Atlantic salmon (Salmo salar) COSEWIC assessment and status report: chapter 10

Biology

The Atlantic Salmon is a member of the family Salmonidae. The fish of this family are fusiform in body shape with a distinguishing characteristic being the presence of an adipose fin between the dorsal and caudal fins that lacks rays. Fish of this family include the salmon, trout, and whitefishes and are commonly sought after by sport fishers in temperate zones. Species of this family generally prefer cool oligotrophic water and frequently exhibit migratory behaviour. Salmonids typically reproduce by digging nests or ‘redds’ in gravel substrates and depositing fertilized eggs. Atlantic Salmon carry out some of the most extensive migrations in the family, and have one of the widest distributions. It is the adaptation to this ocean-scale migratory behaviour that defines the life history and biology of the species.

Life Cycle and Reproductionxi

Atlantic Salmon display considerable phenotypic plasticity and variability in life history characters (Figure 12). They possess an innate ability to return to their 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’ (those that have spawned at least once previously). Most maiden salmon consist of smaller fish that return to spawn after one winter at sea and larger fish that return after two or more winters at sea (‘2, 3, or 4-sea-winter’, also designated as ‘multi-sea-winter’ [MSW]). There can be significant numbers of consecutive and alternate spawners present in any breeding season. Some rivers also possess a component that returns to spawn after only a few months at sea (0-sea-winter [0SW]). This life history strategy likely does not represent more than a minor component of most populations, with the exception of an unusual population in DU 3 that is entirely 0SW.

Figure 12: Generalized Life Cycle of the Atlantic Salmon

Diagram showing the generalized life cycle of the Atlantic Salmon.

(from O’Connell et al. 2006).

Collectively over its 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 redds (gravel nests), by oviparous mothers, usually occurs in October and November in gravel-bottomed riffle areas of streams or groundwater gravel shoals in lakes. Fertilization of eggs can involve both adult males and sexually mature precocious males (as young as age 1). 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 (Jones and Hutchings 2002). 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 or redds over the winter months and hatching usually begins in April. The hatchlings or 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, now referred to as ‘fry’ begin active feeding. Parr rear in fluvial and lacustrine habitats for 2-8 years after which time they undergo behavioural and physiological transformations and migrate to sea as smolt.

The substantial variation in freshwater smolt age and sea age at maturity creates substantial variation in age at spawning, ranging from 2-14 years. Typically, salmon smoltify between the ages of 2 to 5 years and return after 1-2 years at sea. A generation time of approximately 5 years is thought an appropriate estimate for much of the species’ range in Canada (O’Connell et al. 2006). Atlantic Salmon are a relatively short-lived fish species with a maximum age in the 12-14 year range with life spans typically falling in the 4-8 year range (Gibson 1993).

The phenotypic plasticity in life histories found within salmon populations tends to create relatively complex demographic population structures. Not only can the breeding individuals of a population consist of 7-8 cohorts, but sex ratios tend to be highly skewed across the range of age classes. For example, early maturing juveniles are almost exclusively male, while MSW fish are predominantly female in many populations. The exact proportions of mature male parr, grilse, 1, 2, and 3SW fish in a given population is highly variable and the mechanisms driving this differentiation remain unclear.

Fecundity varies considerably both within and among salmon stocks. Egg number and size increase with body size (Thorpe et al. 1984, Jonsson et al. 1996, O’Connell et al. 2008). In a dwarf or stunted freshwater resident population from Newfoundland, mean fecundity was 33.0 eggs (Gibson et al. 1996). In contrast, Randall (1989) reported mean fecundities of 12,606 and 16,585 eggs for 3SW and previous spawning salmon in the Restigouche River. Although absolute fecundity varies greatly among individuals, owing to high variability in adult body size, relative fecundity (eggs per kilogram) as a measure of reproductive effort varies much less and is inversely related to fish size. In the Miramichi River, New Brunswick, relative fecundity ranged from 1,331 eggs/kg in previous spawning salmon (mean length 82.1cm) to 2,035 eggs/kg in 1SW fish (Randall 1989). Rouleau and Tremblay (1990) reported values of 1,628 eggs/kg for 2SW salmon; 1,256 eggs/ kg for 3SW salmon; and 1,244 eggs/kg for repeat spawners. In a survey of 10 Newfoundland rivers, mean relative fecundity varied from 1,278 to 2,500 eggs/kg (O’Connell et al. 1997).

