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COSEWIC assessment and status report on the Atlantic Salmon (Inner Bay of Fundy populations) in Canada

Technical Summary

 

Salmo salar      Saumon atlantique
Atlantic salmon
Inner Bay of Fundy populations      Populations de l’intérieur de la baie de Fundy
Range of Occurrence in Canada: Inner Bay of Fundy

Extent and Area Information

·        Extent of occurrence (EO)(km²)      About 40,000 km² freshwater; unknown marine
            area measurements from DFO regional map of iBoF watersheds
·        Specify trend in EO      Unknown
·        Are there extreme fluctuations in EO?      Unknown
·        Area of occupancy (AO) (km²)      Unknown, but > 9km² potential freshwater occupancy; unknown marine
            Amiro (2003) estimate of potential productive habitat in 22 rivers
·        Specify trend in AO      Declining in freshwater due to local extirpations
·        Are there extreme fluctuations in AO?      Possibly (due to local     extirpation/colonization)
·        Number of known or inferred current locations      19 rivers
            juvenile presence (Figure 11)
·        Specify trend in #      Declining
·        Are there extreme fluctuations in number of locations?      Unknown
·        Specify trend in area, extent or quality of habitat      Freshwater habitat believed stable, while marine habitat possibly declining over past 3 generations

Population Information

·        Generation time (average freshwater plus marine time in years to first spawning)      3.7 years
·        Number of mature individuals      < 100 (estimated)
·        Total population trend:      Rapidly declining
·        % decline over the last 3 generations (11 years; to 2002)      > 94% (this is the lowest 90% confidence limit for the healthiest index river)
·        declining trend did not change in 2003 (Gibson et al. 2004)
·        Are there extreme fluctuations in number of mature individuals?
      No
·        Is the total population severely fragmented?      Yes
·        Specify trend in number of populations      Declining
·        Are there extreme fluctuations in number of populations?      Unlikely
·        List populations with number of mature individuals in each:
Two index rivers:
      - Big Salmon river (2002): 55 (80% Bayesian Credible Interval = 18-133)
      - Stewiacke river (2001): 2 (80% BCI = 2-4)

Threats (actual or imminent threats to populations or habitats)

Leading marine considerations: interactions with farmed and hatchery salmon (competition with escapees; parasite and disease epidemics), ecological community shifts (increased predation by native species; lack of forage species), depressed population phenomena (lack of recruits to form effective shoals), environmental shifts (regime shift depressing ocean productivity; altered migration routes leading to depressed survival), fisheries (excessive illegal and/or incidental catch), and the possibility of cumulative interactions among these or more factors. 

Leading freshwater considerations: interbreeding and competition with escaped farm fish, depressed population phenomena (abnormal behaviour due to low abundance; inbreeding depression), changes in environmental conditions (climate changes leading to premature smolt emigration and decreased freshwater productivity; atmospheric changes increasing ultraviolet radiation; increased contaminant concentrations), historical reduction in habitat quality.

Rescue Effect (immigration from an outside source)      Not applicable

·        Status of outside population(s)?
The two nearest Canadian regions, outer Bay of Fundy and Scotian Coast, have severely depressed populations. Calculations of current decline rates exceed COSEWIC criteria for Endangered.  The nearest US region is Maine where populations are Endangered (ESA 2001).
Since outside populations are a different DU, they cannot rescue the iBoF.
·        Is immigration known or possible?      Unlikely (few fish)
·        Would immigrants be adapted to survive in Canada?      Unlikely (local adaptations)
·        Is there sufficient habitat for immigrants in Canada?      Likely
·        Is rescue from outside populations likely?      No - different DU

Quantitative Analysis      Rudimentary calculation

Simplified calculations from current decline rates (3-generation) and current population size estimates (2003) project extinction in less than 15 years.

Current Status
COSEWIC: Endangered (2001), Endangered (2006)
SARA: Endangered (2003)

Status and Reasons for Designation

Status : Endangered
Alpha-numeric code :  A2bc; C2a(i,ii); D1
Reason for Designation: These salmon represent a unique Canadian endemic; their entire biological distribution exists within Canada. Adult numbers are estimated to have declined by more than 95% in 30 years, and most rivers no longer have either adults or juveniles.  In 2003, fewer than 100 adults are estimated to have returned to the 32 rivers known to have historically contained the species. There is no likelihood of rescue, as neighbouring regions harbour severely depressed, genetically dissimilar populations. The reasons for the collapse in adult abundances are not well understood. Reduced survival from smolt to adulthood in marine waters is thought to be a key factor. There are many possible causes of this increased mortality, including ecological community shifts; ecological / genetic interactions with farmed and hatchery Atlantic salmon; environmental shifts; and fisheries (illegal or incidental catch). Threats to the species in the freshwater environment are thought to be historical and contemporary in nature. Historical threats include loss and degradation of habitat (attributable to the construction of barriers to migration and logging); contemporary threats may include interbreeding with escaped farmed fish and environmental change (warmer temperatures, contaminants).

Applicability of Criteria

Criterion A: Meets Endangered, A2b (population declines > 50% over the past 3 generations, using an index of abundance appropriate for the taxon, where the reduction or its causes may not have ceased or many not be understood). In the two main index rivers, percent decline is > 94.1% over 3 generations (11 years) in the Big Salmon River and > 99.0% over 3 generations (11 years) in the Stewiacke River. These decline estimates are at a 90% level of confidence, obtained using several indices of abundance (maximum likelihood models incorporating recreational fishing catch and effort data, redd counts, electrofishing, and mark-recapture). Also, meets Endangered, A2c (population declines > 50% over the past 3 generations, where the reduction or its causes may not have ceased or may not be understood, and a decline in area of occupancy). A decline in freshwater area of occupancy due to local extirpations has been noted. 97% of historical spawning rivers surveyed in 2002 contained no fry, indicating no spawning there by the Inner Bay of Fundy Populations of Atlantic salmon in fall 2001.
Criterion B: Although the Area of Occupancy is almost certainly less than 500 km², the Inner Bay of Fundy populations of Atlantic salmon are known to exist at more than 10 locations, and extreme fluctuations have not been reported for extent of occurrence, area of occupancy, number of locations or populations, or number of mature individuals.
Criterion C: Meets Endangered, C2a(i,ii), based on an inferred continuing decline in numbers of mature individuals, and population fragmentation that has resulted in no population estimated to contain more than 250 individuals and for which at least 95% of mature individuals are contained within a single population (Big Salmon River).
Criterion D: Meets Endangered, D1 (less than 250 mature individuals). The 2003 fall spawning estimate was less than 100 adults, and the most likely estimate was 50-75.
Criterion E: Not applicable.