Eulachon
Thaleichthys pacificus
Profile / Morphology 2
Eulachon are anadromous, migrating from the ocean to spawn in fresh water. They usually spawn only once and then die (called semelparity) but some individuals can be iteroparous and return for at least one additional spawning season. Adult coloration is brown to blue on back and on the top of the head, with the sides lighter to silvery white, and the ventral surface (the underside) is white. The fish change to a gray-brown around spawning time. They have fine, sparse speckling that is restricted to the back. A fleshy adipose fin found between the dorsal fin and the tail (like salmon) is sickle-shaped. They are distinguished by large canine teeth on the vomer (in upper part of mouth) bone (although this is lost as the fish reaches spawning time) and 18 to 23 rays in the anal fin. The paired fins are longer in males than in females and all fins in ripe males have well developed breeding tubercles which are poorly developed or absent in females. During spawning, male fish have a distinctly raised ridge along the middle of the body and a rough texture, differentiating it from the female which is smaller, smoother and shinier.
Diet 3
Adult eulachon feed on plankton, mainly euphausid shrimps (krill), but only while in the ocean, not during freshwater spawning runs. Newly hatched young feed mainly on copepod larvae and other plankton during their downstream movement to the sea.
Average lifespan in the wild 3
5 years
Size / Weight 3
13 inches (33 cm) maximum / 5 lbs (2.3 kg) maximum
Habitat 3
Found near shore to 300 m depth and in coastal inlets and rivers during spawning season. There is evidence that the species is subdivided into multiple populations.
Range 3
Eulachon range from northern California to southwest Alaska and into the southeastern Bering Sea.
Reproductive / Lifespan 3
Smelt typically spend three to five years in saltwater before returning to freshwater to spawn in late winter through mid spring. The spawning run from the sea to freshwater streams begins when river temperature rises to about 4.5°C, but the fish stop running if temperature exceeds 8°C. Males predominate in the early part of the run, but their numbers are equaled by females later. Males are distinguishable from female at spawning time by the presence of tubercles on the head and on the scales along the lateral line, more muscle development along the lateral line, and longer pectoral and pelvic fins. Eggs are broadcast over sandy gravel bottoms where they attach to sand grains. Adults usually die after spawning but some move back to the sea and return to spawn a second time. Upon hatching (after a 20-40 day incubation period), larvae are found near the bottom and are soon carried downstream to salt water and eventually found in the scattering layer of coastal waters. Adults may return to their stream of origin to spawn and die or may return to streams near where they were born. Eulachon can live up to five years
Relatives 3
There are four other species of smelt in Alaska and four others in the Pacific Northwest that overlap with eulachon. The eulachon is distinguished from other Alaska smelts by having the front of the dorsal fin begin well behind where the pelvic fin is attached to the body (similar to jack silverside smelt in California and Oregon) and by having circular grooves on the gill covers.
Found in the following Esturine Reserves 3
Kachemak Bay (AK), Padilla Bay (WA), South Slough (OR), San Francisco (CA), Elkhorn Slough (CA)
Water Quality Factors Needed for Survival 3
•Water Temperature: 4 to 25°C
•Turbidity: low to moderate
•Water Flow: low to moderate
•Salinity: 0 to 35 ppt
•Dissolved Oxygen: moderate to high
Threats 3
There has been a long decline in population sizes for this species with the decline steepening in recent years. Population size typically changes considerably from year-to-year but there has been consistent declines in nearly all spawning runs from California to southeastern Alaska over the past 20 years.
Primary threats include:
•Excessive historic fishing
•Bycatch
•Habitat loss and degradation
•Dams and other impediments
•Water development projects
•Pollution
•Climate Change
Eulachon were fished both commercially and recreationally. Eulachon harvest has been curtailed significantly in response to population declines. However, existing regulatory mechanisms may be inadequate to recover eulachon stocks.
From 1938 to 1992 in the Columbia River (the largest spawning population), the median commercial catch of eulachon was approximately 1.9 million pounds (861,826 kg) but this declined to approximately 43,000 pounds (19,504 kg) on average for 1993 to 2006. This represents a 97.7 percent reduction in catch from the prior period. Similarly, the number of eulachon that returned to the Fraser River and other British Columbia rivers suffered severe declines in the mid–1990s and, despite increased return levels during 2001 to 2003, presently they remain at very low levels.
Habitat loss and degradation also threaten eulachon, particularly in the Columbia River basin. Hydroelectric dams block access to historical eulachon spawning grounds and affect the quality of spawning substrates through flow management, altered delivery of coarse sediments, and siltation. Siltation of spawning substrates in the Cowlitz River is a concern due to altered flow management and the accumulation of fine sediments from the Toutle River. Efforts to retain and stabilize fine sediments generated by the 1980 eruption of Mount St. Helens may be inadequate as the release of fine sediments from behind a U.S. Army Corps of Engineers sediment retention structure on the Toutle River has been negatively correlated with Cowlitz River eulachon returns three to four years later. Dredging activities in the Cowlitz and Columbia rivers during the eulachon spawning run may entrain and kill fish, or otherwise result in decreased spawning success.
Eulachon have also been shown to carry high levels of chemical pollutants, and although it has not been demonstrated that high contaminant loads in eulachon result in increased mortality or reduced reproductive success, such effects have been shown in other fish species.
Conservation notes 3
Importance to Humans and Estuaries
Eulachon were fished both commercially and recreationally. These fish are also called “candlefish” because traditionally the whole fish was dried and fitted with a wick and used as a candle. This worked because of the fish’s high oil content during spawning where up to 15% of its total body weight is fat!
Until the early 1900s, large numbers of natives gathered on rivers with major migrations of eulachon to dry them and extract the oil from their flesh with simple presses. They were important as a food staple and as barter with inland tribes, leading to the famous "kleena" or grease trails of Southeast Alaska and British Columbia.
Additionally, native Indian tribes along the coast use them for food and other uses and they play a significant role in cultural practices in many tribes in the region. In many areas they occurred in high numbers, and because of their migratory lifestyle, they were a significant source of nutrients being brought into and out of estuaries where they served as prey for many larger animals including salmon, sturgeon, marine mammals, and a variety of birds.
How to Help Protect This Species
Because this species uses estuaries and freshwater areas it is susceptible to water pollution and damage to and alteration of stream channels and riparian zones. Therefore, efforts to protect the species include:
•Minimize runoff of neighborhood pollutants, fertilizer, and sediment into local streams are helpful to this species, and other estuary dwelling species.
•Join a stream or watershed advocacy group in your area to protect your local estuary ecosystems.
•Advocate the implementation of effective fish passage solutions so fish can bypass dams and artificial barriers.
•Support restoration of more natural water flow regimes.
•Support research into the ecology and conservation of the species.
Sources and Credits
- (c) BIO Photography Group, Biodiversity Institute of Ontario, some rights reserved (CC BY-NC-SA), http://www.boldsystems.org/archive/image.php?id=bold.org/37874
- Adapted by GTMResearchReserve from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Thaleichthys_pacificus
- (c) GTMResearchReserve, some rights reserved (CC BY-SA)