Natural mortality is highly variable both across and within life-stages of the Atlantic Salmon. Early survival from egg to smolt appears to be in the range of 0.03-3.0% (Chaput et al. 1998, Adams 2007, Fournier and Cauchon 2009, Gibson et al. 2009). Anadromous adult survival has been estimated in the range of 0.3-10% in recent generations (Reddin 2006, Fournier and Cauchon 2009), but reconstructions of historical runs suggest that marine survival may have been substantially higher in the past. For example, smolt-to-adult survival may have been about 15% in some Newfoundland populations when excluding marine fishery-related mortality (Dempson et al. 1998). This decline in marine survival has been implicated as a potentially important factor in the declines of salmon abundance.

Predationxii

Chaput and Cairns (2001) suggest that predation by birds and fish on drifting Atlantic Salmon eggs is a common phenomenon. The presence of salmon eggs has been reported in the stomachs of Atlantic Salmon and several other fish species (e.g., Brook Trout (Salvelinus fontinalis) and American Eel (Anguilla rostrata); Gibson 1973, Hilton et al. 2009).

A wide variety of predators feed on juvenile Atlantic Salmon, but predation by birds, particularly the Common Merganser (Mergus merganser), the Belted Kingfisher (Megaceryle alcyon), and the Double-crested Cormorant (Phalacrocorax auritus), is most widely documented (Cairns 1998, Dionne and Dodson 2002, Cairns 2006, DFO and MRNF 2008). Bioenergetic models estimate that Common Mergansers and Belted Kingfishers harvest 21-45% of juvenile salmon in Maritime rivers in each juvenile year (age 0+ to 2+) (Cairns 2001). In the northern portions of the species’ range, the Common Loon (Gavia immer) may also be a significant predator of juvenile salmon, consuming substantial amounts of biomass in lacustrine systems (Kerekes et al. 1994). Mammals such as Mink (Neovison vison) and Otter (Lutra canadensis) prey on juvenile salmon (DFO and MRNF 2008), as do adult salmon (mainly non-anadromous individuals) and other fish species.

Outgoing smolts may be eaten by returning adult salmon (in marine habitat), other fish species (e.g. Striped BassMorone saxatilis), mergansers, loons, gulls (Larus spp.), and seals (Phoca spp.) (DFO and MRNF 2008). Feltham (1995) estimated that Common Merganser predation removed 3-16% of smolt production in a Scottish river. Dieperink et al. (2002) tracked downstream movement of smolts in a Danish river with radio tags and determined that predation was light in the river, but was intense in the first few hours after sea entry, with major losses to gulls and cormorants. Larsson (1985) estimated that predation removed at least 50% of smolts from Swedish study sites before they reached the Baltic Sea. Higher survival (71-88%) was reported in smolts leaving Passamaquoddy Bay to the open Bay of Fundy (Lacroix et al. 2005). Fish known to feed heavily on salmon in estuaries, such as gadoids (Hansen et al. 2003), presumably also eat salmon in the open sea. Atlantic Salmon have been found in stomachs of Skate (Rajidae), Halibut (Hippoglossus hippoglossus), Porbeagle Shark (Lamna nasus), Greenland Shark (Somniosus microcephalus), and Pollock (Pollachius pollachius) (Wheeler and Gardner 1974, Mills 1989, Hislop and Shelton 1993, Hansen et al. 2003).

Salmon at sea may be preyed upon by Bottlenose Dolphins (Tursiops spp.), Belugas (Delphinapterus leucas) and Harbour Porpoises (Phocoena phocoena) (Middlemas et al. 2003). Seals and otters may prey on salmon in both freshwater and marine environments. In Europe, Thompson and MacKay (1999) found that 19.5% of returning salmon in northeast Scotland were scarred, but they felt, on the basis of scar patterns, that most of the damage had been inflicted by toothed whales and/or dolphins rather than by seals. Baum (1997) reported that 2% of adults returning to the Penobscot River in Maine had seal bites, and that the percent of scarred animals had risen in recent years. Avian predators, e.g. raptor species such as osprey (Pandion haliaetus) and bald eagle (Haliaeetus leucocephalus), also prey on adult salmon during migrations through estuaries and rivers (White 1939).

