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Eulachon

Secure  (NatureServe)[2]
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Osmeriformes
Family: Osmeridae
Genus: Thaleichthys
Girard, 1858
Species:
T. pacificus
Binomial name
Thaleichthys pacificus
Synonyms[3]
  • Lestidium parri Chapman, 1939
  • Osmerus albatrossis Jordan & Gilbert, 1898
  • Osmerus pacificus (Richardson, 1836)
  • Salmo pacificus Richardson, 1836
  • Thaleichthys stevensi Girard, 1858

The eulachon (/ˈjuːləkɒn, -lɪkən/;[4] Thaleichthys pacificus), or the candlefish, is a small anadromous species of smelt that spawns in some of the major river systems along the Pacific coast of North America from northern California to Alaska.

Etymology

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First ever documentation of this species recorded in the journal of the Lewis and Clark Expedition on February 25, 1806 at Fort Clatsop[5][6]

The name "candlefish" derives from it being so fatty during spawning, with up to 15% of the total body weight in fat, that if caught, dried, and strung on a wick, it can be burned as a candle.[7][8][better source needed] This is the name most often used by early explorers. The name eulachon (occasionally seen as oolichan /ˈuːlɪkɑːn/, ooligan /ˈuːlɪɡən/, hooligan /ˈhuːlɪɡən/, oulachon, and uthlecan) is from the Chinookan language and the Chinook Jargon based on that language.[citation needed] One of several theories for the origin of the name of the state of Oregon is that it was a corruption from the term "Oolichan Trail", the native trade route for oolichan oil. In some parts it is also known as "halimotkw", which can be translated as "savior fish" or "salvation fish", due to its availability for fishing often coming at the end of winter, when food supplies typically run low.[9]

The unrelated sablefish Anoplopoma fimbria is also called "candlefish" in the United Kingdom.

Species description

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Eulachon are distinguished by the large canine-like teeth on the vomer bone and 19 to 31 rays in the anal fin. Like salmon and trout they have an adipose fin (aft of the dorsal); it is sickle-shaped. The paired fins are longer in male fish than in females. All fins have well-developed breeding tubercles (raised tissue "bumps") in ripe males, but these are poorly developed or absent in females. Adult coloration is brown or blue on the back extending to the top of the head, lighter to silvery white or light blue on the sides, and white on the ventral surface; speckling is extra fine, sparse, and restricted to the back.[10] Adults can reach maximum lengths of 30 cm (12 in) but most adults are between 15 and 20 cm (6 and 8 in).[11] Adults have striae on their operculum that aid in distinguishing Thaleichthys pacificus from other smelt.[12] They feed on plankton but only while at sea.[10]

Ecology

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Eulachon feed primarily on plankton as well as fish eggs, insect larvae, ocean debris and small crustaceans. It forms an important part of the diet of many ocean and shore predators, and serves as a prominent food source for people living near its spawning streams.

Eulachon, as anadromous fish, spend most of their adult lives in the ocean but return to their natal freshwater streams and rivers to spawn and die.[13] As such, one stream may see regular large runs of eulachon while a neighboring stream sees few or none at all. Regular annual runs are common but not entirely predictable, and occasionally a river which has large runs sees a year with no returns; the reasons for such variability are not known. The eulachon run is characteristic for the early portion being almost entirely male, with females following about midway through the run to its conclusion.[citation needed] Males are easily distinguished from females during spawning by fleshy ridges which form along the length of their bodies.[clarification needed]

Economics and trade

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Eulachon rendering camp at the mouth of the Nass River, 1884.

Indigenous communities of the Pacific Coast from California to Alaska made eulachon an important part of their diet, as well as a valuable trade item with peoples whose territories did not include spawning rivers. The species was caught using traps, rakes, and nets. The harvest continues today, with other residents taking part in the exploitation of the large runs. Today harvested eulachon are typically stored frozen and thawed as needed. They may also be fried, dried, smoked, or canned. Eulachon were also processed for their rich oil. The usual process was to allow the fish to decompose (rot) for a week or more in a hole in the ground, then add boiling hot water and skim off the oil, which would rise to the surface, being less dense than water. Eulachon oil (also known as "Eulachon grease") was traded with inland communities; as a result, the trails over which the trade was conducted came to be known as grease trails. Other uses of eulachon by non-Natives include bait for sportfishing and food for cats and dogs.

