Eulachon, the Candlefish: A First Look at Alaska's Taiya River Run

Each spring in Southeast Alaska people and wildlife wait for the same event: silvery schools of a small, nutrient-rich fish. Alaskans call it hooligan or candlefish, and biologists call it eulachon (Thaleichthys pacificus), an anadromous smelt that feeds and grows in the cold North Pacific and runs up rivers in spring to reproduce. One of those rivers is the Taiya, which flows from the Coast Mountains through Klondike Gold Rush National Historical Park to an estuary near Dyea, a former gold rush town. Sarah Apsens (Alaska Department of Environmental Conservation), Andrew Waldo (Alaska Department of Fish & Game) and Jami Belt (National Park Service) report the first survey of the Taiya's eulachon, which found low abundance in both years.

Eulachon migrating upriver to spawn (NOAA Fisheries).

A fish that fed people and wildlife

Oil, medicine, food and trade goods from this small fish shaped generations of Indigenous peoples, and anthropologists consider eulachon a keystone species of West Coast Native culture. Runs come when food supplies historically ran low, so some tribes called them salvation fish. The buttery oil is made by fermenting large quantities of whole fish and extracting the oil, which is added to other foods or taken alone as medicine. Up to 20% of the fish is fat, and when dried it can be lit as a light, hence candlefish. Before the gold rush, Alaska Natives used the Chilkoot Trail and similar trails to trade eulachon oil with interior neighbors, and the trails were nicknamed grease trails. About 30,000 people crossed the Chilkoot during the 1890s gold rush. Subsistence fishers harvest eulachon throughout Southeast Alaska; in Haines and Klukwan 95% of households reported using them, with a reported harvest of 162,060 pounds in 2012. Little is known about subsistence use on the Taiya or in Skagway.

Wildlife depends on the fish too. Spring runs arrive when sea lions, river otters, harbor seals and migrating shorebirds have high energy needs, and all of them feast on eulachon; whales, dolphins, sharks, bears, wolves, ravens, eagles, seabirds and salmon also take them. A 2002 study found that predator numbers rose rapidly at the start of the runs and tracked an index of eulachon abundance within years. Because eulachon return when other prey is scarce, they are considered an ecological cornerstone of coastal systems.

Life cycle in brief

Most eulachon, like salmon, die soon after spawning once. They spawn in spring in the lower reaches of rivers at age 2 to 5, when they are about as long as a pencil (6.3-9.8 inches or 160-250 mm). A female broadcasts 7,000 to 60,000 eggs over gravel or sand, and the sticky eggs hatch in 3 to 8 weeks, faster in warmer water. Eulachon spawn in river temperatures from 32 to 50 degrees Fahrenheit (0 to 10 degrees Celsius), including under ice.

Why the Taiya matters

Eulachon once ranged from northern California to the Alaska Peninsula and southeast Bering Sea, but southern runs are severely depleted or extinct. In 2010 the population spawning in California, Oregon and Washington was listed as threatened under the Endangered Species Act, and populations south of the Nass River in British Columbia are of special concern. Changes in ocean conditions, loss of spawning habitat in quantity and quality, and overfishing are all linked to the declines. Because the fish is not commercially harvested, basic data are missing for most populations. The Taiya also has hydroelectric potential, which could affect the species. Fewer than 60 Alaskan rivers are thought to host anadromous runs, and studies exist for some Southeast Alaska rivers but not for the Taiya. After the Chilkoot Indian Association and the Takshanuk Watershed Council studied the nearby Chilkoot River from 2010 to 2016, park biologists, the Skagway Traditional Council and the Taiya Inlet Watershed Council started the Taiya study.

The 2017 and 2018 survey

Biologists set a fyke net in mid-April and fished it in daylight five days a week, for one hour at each incoming, outgoing and slack tide. They counted, sexed, weighed and measured the fish and returned them to the river, except for a subset of females sacrificed to measure fecundity. They noted sea lions each day before sampling, since sea lions indicate run strength, and sampled larvae and eggs weekly at 10 sites beginning three weeks after the first adults were caught.

Sea lions were far fewer than in 2016, when 75 were seen at the site, which indicates a larger run that year. The authors stress that two years cannot show a trend, and that some eulachon runs are reliable from year to year and others sporadic. In the Chilkoot River, total abundance swung widely between 2010 and 2016, from 319,586 to 12.6 million fish. A full census takes more people and money than Klondike Gold Rush park has, so the authors suggest weighing the cost and usefulness of genetic tools such as eDNA if abundance is estimated again; a 2020 test using eDNA samples from the 2017 Taiya run gave promising results.

Size, sex ratio and fecundity differed between the years, and such traits can hint at population health: heat or a lower food supply can raise mortality and favor a younger, smaller, less fecund spawning population. Fecundity was comparable to that of other Southeast Alaska populations, giving the first life-history baseline for the Taiya. No larvae or eggs turned up in or above West Creek, which suggests no spawning there. The farthest upriver eulachon were found at the bridge south of the Beaver ponds, about five river miles from the estuary and well above tidal influence, contrary to numerous studies saying eulachon spawn only in tidal reaches. That information could help protect essential habitat if hydroelectric or other development comes.

An uncertain future

The Gulf of Alaska is predicted to become more acidic and warmer. Acidification may affect the fish's prey, and warming water can speed metabolism and change growth and maturation, run timing, egg incubation and mortality. The authors say the survey gives only a first glimpse of the Taiya's eulachon, and that their persistence will likely depend on adapting to change and on conserving their essential habitat.

Sources

• Sarah Apsens (Alaska Department of Environmental Conservation), Andrew Waldo (Alaska Department of Fish & Game) and Jami Belt (National Park Service), Eulachon: A little fish with many names and a big ecological impact, Alaska Park Science 19(1), National Park Service, 2020; rewritten in hubnx's own words.