The Harp Seal (Pagophilus groenlandicus) population has increased concurrent with the salmon decline (Cairns 2001). Northern Gannets (Morus bassanus) from one colony (Funk Island) during one month (August) were estimated to consume 2.7% of post-smolt biomass in the NW Atlantic between 1990 and 2000 (Montevecchi and Myers 1997, Montevecchi et al. 2002). Gannet populations in the NW Atlantic approximately doubled between 1984 and 1999.

Physiologyxiii

Atlantic Salmon, are ectothermic and so are dependent upon the surrounding water temperature to cue migratory patterns, to drive metabolic processes, and to determine the rate of progression from one life stage to the next (Dymond 1963, Elson 1975, Wilzbach et al. 1998). Water temperature (along with river discharge) is an important factor affecting returning adults during river ascent (Banks 1969). Dependent upon the location of the population, adult salmon ascend spawning streams following afternoon temperature maxima between 16°C and 26°C (Elson 1975). Optimum temperature for egg fertilization and incubation is approximately 6°C (MacCrimmon and Gots 1979). Most juvenile growth occurs at temperatures above 7°C (Elson 1975). The preferred or optimal summer stream temperature for the growth and survivorship of Atlantic Salmon is 17°C (Javoid and Anderson 1967), while the upper incipient lethal temperature for Atlantic Salmon is 27.8°C (Garside 1973); however, adult and juvenile salmon may live for short periods above the incipient lethal temperature (Fry 1947). A sudden increase in incipient temperature in excess of 10°C may bring about the death of resident salmon at temperatures considerably below the upper lethal temperature (MacCrimmon and Gots 1979).

Atlantic Salmon juveniles undergo a series of changes at approximately 2-7 years of age (generally older in the northern part of the range) and at a critical body length (varies according to location and population), which lead to outmigration (McCormick et al. 1998). Behavioural changes include loss of positive rheotactic behaviour and territoriality, adoption of downstream orientation and schooling tendencies (McCormick et al. 1998). The out-migrating period is a critical stage for imprinting to chemical signals used for homing (McCormick et al. 1998). The transition is cued by photoperiod and temperature, while temperature and water flow appear to be key factors regulating the timing of downstream movements (McCormick et al. 1998). In the ocean, salmon are found at sea in water with SSTs between 1 and 12.5°C, with peak abundance at SSTs of 6-8°C (see Marine Habitat Requirements).

Acidification is an important freshwater stressor for Atlantic Salmon in some regions (summarized in DFO 2000). Increased H+ ion concentrations coupled with the low concentrations of Ca++ are responsible for increased mortality of salmon in acidified rivers of Nova Scotia. In fresh water, the osmotic gradient results in the passive diffusion of water into the blood and of ions out of the blood. Passive losses of ions are countered by active uptake of Na+ and Cl- from the water to maintain a balanced state. When pH is ≤ 5.0, active uptake of Na+ and Cl- is reduced and passive efflux is increased resulting in a net loss of both ions. The loss of ions results in a shift of water from the extracellular fluids (e.g., plasma) to the intracellular fluids, causing a reduction in blood volume. In addition, red blood cells swell and additional cells are released from the spleen. The reduced blood volume and increased number and size of the red blood cells may cause a doubling of blood viscosity and arterial pressure. Death is a result of failure of the circulatory system. Mortality due to exposure to low pH in fresh water varies with the life stage of salmon.

All freshwater stages are unaffected when pH is above 5.4 but mortality of fry (19-71%) and smolts (1-5%) occurs when pH is below about 5.0. Mortality of parr and smolts is relatively high (72-100%) when pH declines to the 4.6-4.7 range. Eggs and alevins begin to experience lethal effects at pH’s below 4.8. Levels of pH ≤5.0 also interfere with the smoltification process and seawater adaptation. Due to the natural buffering capacity of the ocean, acidification issues for Atlantic Salmon are restricted to freshwater environments.