Conservation status

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In November 2008, the National Marine Fisheries Service (NMFS) received a petition from the Cowlitz Tribe to list a distinct population segment (DPS) of eulachon from Washington, Oregon, and California, (the so-called Southern DPS) as an endangered or threatened species under the Endangered Species Act.[14] (ESA). NMFS found that this petition presented enough information to warrant conducting a status review of the species. Based on the status review NMFS proposed listing this species as threatened on March 13, 2009.[15] On March 16, 2010, NOAA announced that the Southern DPS of eulachon will be listed as threatened under the ESA, effective on May 17, 2010 (See: the Federal Register notice published on May 18, 2010, at 74 FR 3178).[16] On September 6, 2017, the NMFS approved a recovery plan intended to serve as a blueprint for the protection and recovery of the southern Distinct Population Segment (DPS) of eulachon (Thaleichthys pacificus) using the best available science per the requirements of the Endangered Species Act.[17][18]

In Canada, the Central Pacific Coast and Fraser River populations were classified as endangered by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in 2011.[12] At that time, the Nass / Skeena Rivers population was given threatened status, but this was downgraded to Special Concern status when the Nass / Skeena Rivers population was individually reassessed by COSEWIC in 2013.[19] As of May 2023, a decision is pending on the listing of these populations under Schedule 1 of the Species at Risk Act.[20]

Overall, the species faces multiple threats, including overharvest, pollution, loss of freshwater spawning habitat due to logging, diversion and dam construction and climate change.[1][2] Canadian spawning runs have been severely depleted compared to historic levels,[19] while abrupt declines were reported in the Columbia, Fraser and Klinaklini rivers in 1994.[1]

References

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Eulachon

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The eulachon (Thaleichthys pacificus), commonly known as the candlefish or hooligan, is a small anadromous smelt belonging to the family Osmeridae, inhabiting coastal marine waters of the northeastern from to . This species typically reaches a length of up to 10 inches (25 cm), spending over 95% of its life in saltwater environments at depths ranging from nearshore to 300 meters or more, before returning to freshwater rivers for semelparous spawning in spring, where adults die after a single reproductive event. Renowned for its high oil content, which historically enabled of the to render eulachon grease for food preservation, , and , as well as to burn as candles—earning its "candlefish" moniker—the species has served as a cultural keystone, often termed the "salvation fish" for sustaining communities through seasonal abundance after winter scarcity. Ecologically, eulachon function as a key , supporting predators including seabirds, marine mammals, and larger , while their spawning runs in rivers like the Columbia, Fraser, and Nass provide critical nutrient pulses to riparian ecosystems via post-spawning carcasses. Although eulachon populations exhibit natural fluctuations, with historical records documenting cyclic booms and busts, the southern distinct population segment—from the south to —has experienced persistent declines since the 1990s, leading to its listing as threatened under the U.S. Endangered Species Act in 2010, attributed to factors such as alteration, , and possibly climate-driven changes in ocean conditions, though northern runs in and parts of remain more robust. Conservation efforts focus on monitoring spawning returns, reducing impacts, and restoring river s, reflecting the ' resilience alongside ongoing vulnerabilities in specific regions.

Taxonomy and Nomenclature

Scientific Classification

The eulachon (Thaleichthys pacificus Richardson, 1836) belongs to the family Osmeridae, comprising the true smelts, and represents the sole within its monotypic Thaleichthys, a name derived from Greek roots denoting "rich" or "oily" fish in reference to its high fat content. This classification places it among the osmeriforms, a group of small, primarily anadromous fishes characterized by certain osteological and morphological traits, as outlined in phylogenetic analyses of the Osmeroidei superfamily.
Taxonomic RankClassification
KingdomAnimalia
PhylumChordata
ClassActinopterygii
OrderOsmeriformes
FamilyOsmeridae
GenusThaleichthys
SpeciesT. pacificus
This hierarchy reflects the current consensus in ichthyological databases, with no recognized subspecies or significant taxonomic revisions since the original description by John Richardson in 1836 based on specimens from the Pacific Northwest. The placement in Osmeriformes is supported by morphological phylogenies emphasizing features like the structure of the upper jaw and adipose fin, though molecular studies continue to refine relationships within the Protacanthopterygii superorder.

