Atlantic salmon (Salmo salar) COSEWIC assessment and status report: chapter 2

Executive Summary

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COSEWIC
Executive Summary

Atlantic Salmon
Salmo salar

Nunavik population, Labrador population, Northeast Newfoundland population, South Newfoundland population, Southwest Newfoundland population, Northwest Newfoundland population, Quebec Eastern North Shore population, Quebec Western North Shore population, Anticosti Island population, Inner St. Lawrence population, Lake Ontario population, Gaspé-Southern Gulf of St. Lawrence population, Eastern Cape Breton population, Nova Scotia Southern Upland population, Inner Bay of Fundy population, Outer Bay of Fundy population

Wildlife Species Information

The Atlantic Salmon (Salmo salar) is a member of the family Salmonidae. This species has a fusiform body shape and matures at sizes ranging from 10 to 100+ cm. Atlantic Salmon exhibit plastic life histories and may have multiple reproductive and migratory phenotypes within a population, including freshwater resident and oceanic migrant forms. All phenotypes reproduce in fresh water. The oceanic migrant (anadromous) form is the best known phenotype, and with the exception of the extinct Lake Ontario population, is the only form considered in this report. Juveniles spend 1-8 years in fresh water, then migrate to the North Atlantic for 1-4 years, and then return to fresh water to reproduce. Demographically functional units tend to be at the watershed scale, but population subdivision may occur within watersheds. The Canadian range of this species was subdivided into 16 designatable units (DUs) based on genetic data and broad patterns in life history variation, environmental variables, and geographic separation.

Distribution

Atlantic Salmon originally occurred in every country whose rivers flow into the North Atlantic Ocean and Baltic Sea. In Europe, the range of the Atlantic Salmon extended southward from northern Norway and Russia along the Atlantic coastal drainage to Northern Portugal, including rivers in both France and Spain. In North America, the range of the anadromous Atlantic Salmon was northward from the Hudson River drainage in New York State, to outer Ungava Bay and eastern Hudson Bay in Quebec. The Canadian range is roughly one-third the area of the total global range, and extends northward from the St. Croix River (at the border with Maine, U.S.A.) to the outer Ungava Bay and eastern Hudson Bay in Quebec. Recent estimates suggest Canada has at least 700 rivers which either currently support Atlantic Salmon populations, or did so in the past.

Habitat

Rivers with Atlantic Salmon are generally clear, cool and well oxygenated, with low to moderate gradient, and possessing bottom substrates of gravel, cobble and boulder. Freshwater habitat is considered a limiting resource to freshwater production and is used to set conservation requirements for Canadian rivers. There have been substantial declines in habitat quantity and quality in the southern portion of the species’ Canadian range. This loss of freshwater habitat may be an important risk factor for declining abundance in several southern DUs. Trends in the quality and quantity of marine habitat are not well understood, but large-scale changes in ocean ecosystems may be adversely affecting Atlantic Salmon across their range.

Biology

Atlantic Salmon is an iteroparous species that returns to natal rivers to spawn with a high degree of fidelity, despite completing ocean-scale migrations. Spawners returning to rivers are comprised of varying proportions of ‘maiden fish’ (those spawning for the first time) and ‘repeat spawners’. Maiden salmon consist of smaller fish that return to spawn after one winter at sea (1SW or Grilse) and larger fish that return after two or more winters at sea (MSW). Some river populations include fish that return to spawn after only a few months at sea. During any breeding season, there can be varying proportions of maiden, consecutive and alternate spawners in the spawning runs. Collectively over the entire range in North America, adult Atlantic Salmon return to rivers from feeding and staging areas in the sea mainly between May and November, but some runs can begin as early as March and April. In general, run timing varies by river, sea age, year, and hydrological conditions. Deposition of eggs in gravel nests, by oviparous mothers, usually occurs in October and November in gravel-bottomed riffle areas of streams or groundwater seepage on shoals in lakes. Fertilization of eggs can involve both adult males and sexually mature precocious males. Mating behaviour typically entails multiple males of several life history types competing aggressively for access to multiple females. This frequently leads to multiple paternity for a given female’s offspring. Spawned-out or spent adult salmon (kelts) either return to sea immediately after spawning or remain in fresh water until the following spring. Eggs incubate in the spawning nests over the winter months and hatching usually begins in April. The hatchlings (alevins) remain in the gravel for several weeks living off large yolk sacs. Upon emergence from the gravel in late May – early June, the yolk sac is absorbed and the free-swimming young fish (parr) begin active feeding. Parr rear in fluvial and lacustrine habitats for one to eight years following which they undergo behavioural and physiological transformations and migrate to sea as smolt.