Dispersal and Migration

Given that salmon have re-colonized glaciated portions of North America since glacial retreat, it is clear that this species has some ability to disperse to new habitat. Ocean-scale migrations also suggest the potential for extremely long-range dispersal (Reddin 2006). The natal fidelity that salmon exhibit has a limiting effect on the proportion of migrants among populations. Most data suggest immigration rates for Atlantic salmon are on average 10% per river or less (e.g. Dionne et al. 2008, Jonsson et al. 2003) and below the threshold required for demographic coupling. Most straying also appears to happen relatively close to the natal rivers (Jonsson et al. 2003), but recent evidence suggest mixing between rivers of different regions (Dionne et al. 2008). The presence of conspecifics in the destination river and the level of local adaptation may influence the success of strays. For example, return rates of stocked salmon decline as the distance between the stocked river and the source river increases (Ritter 1975). Furthermore, both natural immigrants and stocked salmon appear to have higher reproductive success when locally adapted populations are absent or suppressed (Mullins et al. 2003). In such cases, dispersal to new habitat and expansion of populations within freshwater systems can occur relatively rapidly (Mullins et al. 2003), particularly with human intervention (Bourgeois et al. 2000).

The migratory behaviour of both anadromous and potamodromous salmon is diverse. Some individuals move less than a few hundred metres their entire lives (Gibson 1993), some populations complete short migrations to estuaries or along the nearby coast, and many populations complete ocean-scale migrations (Reddin 2006). The migratory routes taken by individual populations may have some genetic basis (Reddin 2006), but even within populations there may be variability in migratory timing and route (Klemetson et al. 2003). This heritable migratory behaviour is likely due, at least in part, to local adaptation, meaning immigrants may be at a disadvantage compared to locally adapted residents, as suggested by Dionne et al. (2008) for Atlantic Salmon and Tallman and Healey (1994) and Hendry et al. (2000) for other salmonids.

Interspecific Interactionsxiv

Atlantic Salmon juveniles are territorial and year-class abundance declines over time as a result of competition for resources (Chaput 2001). Atlantic Salmon in fresh water compete for resources with conspecifics and potentially with other species, particularly other salmonids. Juvenile Atlantic Salmon are opportunistic predators of aquatic invertebrates (Gibson 1993), especially those drifting at the surface. Body size is the prime determinant of Atlantic Salmon territory size and, though environmental factors such as food availability may influence territory size, the degree of influence is first ‘filtered’ through an individual’s requirement for space (Grant et al. 1998). As such, competitors that exclude Atlantic Salmon from rearing habitat or use other resources of their freshwater environment will negatively affect Atlantic Salmon.

In some parts of the Atlantic Salmon’s range (particularly Newfoundland, Labrador and Quebec; Scott and Crossman 1973), non-anadromous forms of Atlantic Salmon occur in sympatry with anadromous runs. In some cases these life history variants are genetically distinct from anadromous individuals while in others there is no genetic divergence (Adams 2007). Non-anadromous juveniles are phenotypically indistinguishable from their anadromous counterparts and likely occupy similar niches at the expense of anadromous conspecifics.

Where Atlantic Salmon are sympatric with native Brook Trout, salmon displace trout from riffle habitat but may be at a competitive disadvantage in pools (Gibson 1993). Gibson and Dickson (1984) found that Atlantic Salmon juveniles showed enhanced growth in an otherwise fishless area of boreal Quebec, and also in a stream from which Brook Trout had been removed. However, density and biomass relationships between Brook Trout and Atlantic Salmon were not detected across several watersheds in another area of Newfoundland (Cote 2007). Similarly, no significant relationships between survivorship of Atlantic Salmon fry and abundance of Brook and Rainbow Trout were detected in streams of Vermont. Instead, fry survival was, in part, positively related to abundance of Brook Trout parr (Raffenberg and Parrish 2003).