Etymology and Common Names

The name eulachon derives from , a trade language of the Pacific Northwest , ultimately tracing to spoken by groups such as the Clatsop, a Lower Chinook division along the . Variations include oolichan, ooligan, hooligan, and ulâ'qan, reflecting phonetic adaptations in Indigenous dialects and European transliterations during early contact. Indigenous communities historically referred to the fish as a "salvation fish" due to its nutritional importance during spring runs, providing high-fat sustenance after winter. The binomial scientific name Thaleichthys pacificus originates from Greek roots: thaleia or thaleichthys denoting "rich" or "luxurious fish," alluding to the species' high oil content and abundance, combined with ichthys for "fish" and pacificus indicating its distribution. Among English common names, "candlefish" stems from the fish's extreme fat content during spawning—up to 15% of body weight—which historically allowed dried specimens, threaded with a wick, to be burned as candles by and early settlers. Other regional names include "hooligan" in and "smelt" more broadly, though the latter applies to the Osmeridae family generally; "fathom fish" appears less commonly in historical accounts.

Description

Morphology and Anatomy


The eulachon (Thaleichthys pacificus) has an elongated body with a laterally compressed cross-section and body depth comprising 15-20% of total length. Adults typically reach 20 cm in total length, with a maximum of 34 cm. Coloration exhibits , with the back and head brown to blue, sides silvery white, and ventral surface white; fine, sparse speckling occurs on the back. In saltwater, the body appears blue-silver, shifting to gray-brown and green in freshwater during spawning. The flesh contains high levels of oil, contributing to its historical use as a when dried. The head features a large , with the extending to or past the rear margin of the eye, and prominent canine-like teeth on the , which are absent by spawning time. covers bear obvious circular grooves, a distinguishing trait among smelts. The species has 65-72 vertebrae. Fin structure includes no dorsal or anal spines; the dorsal fin has 10-13 soft rays and originates well posterior to the pelvic fin insertion; the anal fin bears 18-23 soft rays; a sickle-shaped adipose fin is present aft of the dorsal. Fins are transparent, with pectoral and caudal often dusky; they lack markings. Paired pectoral and pelvic fins are longer in males than females. Sexual dimorphism is pronounced during spawning: males develop a raised midlateral , well-developed tubercles on the head, body scales along the , and fins, imparting a rough texture; females are smaller, smoother, shinier, with poorly developed or absent tubercles.

Size, Growth, and Reproduction

Adult eulachon typically measure 15 to 25 centimeters in total , with a maximum recorded of 34 centimeters. Mature individuals commonly weigh around 40 to 90 grams, though weights up to 2.5 ounces (approximately 70 grams) have been reported for spawning adults. Eulachon exhibit rapid early growth, with larvae increasing from 3-4 millimeters to 30-35 millimeters over 18-20 weeks post-hatching in freshwater before migrating to the . In marine environments, they rear for 3 to 5 years, reaching at lengths of about 15.5 centimeters and ages of 2 to 5 years, though most spawn at age 3. Growth continues modestly with age, as age-2 fish average 18-20 centimeters and 40-58 grams, while age-5 individuals reach 22-23 centimeters and 80-90 grams. Eulachon are semelparous anadromous fish that migrate to freshwater rivers to spawn once, typically dying shortly thereafter. Females produce 7,000 to 60,000 eggs, averaging around 30,000, with individual eggs approximately 1 millimeter in diameter; these demersal eggs adhere to fine sediments and incubate for 30 to 40 days before hatching. Spawning occurs in spring in lower river reaches, with and eggs released simultaneously over the substrate in a broadcast manner. A small fraction of individuals may be iteroparous, surviving to spawn again, but this is rare.