Population Sizes and Trends

Abundances and trends were highly variable across the 16 DUs, with estimated abundances ranging from estimates of <1000 to 235,874. Although the total Canadian population appears to be relatively stable over the last three generations, this apparent recent stability masks a significant historical decline, regional variability, and a general, although often statistically non-significant decline in abundance for 14 of 16 DUs during the last three generations. The stability of the total Canadian population is driven primarily by estimated increases in abundance in Labrador, although data from this region are relatively limited and there is considerable uncertainty in the resulting abundance estimates and trends. Several of the southern DUs (e.g. DU 16: Outer Bay of Fundy; DU 15: Inner Bay of Fundy; and DU 14: Southern Upland) are at or near their lowest abundance on record. It is also important to point out that several historical analyses in the literature that go back more than four generations show a substantial decline in Canadian abundance. The three-generation analysis completed herein should be considered within this longer-term context.

Threats and Limiting Factors

Threats to Atlantic Salmon include, but are not limited to, climate change, changes to ocean ecosystems, fishing (commercial, subsistence, recreational, and illegal), dams and obstructions in freshwater, agriculture, urbanization, acidification, aquaculture, and invasive species. The relative contributions of these factors to declines remain unclear and vary among populations. Generally, freshwater threats are less significant in the northern portions of the range. Recent broad-scale declines in marine survival suggest that the most substantial threat(s) to the species are in the marine environment, although in some southern areas, freshwater habitat degradation and fish passage issues are expected to limit population growth if marine survival improves.

Special Significance

Atlantic Salmon are contributors to both freshwater and marine ecology, moving nutrients between ecosystems as migrants, and linking energy flow as prey and as predators within ecosystems. They are traditionally used by (i) over 49 First Nations and Aboriginal organizations, (ii) commercial fisheries and (iii) recreational fisheries. They are also the subjects of local art, science and education, and symbols of heritage and health to peoples of Canada.

Existing Protection, Status, and Ranks

The Atlantic Salmon is currently designated or ranked with several international and national bodies. In the United States of America, populations in Maine have Endangered status under the U.S. Endangered Species Act. In April 2006, the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assessed the Inner Bay of Fundy population as Endangered and the Lake Ontario population as Extirpated. The Atlantic Salmon, Inner Bay of Fundy population is currently listed as Endangered under Canada’s Species at Risk Act (SARA).

Aboriginal Traditional Knowledge

Aboriginal traditional knowledge (ATK) is considered a critical component for status assessments for endangered wildlife (COSEWIC). Atlantic Salmon, in particular, is a species for which considerable ATK exists. COSEWIC’s ATK Subcommittee initiated work with Aboriginal communities in eastern Canada to gather ATK for the COSEWIC Status Report on Atlantic Salmon in 2008. The Aboriginal communities indicated, through the ATK Subcommittee members, that ATK was available and expressed a willingness to share the information. However, challenges arose in developing a satisfactory approach for the collection of this ATK. As such, ATK is not available at this time for use in the COSEWIC Status Report for this species. The ATK Subcommittee and COSEWIC will continue to work on gathering ATK on Atlantic Salmon for inclusion in a future report.

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