Interactions between Atlantic Salmon and salmonids not native to eastern North America have also been studied. Rainbow Trout (Oncorhynchus mykiss), native to the Pacific coast, now occur in many Atlantic Salmon rivers and are expanding their range in some areas (e.g. Newfoundland; Porter 2000). While the two species demonstrate some degree of habitat overlap, and engage in some interspecific competition (Fausch 1998), juvenile Atlantic Salmon are more closely associated with positions near the substrate (riffle areas) and Rainbow Trout with the water column (or pool habitats) (Hearn and Kynard 1986, Volpe et al. 2001). Recent research conducted in Lake Ontario streams also suggests that Atlantic Salmon and Rainbow Trout juveniles can coexist successfully in streams where the habitat is suitable for both species (Stanfield and Jones 2003). Outcomes for salmon resulting from these interactions are often situation-specific, as habitat conditions (Jones and Stanfield 1993), dominance behaviour (Blanchet et al. 2007) and prior residence come into play (Volpe et al. 2001). Blanchet et al. (2008) suggested that increased daytime activity in the presence of juvenile Rainbow Trout might increase predation risk for juvenile Atlantic Salmon.

Two other Pacific-origin salmonids, Chinook Salmon (Oncorhynchus tshawytscha) and Coho Salmon (Oncorhynchus kisutch), occur in the Great Lakes. High densities of stocked Chinook Salmon have potential to negatively affect Atlantic Salmon behaviour and survival (Scott et al. 2003) and interfere with spawning behavior (Scott et al. 2005). Similarly, Coho Salmon can affect growth and survival (Jones and Stanfield 1993); however, they are much less likely to have significant impacts due to relatively low abundance and different habitat requirements (Stanfield and Jones 2003).

Atlantic Salmon and Brown Trout (Salmo trutta) interactions are relatively well studied. The Brown Trout, a native of Europe, has been introduced to numerous North American systems used by Atlantic Salmon and appears to be expanding its range in Newfoundland (Westley et al. submitted). Brown Trout tend to use the margins of runs and pools where water velocity is lower, in contrast to riffle specialization by Atlantic Salmon (Fausch 1998, Bremset and Heggenes 2001, Heggenes et al. 2002). Gibson and Cunjak (1986) reported that introduced Brown Trout in the Avalon Peninsula, Newfoundland, were largely segregated from Atlantic Salmon by habitat choice and to some degree, by food habits. Nevertheless there is overlap in types of habitat used by the two species (Heggenes and Dokk 2001). The occurrence of competition between Brown Trout and Atlantic Salmon is not universal (e.g. Gibson and Cunjak 1986) and appears to be scale-dependent (sample resolution of studies reporting competition are generally <100 m2; Westley et al. submitted). Negative impacts include competition for females, winter shelter (Harwood et al. 2002a,b) and spawning habitat, and genetic and survival repercussions associated with hybridization between Brown Trout and Atlantic Salmon (Gephard et al. 2000). Competition between these species is most intense at spawning and early juvenile stages (Westley et al. submitted). In general, seemingly contradictory results suggest that the view that competition forces an inverse relation between other salmonids and Atlantic Salmon populations may not be tenable at all geographic scales (Cairns 2006).

There are several other non-indigenous species of freshwater fish that have become established in many watersheds containing wild Atlantic Salmon. The species of most concern include Smallmouth Bass (Micropterus dolomieu), and species in the pike family: Chain Pickerel (Esox niger) and Muskellunge (Esox masquinongy). These species are potentially both competitors and predators of juvenile Atlantic Salmon. Introductions are generally the result of directed and illegal transfers of live fish between watersheds. The introduction of non-native species into existing salmon habitat represents a real and expanding threat to the persistence of salmon in the affected and adjacent drainages (DFO and MRNF 2009).

Correlations between survival and growth during first summer/winter at sea suggest food resources may be a limiting factor during some marine phases (Peyronnet et al. 2007). However, variable environmental conditions in the ocean, rather than competition-induced shortages, are provided as explanations driving marine growth (Peyronnet et al. 2007). Examinations of smolt output and sea survival suggest these two parameters are not linked (Gibson 2006, Reddin 2006) and provide indirect evidence that competition in marine waters is relatively unimportant for Atlantic Salmon. Unfortunately, the vast scale of the Atlantic Salmon’s ocean habitat precludes field experiments to directly measure competitive interactions of Atlantic Salmon with other species (Cairns 2006).