Distribution and Habitat

Geographic Range

The eulachon (Thaleichthys pacificus), an anadromous smelt, inhabits coastal marine waters of the northeastern , extending from in northward to the , including areas west of Saint Matthew Island and Kuskokwim Bay. This range encompasses nearshore environments off the coasts of , , Washington, , and , where adults reside for over 95% of their life cycle at depths up to approximately 183 meters (600 feet). For spawning, eulachon migrate into the lower reaches of coastal rivers characterized by strong spring freshets from or glacial runoff, with documented sites from the Mad River in northward through major systems in the and , such as those in , the Copper River Delta, and rivers draining to near Nome. These migrations typically occur in rivers with water temperatures between 4.4°C and 7.8°C, pea-sized gravel substrates, and moderate velocities, though run timing and success vary annually across the range due to environmental factors like river flow and temperature. The species' distribution includes distinct population segments, with the southern DPS—encompassing populations from to —federally listed as threatened under the U.S. Endangered Species Act since 2010, reflecting localized declines amid the broader range. Northern populations, extending into , remain more abundant but exhibit erratic run patterns influenced by oceanic conditions.

Preferred Environments

Eulachon (Thaleichthys pacificus) primarily occupy marine environments along the northeastern Pacific coast, favoring nearshore coastal waters and inlets where adults aggregate in schools at moderate depths of 20–200 meters, though they have been recorded as deep as 625 meters. These fish spend more than 95% of their life cycle in saltwater habitats, exhibiting limited tolerance for prolonged freshwater residence outside of spawning periods. Spawning occurs exclusively in freshwater, with adults migrating into the lower reaches of medium to large coastal rivers featuring clean substrates, flowing pools, and gravel runs suitable for egg and incubation. Preferred spawning sites are those with spring snowmelt-driven freshets that maintain water s around 5–10°C, provide sufficient oxygen levels, and generate high flows to scour substrates and facilitate larval drift downstream. These conditions ensure egg survival rates, as eulachon eggs require well-oxygenated, unembedded for development over 15–30 days, depending on . Estuaries function as transitional rearing grounds for post-larval juveniles, offering intermediate , abundant planktonic , and protection from oceanic predators during the critical outmigration phase. Juvenels rapidly adapt to increasing salinity as they move seaward, with estuary residence typically lasting days to weeks before full marine integration. Eulachon exhibit sensitivity to habitat alterations such as , which clogs spawning gravel, or altered flow regimes from that disrupt larval transport and temperature cues.

Ecology and Behavior

Life Cycle

Eulachon (Thaleichthys pacificus) exhibit an anadromous life cycle, hatching in freshwater, migrating to the for growth, and returning to natal rivers to spawn. Adults typically reach maturity at ages 2–5 years, with most spawning at age 3, after spending 2–7 years in marine environments depending on conditions. The is predominantly semelparous, with most individuals dying shortly after a single spawning event, as evidenced by trace element analyses showing no significant repeat spawners and observations of post-spawn mortality including substantial tooth loss and carcass decay. A small proportion may survive to spawn a second time in their fourth year, but iteroparity is rare and unconfirmed in most populations. Spawning occurs in the lower reaches of coastal rivers from to , typically between December and June when water s range from 0°C to 10°C. Females deposit eggs on substrates of coarse sand or fine in areas with moderate water flow, often in tidal-influenced zones; eggs are demersal, adhesive, and approximately 1 mm in diameter, attaching to particles. varies from 7,000 to 60,000 eggs per female, with broadcast spawning where males release over eggs in shallow, flowing water. Incubation lasts 30–40 days, influenced by , after which larvae hatch and immediately drift downstream to estuarine and marine waters, minimizing freshwater residence to avoid predation and osmotic stress. Larval eulachon are pelagic upon reaching saltwater, feeding on before undergoing into juveniles that resemble adults. residence supports rapid growth to adult sizes of 172–185 mm (fork length), fueled by high content that enables energy-intensive migrations. Migration upstream for spawning is triggered by environmental cues like river flow and , with adults traveling hundreds of kilometers; males often precede females and outnumber them in runs. Post-spawning mortality results from exhaustion, injury during ascent, and physiological stress, contributing to transfer from to river ecosystems akin to Pacific salmon.

