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

Biology

 

General

The biology of the Atlantic salmon is relatively well known (e.g., Baum 1997, Scott and Crossman 1998).  Appendix 1 provides a general summary; the sections below describe biological characteristics common to iBoF Atlantic salmon. 

 

Biology of the Inner Bay of Fundy Atlantic Salmon DU 

The best life history and demographic data on iBoF Atlantic salmon come from two major salmon-producing rivers, the Big Salmon and the Stewiacke (Table 1), and are described by Amiro (2003).

Most iBoF parr smoltify after two years in freshwater at a size probably similar to that outside the DU, but perhaps as late as July in some rivers (e.g., Little River, tributary to the Stewiacke River).  Migration patterns of iBoF salmon after entering the marine environment are unclear (see SPECIES INFORMATION).  Whereas other salmon populations (e.g., Maine) migrate to distant waters off Labrador and Greenland (Baum 1997), iBoF salmon may remain resident to the Bay of Fundy and Gulf of Maine.  Alternatively, migration might be merely delayed by distance and local oceanic conditions.  Regardless of migration patterns, almost all iBoF salmon mature after one winter at sea and spawn in consecutive years, unlike the later age of maturity and alternate-year repeat spawning of neighbouring Maine.  The best estimates of historical marine survival come from a study of wild Big Salmon River smolt returns for 1966 through 1971 (Ritter 1989), and range from 1.0% to 9.7% (mean = 6.0%); current return rates for the Big Salmon River (2002 smolts) are approximately 0.3% (Gibson et al. 2004).  The best estimate of generation time for iBoF salmon is 3.7 years, calculated from the average age to smolt migration of 2.6 and the average age to first maturity of 1.1 years, as reported for the Big Salmon River (1965 to 1973, by Jessop cited in Amiro 2003).  An unpublished study in one tributary suggests that a relatively high proportion of male parr may mature in fresh water and may survive to smoltify (Amiro 2003).  Mature male parr are capable of fertilizing substantive portions of egg batches under controlled experimental conditions and probably contribute positively to effective population size (e.g., Jones and Hutchings 2002).  However, these mature male parr have not been entered into the calculation of generation time because their proportional contribution to spawning in any of the iBoF salmon rivers has not been estimated.  The best estimate of body size, for females, is 61.5 cm, and average egg production is 4,060 eggs, based on data from the Big Salmon River (1965 to 1973) (Amiro 2003).  This estimate may, however, include hatchery fish. An unpublished study apparently suggests that the fecundity/body-size relationship of iBoF salmon is similar to that of oBoF and Scotian Coast/Uplands populations (Amiro 2003).  Although the majority of iBoF salmon mature after one sea-winter, the relatively high across-year survival of females is thought to result in repeat spawners contributing the majority of eggs and thus recruits.  Amiro (2003) has calculated, based on a total sample of 3,334 adults returning to the Big Salmon river from 1965 through 1973, that repeat-spawning individuals contributed 68% of the potential egg deposition.  Although one-sea-winter adults comprise 50% of the population, they only contribute 25% of the potential egg deposition (the remaining 7% comes from the maiden two sea-winter females).

 

Big Salmon River

Table 1.  Distribution by age-at-first maturity, one sea winter (1SW) and two sea winter (2SW), post-smolt age, spawning history, mean length, fecundity, percent female, and percent-at-age of salmon in the Stewiacke and Big Salmon Rivers.  Stewiacke River values were determined from 298 aged scale samples collected from the commercial and the angling fisheries, 1983.  Big Salmon River values were determined from 3,334 aged scale samples collected from salmon at a counting fence operated 1965-1973.  From Amiro (2003).
Post-
smolt age
Spaw-
ning
history

1st
Spaw-
ning
history

2nd
Spaw-
ning
history

3rd
Spaw-
ning
history

4th
Spaw-
ning
history

5th
Spaw-
ning
history

6th
NumberMean
length
fe-
males

(cm)
Mean
fecun-
dity

(eggs)
Per-
cent
female
Per-
cent
of

sample
1SW           
10     1,65952.93,1426649.8
21     67363.14,2636720.2
312    48371.95,5468114.5
4123   18978.16,676925.7
51234  4583.17,7521001.3
612345 783.57,8461000.2
7123456188.08,9751000.0
2SW           
20     13271.65,497894.0
32     11577.56,557863.4
423    2581.67,412920.7
5234   581.67,412800.1

