biological and physical factors in the environment. In addition to the seasonal variations in temperature and available light, scientists gather data about the populations living there to study their reproductive and overwintering successes, the transfer of nutrients, and the influences of human interactions.
Having a record of conditions over a period of time allows scientists to consider the importance of specific environmental factors. For example, during a dry year, as the water level drops, a stream can be broken into a series of disconnected pools. A number of grayling can become stranded in the pools. As the water level continues to drop, the fish congregate in a smaller volume of water. Furthermore, as the temperature of the water increases, the dissolved oxygen in the water decreases. This means that the fish in a small pool can use up the available oxygen quickly. During prolonged periods of drought, adult grayling stranded in isolated pools in a stream may die.
The adults are well adapted to cold water but warmer temperatures cause “thermal stress.” They stay closer to the bottom of the stream, become inactive, and stop feeding at a time when their metabolism is increased by the warmer temperatures. The average summer temperature of the Kuparuk River is between 8-10 degrees Celsius, but when the water approaches 15 degrees Celsius, the adult grayling become lethargic.
In contrast, the young-of-the-year survive better in warmer, drier years. The temperature of the water is higher, but there’s less flow. As a result, the fish don’t have to swim as hard to stay in position. As long as insects are available, the young thrive and grow well, even as the temperatures approach 20 degrees Celsius.
In the long run, it is important for this species to have a few good cool years for the adults and a few warmer years, which seem to be an advantage to the youngest fish. Hypothetically, an ideal situation would be alternating periods of warm and cool summers. There have been periods when seasonal cycles allowed a fairly high population of grayling to develop. The current numbers of grayling are relatively low in the Kuparuk River region. Conditions haven’t been ideal in the last few years due to the changing climate.
In 2007, the largest fire ever recorded north of the Brooks Range burned 256,000 acres and continued until the end of September when nearby lakes had already frozen over. The fire, at least partially the result of a severe drought, was an example of an extreme event. Linda and other scientists found that the insect food for grayling was less abundant in the burned streams in the first year after the fire. It is too early to tell if the fire has had long-lasting effects on the river system and on the grayling population, but the fire presents an opportunity to test ideas about the resiliency of the stream and lake system to extreme events.
Linda and her colleagues wonder what is in store for the Arctic grayling of the Kuparuk River region as the climate continues to change. More questions always arise as scientists gain new understanding. Linda has used instruments to measure flow and water levels in the streams, but instruments can’t help with the measurement of water quality, which may influence the survival of the grayling. She would also like to put cameras in the water where the streams enter the lakes to monitor the last of the in-migration.
Improved imagery from satellites has led Linda to wonder if small areas of open water, such as those near springs in the streambed, might be sufficient for the young-of-the-year to survive without actually traveling to a lake. Grayling do not have the anti-freeze proteins that would allow them to survive freezing temperatures, but maybe small fish can survive in small amounts of liquid water.
Perhaps the Arctic grayling of Alaska will begin to have separate populations of lake-dwelling and river- or stream-dwelling fish. Perhaps the winters won’t be as harsh and the fish will survive in the deepest parts of the streams. Maybe drought and other extremes will become more common, bringing about other changes in the survival rates of the lake trout and the Arctic grayling.
Linda’s work with the Arctic grayling is an excellent example of the value of conducting long-term ecological research. Occasional monitoring of a region doesn’t help to explain changes that occur over a period of years. Annual studies of an area over decades allow scientists to record conditions, enabling them to detect trends in the data, determine what levels of change are significant, and link changes to other ecological factors.
Copyright April 2009 – The Ohio State University. This material is based upon work supported by the National Science Foundation under Grant No. 0733024. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.This work is licensed under an Attribution-ShareAlike 3.0 Unported Creative Commons license.