Diet, Predation, and Migration

Eulachon (Thaleichthys pacificus) primarily consume planktonic organisms during their marine phase, with juveniles feeding on copepods and mysids, while adults target euphausiid shrimp (commonly known as ) and other small crustaceans such as amphipods. Their diet shifts little upon entering freshwater for spawning, as adults cease feeding during this period to focus energy on reproduction. As a high-lipid , eulachon serve as prey for diverse predators across marine, estuarine, and riverine environments. In the ocean, they are consumed by marine mammals including Steller sea lions (Eumetopias jubatus), harbor seals (Phoca vitulina), and occasionally whales and dolphins; seabirds such as cormorants, mergansers, and gulls also target them. During spawning runs in rivers, aggregations attract intensified predation from avian species like bald eagles (Haliaeetus leucocephalus), piscivorous fish such as (Acipenser transmontanus), and pinnipeds that enter estuaries. These interactions peak in spring, with predators congregating at river mouths, potentially influencing local eulachon run success through elevated mortality rates. Eulachon exhibit anadromous migration, residing in nearshore Pacific waters for 3–5 years before returning to natal rivers to spawn semelparously, after which adults die. Spawning migrations typically initiate when river temperatures range from 0°C to 10°C, occurring between and depending on latitude, with peaks in February–March for southern populations like those in the and later (March–May) in northern systems such as rivers. Juveniles hatch 20–40 days post-fertilization and rapidly outmigrate to the as larvae, drifting downstream within weeks to avoid riverine predation and access marine . Migration timing and success vary by stock, influenced by conditions, river flow, and temperature, with acoustic telemetry studies in the indicating travel speeds of 0.5–2 km/h and residence times of days to weeks in lower reaches.

Human Interactions

Cultural and Indigenous Significance

Eulachon (Thaleichthys pacificus), referred to as ooligan or oolichan in various Indigenous languages, serves as a cultural for First Nations communities along the coast, integral to sustenance, ceremonies, and social structures. Archaeological evidence from northern Northwest Coast sites, including faunal remains and processing artifacts dated to pre-contact periods, demonstrates its long-standing role in Indigenous fisheries, with intensified harvest during seasonal runs. Ethnographic highlight its use in feasts, , and medicinal applications, underscoring a balanced environmental relationship facilitated by . Among the Nisga'a Nation, eulachon is known as the "saviour fish" for providing critical high-fat nutrition at the end of winter, enabling survival and cultural continuity through grease rendering—a process yielding a preserved oil used in food, lighting, and exchange. The Nuxalk Nation similarly relies on eulachon runs for community cohesion, with historical practices involving large-scale fermentation and rendering in "stink boxes" to produce ooligan grease, a staple fat source documented in oral traditions and recent revivals after periods of scarcity. For Coastal Salish peoples, the fish's oil facilitated food preservation and trade networks, influencing intergenerational knowledge transmission and seasonal migrations to harvest sites. These practices extend to spiritual dimensions, with eulachon embodying resilience and abundance in Indigenous cosmologies, as evidenced by ceremonies commemorating runs and declines, such as the 2007 Bella Coola feast mourning population reductions while affirming cultural ties. Government assessments affirm its enduring cultural value, noting dependencies in First Nations for traditional economies predating European contact. Despite contemporary challenges, efforts like Nuxalk-led monitoring integrate ancestral harvesting techniques with ecological stewardship to sustain this heritage.