 

Stewiacke River

Table 1.  Distribution by age-at-first maturity, one sea winter (1SW) and two sea winter (2SW), post-smolt age, spawning history, mean length, fecundity, percent female, and percent-at-age of salmon in the Stewiacke and Big Salmon Rivers.  Stewiacke River values were determined from 298 aged scale samples collected from the commercial and the angling fisheries, 1983.  Big Salmon River values were determined from 3,334 aged scale samples collected from salmon at a counting fence operated 1965-1973.  From Amiro (2003).
Post-
smolt age
Spawning
history

1st
Spawning
history

2nd
Spawning
history

3rd
Spawning
history

4th
Fresh
water
age
NumberMean
length
(cm)
Mean
fecundity

(eggs)
Percent
female
Percent
of
sample
1SW          
10   220452.72,9997368.5
10   31254.93,252504.0
21   23864.44,6136612.8
21   3861.84,192622.7
312  2973.06,331893.0
312  3271.66,0131000.7
31   2778.07,6101002.3
512342196.314,9231000.3
2SW          
20   2772.16,1251002.3
20   3275.06,8141000.7
32   2379.48,012661.0
32   310.3
423  2480.88,4361001.3

Many species may prey upon the iBoF Atlantic salmon, including birds (e.g., kingfishers, mergansers, cormorants and gannets), fish (e.g., striped bass), and seals.    While it is unlikely that predation in fresh water has contributed to the decline of the iBoF salmon, predation during the smolt migration and in the marine environment may play a role.  In some areas, gulls, gannets and cormorants are believed to have taken large numbers of smolts and post-smolts.  For example, Montevecchi et al. (2002) report that gannet predation of Atlantic salmon off Newfoundland increased by more than ten-fold between the 1980s and the 1990s. Smolt and post-smolt iBoF Atlantic salmon may also be subjected to predation by marine mammals in the Bay of Fundy, such as harbour seals (Phoca vitulina) and grey seals (Halichoerus grypus), although the level of this predation mortality has not been estimated.  An acoustic tracking study of post-smolts (Lacroix et al. 2005) suggests that the mortality of iBoF salmon during the first months after leaving the river (when post-smolts are believed to be particularly vulnerable to predation) is surprisingly low.

Finally, a large number of diseases and parasites are known to infect Atlantic salmon.  Their pathology is of interest, in part, because of the aquaculture industry.  The incidence of fish diseases and disease agents, found at freshwater and marine sites, for farmed (1993-1998) and wild (1987-1998) salmonids in the Canadian Maritime provinces, have been documented by Mackinnon et al. (1998).  Of 11 diseases and disease agents examined in the Maritimes (excluding sea lice), 10 were reported from aquaculture sites and 5 were reported from wild populations.  In New Brunswick, of the 6 diseases and disease agents reported in fish farms (excluding sea lice), 3 have been reported in wild populations.  There is at least one documented example of the appearance of a disease in wild Atlantic salmon that had previously only been documented in farmed Atlantic salmon.  Until 1998, the infectious salmon anemia virus (ISAv) had only been found in farmed Atlantic salmon reared in net pens.  In 1998, for example, samples from 911 wild fish from New Brunswick and Nova Scotia (including 335 non-salmonids and 576 salmonids) were tested for the presence of ISAv, using the head kidney (SHK) cell line; the tests were negative for each sample (Mackinnon et al. 1998).  However, in 1999, wild Atlantic salmon from the Magaguadavic River, New Brunswick, tested positive for the ISA virus (www.asf.ca).  Although it is not known how the wild salmon contracted the virus, it is the first documented case of ISAv in wild Atlantic salmon.  In early 2001, the ISAv was found for the first time in Maine farmed Atlantic salmon (Young 2001).