Eulachon use habitats in both rivers and the ocean. Eulachon appear to be susceptible to poor water quality because they easily incorporate toxic substances such as heavy metals (reviewed in Willson et al. 2006).
Most spawning occurs within tidal influence though some spawning areas are located much further upstream of the river mouth. Spawning migration is initiated when temperatures are above 4°C, but slows or stops outside the range of 4-8°C (Morrow 1980, Emmett et al. 1991). Spawning is also initiated by spring high tides or flows (reviewed in Willson et al. 2006). During the spawning migration, the adults travel along the bottom of estuarine and river channels (Emmett et al. 1991) and shallows at the water’s edge (T. Kisanuki, pers. comm.). Spawning occurs in habitats with moderate water velocities, 4-10°C water temperatures, and small substrate (pea-sized gravel or semi-sandy areas) near woody and other debris (Emmett et al. 1991). Salinity greater than 16 ppt and temperature changes of more than 6°C over a few days are lethal to eggs (reviewed in Willson et al. 2006). Eggs hatch in 19 days at 8.5-11.5°C, and in 30-40 days at 4.4-7.2°C (Emmett et al. 1991).
In the Ocean
In the ocean, Eulachon appear to live near the bottom of the continental shelf, usually at depths of 20-200 m, although they have been found at depths up to 625 m (reviewed in Willson et al. 2006).
Size and Weight Range
Size and Weight Range Spawning adult size range: most adults reach 20 cm total length (TL) and a few reach 30 cm TL (Moyle 2002). Females are usually significantly smaller than males by 4-8 mm (Moffitt et al. 2002). Spawning adult weight range: 40 to 60 grams with a maximum weight of 75 grams.
Dorsal fin: 10 to 13 rays
Anal fin: 18 to 23 rays
Pectoral fin: 10 to 12 rays
Pelvic fin: 8 rays
There are 70 to 78 scales along the lateral line.
The lateral line has 70 to 78 scales.
Number from 8 to 12.
7 to 8 rays.
17 to 23 thin gill rakers on the first arch.
Larvae washing out of streams transform into free-swimming juveniles at about 50 to 80 mm total length (TL). They grow 40 to 50 mm per year for the next 3 years and mature to adults when they reach a length in the range of 14 to 20 cm TL.
Eulachon have long compressed bodies that are brown to dark blue on the back and head with a silvery white belly and unmarked fins. Their flesh is very oily. They are the largest smelt on the Pacific coast of North America. They have large oblique mouths; the maxilla reaches past the middle of the eye and can extend beyond the posterior margin of the eye in adults. Their jaws have small pointed teeth, which may be missing from spawning fish, especially males. Small teeth are also present on the tonque and palatines. They can be distinguished by large canine teeth on the bone in the roof of the mouth called the vomer. They can also be identified by noticeable concentric striations on the gill covers, and pectoral fins that reach about two-thirds of the way to the base of the pelvic fins when flat against the body. Spawning males develop a distinct midlateral ridge and numerous distinct tubercles (raised tissue bumps) on the head, body, and fins. Tubercles are poorly developed or absent in females. 17 to 23 thin gill rakers on the first arch.
Eulachon are anadromous but spend most of their life in the ocean. They spend only a few weeks in fresh water at the beginning and end of their lives. Spawning migrations are likely initiated by changes in water temperature, spring freshets and the occurrence of high tides (reviewed in Willson et al. 2006). In California, spawning migrations usually occur between December and May in association with high spring tides (Cannata 2009). In the Klamath River, most eulachon spawn in March and April within 10 to 12 km of the river mouth. Spawning migration commences when river temperatures are above 4°C but slows or stops if the temperature drops below 4°C or exceeds 8°C.
Spawning and Egg Development
Males arrive at spawning grounds earlier than females. Eulachon spawn en mass at night (Hay and McCarter 2000, Moyle 2002) at depths ranging from 0.3 to about 8 m, depending on location (reviewed in Willson et al. 2006). Eggs are fertilized externally by sperm that is likely viable only for a few minutes (Hay and McCarter 2000). Consequently, males and females have to be in close proximity for fertilization to succeed. Fecundity depends on female size and varies from 7,000 to 60,000 eggs (Wydoski and Whitney 1979, Emmett et al. 1991), with most females producing an average of 25,000 eggs (Moyle 2002). After spawning, most die although a few may live to spawn again in a consecutive year (Barraclough 1964, Hay and Carter 2000). Upon fertilization, the outer of the two egg membranes ruptures when the egg hits the bottom, allowing its adhesive edges to stick to the substrate.
Larvae and Juveniles
The outer and inner membranes of the egg are attached by a short stalk to the substrate so that the egg is anchored to the bottom until it hatches in two to three weeks (Carl and Clemens 1953, Hay and McCarter 2000). The transparent larvae are 4 to 7 mm TL. Larvae stay mid-water or near the bottom and are quickly washed out to sea. Larvae may also rear in estuaries before emigrating to the ocean. At temperatures of 53°C yolk sacs are absorbed within 21 days.
Larval Emigration and Eulachon in the Ocean
Ocean currents widely distribute larvae once they reach the ocean. Larvae transform into juveniles in their second year. Immature fish stay in coastal waters where they feed on euphausiid and other copepods, as well as other crustaceans for the next two to three years (Barraclough 1964, Emmett et al. 1991).