Historical and Traditional Uses

of the , including and , have harvested eulachon (Thaleichthys pacificus) for millennia, particularly during annual spawning runs in spring rivers. These runs provided a critical food source after winter, earning the fish the name "salvation fish" among groups like the , as their high fat content—up to 20% by weight—offered essential calories and nutrients. Harvesting involved communal netting at river mouths, followed by processing through , , or rendering into , with families camping for weeks to maximize yields. The primary traditional product was ooligan grease, extracted by fermenting whole in pits or containers for several days to break down tissues, then in to separate the , which was skimmed, strained, and stored in cedar boxes or bags. This grease served as a high-energy for dried meats, berries, and other foods, providing essential fatty acids and vitamins, and was nutritionally dense with documented use sustaining coastal and interior populations. Due to its oiliness, dried eulachon could be lit as candles or torches, a practice giving rise to the common name "candlefish," particularly among and other groups for nighttime illumination. Eulachon grease was a vital item, exchanged inland via extensive networks reaching and , where it functioned as a , for ailments like conditions, and ceremonial . Archaeological evidence and oral histories indicate pre-contact fisheries emphasized sustainable practices, with runs supporting social gatherings and cultural rituals tied to seasonal abundance. By the mid-19th century, European observers noted continued indigenous processing without salt, adapting eulachon into smoked or rendered forms for storage and .

Commercial and Economic Exploitation

Commercial fisheries for eulachon (Thaleichthys pacificus) historically targeted the species for its high oil content, approximately 18-20% of wet weight, which was rendered into grease for food preservation, trade, and bait, contributing to local economies in the Pacific Northwest and Alaska. In Canada, early 20th-century harvests in the Skeena River area ranged from 17.3 tonnes in 1924 to varying annual totals through 1946, primarily for oil and smoked products processed at sites like Port Essington on the Nass River. Columbia River commercial landings in the U.S. Pacific Northwest peaked in the early 20th century but declined sharply by the mid-1990s, prompting management restrictions. Directed commercial harvests have since become limited due to population declines, with many fisheries closed or restricted to protect spawning stocks. In the , Canada, the commercial fishery was closed in 1997 following increased effort and low abundance, reopening only occasionally for test fisheries. U.S. West Coast fisheries, including , recorded negligible landings since 1990 (less than 30 pounds total in two instances), while Washington and reported harvest rates of 0.03-3.03% of estimated runs from 2013-2022, encompassing non-treaty commercial, tribal, and recreational takes under joint management plans. In , the Northern District of supports an active dipnet fishery targeting Susitna River returns, with harvests beginning at 300 pounds in 1978 and expanding to commercial scales, though exact recent yields vary with abundance and management guidelines. Other Alaskan rivers, such as the Unuk, have seen closures since 2001 amid stock collapses. Economic exploitation centers on eulachon (grease), valued for its nutritional and historically traded at prices up to $75 per in areas like the Chilkat River, supporting Indigenous and local markets but diminishing with regulatory limits. Bycatch in groundfish and shrimp trawls remains a concern, with U.S. West Coast estimates from observer data indicating incidental mortality, though not a primary economic harvest vector. Overall, commercial activity generates limited revenue today compared to historical peaks, overshadowed by conservation priorities for the threatened southern distinct segment.

Conservation and Management

Eulachon populations across their range have undergone substantial declines since the mid-20th century, with coastwide reductions reported since the early 1990s, though some northern stocks exhibit variability and partial recoveries. The Southern Distinct Population Segment (DPS), spanning U.S. rivers from the Klamath to the Columbia, has shown persistently low abundances, with no recovery criteria met as of the 2022 review; spawning stock biomass in the Columbia River dropped from a mean of 97.9 million individuals (2011–2015) to 40.2 million (2016–2021). In the Klamath River, returns remain minimal, with observations of only small numbers (maximum 2 per night) since 2014. Canadian populations, particularly the Fraser River stock, have experienced severe contractions, with spawning biomass falling 98% from 1998 to 2008, reaching a historic low of 10 tonnes against a long-term average of approximately 1,000 tonnes. More recent data indicate a modest increase in spawning stock biomass, from 2.8 million (2011–2015) to 4.9 million (2016–2021), attributed to strong returns in 2018 and 2020, though overall levels remain depressed. Central Pacific Coast rivers in , such as and Kemano, have seen over 90% declines in some cases over 15-year periods ending around 2008, leading to near extirpation in several systems, while modest returns persist in rivers like Kingcome and Klinaklini. Northern stocks, including Nass and Skeena rivers, display relative stability compared to southern populations but still reflect long-term reductions, with Nass River catch per unit effort declining 48% over three generations and run sizes estimated at less than 10% of 19th-century levels (from ~2,100 tonnes to ~200 tonnes annually). Recoveries have occurred sporadically, such as in Skeena and Kemano post-1994, and increased marine abundances off and during 2000–2002, but these do not indicate sustained reversal of the broader downward trajectory. Long-term projections for the Southern DPS forecast further declines of 26.4% to 35.7% by 2050, despite short-term optimism tied to improved ocean conditions. Historical records show cyclical fluctuations, including recoveries in the between 1835 and 1865, underscoring the species' potential resilience amid episodic abundance.

Threats and Causal Factors

The southern Distinct Population Segment (DPS) of eulachon (Thaleichthys pacificus) experienced an abrupt and persistent decline in abundance across its range starting in the late 1980s to early 1990s, with escapement indices dropping by over 90% in major rivers like the Columbia and Fraser compared to historical peaks exceeding 10 million individuals. While the precise causal mechanisms remain incompletely understood due to the species' complex anadromous life history spanning estuarine, riverine, and marine environments, analyses by the National Marine Fisheries Service (NMFS) Biological Review Team (BRT) identify a combination of anthropogenic habitat alterations and marine ecosystem shifts as primary drivers. In freshwater spawning habitats, the destruction, modification, or curtailment of riverine access constitutes a leading threat, particularly from hydroelectric dams and water diversions that block migration routes and fragment spawning grounds; for instance, the Federal Power System has been linked to reduced juvenile outmigration survival and altered river flows, exacerbating vulnerability during the semelparous spawning runs. degradation from , agricultural pollutants, and industrial discharges further impairs egg and larval viability, with elevated and contaminants documented in key rivers like the Fraser, where pervasive anthropogenic modifications correlate with sustained low returns. Overutilization through historical commercial fisheries, which harvested millions annually in the mid-20th century before moratoria, compounded these pressures, though current indigenous and recreational harvests are managed under quotas to minimize impacts. Marine-phase threats predominate in BRT assessments, with climate-driven changes in ocean conditions—such as warming waters, altered , and reduced prey availability—rated as the most severe factor affecting juvenile growth and survival during the extended oceanic residency phase, which spans 3–5 years before maturation. These shifts, evident in regime changes like the 1990s transition, have been associated with broader declines and increased predation pressure from species like harbor seals and piscivorous fish, though quantitative attribution remains challenging without long-term tagging data. in commercial trawl fisheries targeting groundfish and , estimated at thousands of tons annually in some years, adds mortality, particularly to immature eulachon, despite regulatory reductions. Secondary factors, including disease outbreaks and competition in altered estuaries, contribute incrementally but lack strong empirical linkages to the observed collapse.

Regulatory Status and Efforts

The southern distinct population segment (DPS) of eulachon (Thaleichthys pacificus), encompassing populations from the in northward to the in , was listed as threatened under the U.S. Endangered Species Act (ESA) by NOAA Fisheries effective March 16, 2010, following a determination that substantial declines in abundance and degradation warranted protection. Critical for this DPS, including key riverine spawning and rearing areas such as the Basin, was designated on February 3, 2011, to address ongoing threats like altered freshwater flows and sediment contamination. The northern DPS, ranging from the U.S.- border to , was not listed, as available data indicated relatively stable populations in that region. In , the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) designated eulachon populations in the Nass River, Central Pacific Coast, and designatable units as endangered in February 2018, citing severe declines exceeding 90% over three generations due to factors including and impacts, while other units were assessed as threatened or of special concern. These assessments informed recommendations for listing under Canada's Species at Risk Act (SARA), with implementing precautionary management measures, though formal SARA protections remained under review as of 2022. Harvest regulations in the U.S. are governed by state-tribal agreements, such as the Washington- Eulachon Management Plan updated in 2023, which establishes run-size forecasts, allowable harvest rates (typically capped at 10-20% of forecasted returns to protect spawners), and in-season closures if abundance falls below thresholds to minimize impacts on the ESA-listed southern DPS. In the , commercial and recreational harvests are jointly regulated by Washington and under the Columbia River Compact, with seasons often limited to short windows and gear restrictions like dip nets to sustain tribal subsistence needs while adhering to ESA consultation requirements. permits subsistence eulachon harvest using dip nets from May 1 to June 30, with total annual limits not exceeding 200 tons in monitored fisheries, and certain rivers like the Unuk closed to non-subsistence users under federal subsistence regulations. in West Coast groundfish fisheries is minimized through real-time monitoring and release protocols, as documented in annual reports showing estimated incidental take below ESA incidental take statement levels. Conservation efforts include NOAA's 2013 Federal Recovery Outline, which prioritizes actions like habitat restoration in degraded estuaries, improved passage at dams, and long-term monitoring of spawning runs via aerial surveys and genetic stock assessments to track recovery progress. A 2022 five-year status review by NOAA reaffirmed the threatened classification, noting persistent low returns in major rivers like the Columbia (averaging under 1 million spawners annually since 2010) but highlighting stabilizing trends in some indices and knowledge gaps in marine survival drivers. Collaborative initiatives, such as those by the Northwest Power and Conservation , fund research into eulachon early life history and , while tribal co-management emphasizes culturally informed protections alongside empirical data on population viability.

Debates on Decline and Recovery

Populations of the southern Distinct Population Segment (DPS) of eulachon (Thaleichthys pacificus) experienced an abrupt range-wide decline beginning around 1994, with spawning stock biomass (SSB) in the dropping from peaks exceeding 97 million individuals (2011–2015 average) to lows of 4.1 million in 2018 and a 2016–2021 average of 40 million. Similar trends occurred in other rivers, leading to a U.S. Endangered Species Act (ESA) listing as threatened in March 2010, though Fraser River SSB showed partial rebound to 13.6 million in 2020. Debates on decline causes center on the relative roles of marine environmental factors versus anthropogenic freshwater and impacts, with empirical evidence pointing to conditions as the dominant driver. NOAA's Biological Review Team (BRT) ranks climate-influenced changes—such as reduced , warmer sea surface temperatures, and prey scarcity (e.g., copepods and euphausiids)—as the highest , correlating with poor marine survival during events like the 2013–2016 "Blob" marine heatwave, which may explain sharp Columbia SSB drops in 2017–2018. Proponents of this view note synchronous declines across systems with varying human impacts, including the undammed , suggesting broad-scale oceanic forcing over localized habitat degradation like reducing spring freshets by 41% in the Columbia Basin, which could impair larval outmigration but lacks causal isolation. Counterarguments emphasize (e.g., 19.8 million eulachon in 2019 trawls) and predation as exacerbating factors, though reductions via bycatch reduction devices (BRDs) achieving 66–88% lower incidental catch post-2003 indicate these are mitigable but not primary. Uncertainties persist in quantifying escape mortality and hypoxia tolerance, complicating attribution. Recovery debates focus on the feasibility of actions amid persistent oceanic variability, with no southern DPS subpopulation meeting high ESA recovery criteria (e.g., sustained 229.5 million Columbia spawners for 24 of 30 years) despite occasional low-threshold compliance. Efforts include mitigation (e.g., light-based reductions of 90.5% in tests) and Federal Columbia River Power System (FCRPS) flow adjustments for larval transport, but efficacy is questioned due to flood control constraints limiting freshet restoration and the dominance of uncontrollable marine factors. Stakeholders debate prioritizing monitoring (e.g., SSB via egg/larval surveys) and habitat enhancements over broader climate adaptations, given inadequate regulatory responses to per IPCC assessments, with short-term optimism tied to favorable regimes but long-term from trend projections. Lack of robust population models hinders evaluation, underscoring calls for eDNA and hydroacoustic tools to resolve uncertainties.

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