Interactions with prey species in the marine environment may also play an important role in marine survival. Studies from the eastern Atlantic show Atlantic Salmon prey on a variety of taxa including, but not limited to: Atlantic Herring (Clupea harengus), Capelin (Mallotus villosus), Sandeels (Ammodytidae), Gadids, Lantern Fishes (Myctophidae), Barracudinas (paralepidids), various invertebrates (amphipods, copepods, euphausids and crustaceans (shrimps)) (Haugland et al. 2006). Atlantic Salmon appear to focus on invertebrates early in their marine phase, but fishes appear to become a more important diet item as salmon grow older and larger (Reddin 1988, Hislop and Shelton 1993, Hansen and Quinn 1998). The diet of Atlantic Salmon in the marine environment is variable both temporally and spatially, suggesting they feed opportunistically as they migrate. This variability in diet makes it difficult to link marine growth and survival to the abundance of specific prey species.

Numerous disease-causing agents have been identified in wild Atlantic Salmon (Bakke and Harris 1998). These include Renibacterium salmoninarium (bacterial kidney disease (BKD) causing agent), Aeromonas salmonicida (furunculosis), infectious pancreatic necrosis virus, Vibrio anguillarum and Edwardsiella tarda (DFO 1999). There is documented history of some of these diseases in Maritime rivers including furunculosis and BKD (Cairns 2001). Furunculosis can become an important factor in adult in-river survival especially during periods of low flow and warm water. A new disease agent, infectious salmon anemia virus (ISA), was discovered in aquaculture-reared fish in 1997 (DFO 1999). Myxozoa species (likely introduced) have also been reported in juvenile Atlantic Salmon from several Canadian rivers (Dionne et al. 2009b).

Within Lake Ontario, recent emergence of viruses new to the Lake Ontario basin have the potential to cause disease and mortality in wild Atlantic salmon (e.g. Viral Haemorrhagic Septicaemia (VHS) detected in 2005). Additionally, salmonid species in Lake Ontario are carriers of the bacteria known to cause bacterial kidney disease (BKD). Atlantic Salmon strains currently being reared to support Lake Ontario restoration efforts are susceptible to disease outbreaks and seasonal mortality when infected with these bacteria.

Adaptability

Atlantic Salmon exhibit a wide range of variation in both phenotypic plasticity and adaptive genetic variation across its range (Taylor 1991, Gibson 1993, de Leaniz et al. 2007). From individuals that spend their entire life cycle within a few metres of the natal stream and attain a size of < 10 cm, to 100+ cm individuals that undertake ocean-scale migrations, it is clear that this species has the capacity to adapt to a wide variety of conditions on relatively short demographic and evolutionary scales (Gibson 1993). However, while Atlantic Salmon appear to be flexible within the natural range of variation for freshwater habitat in eastern Canada, the species does not appear to adapt well to major anthropogenic disturbances. In particular human activities that interrupt migratory behaviour (e.g., dams), or drastically impact water quality (e.g., acidification) have led to extirpations in the past (Amiro 2003).

This species adapts well to domestication as is evident in the global aquaculture industry. Recent studies suggest that salmon show a selection response to domestic conditions within a single generation. Unfortunately, rapid selection under domestic conditions can create challenges when attempting to supplement natural populations with hatchery-raised fish. Genetic data suggest that stocked fish have often had limited reproductive success (e.g., Fontaine et al. 1997, Saltveit 2006). Transplants of wild stock have been relatively rare. However, there have been documented successes (e.g., Rocky River in DU 4) (Bourgeois et al. 2000), usually within a short geographic distance between source and destination sites and into habitats devoid of naturally occurring anadromous populations. Transplanting salmon among DUs may be more difficult due to a higher probability of maladaption. For example, Ritter (1975) showed declining return rates of stocked salmon as the distance to the source population increased. de Leaniz et al. (2007) recently reviewed much of the evidence for local adaptation and the role it plays in Atlantic Salmon fitness and ultimately population dynamics. The authors concluded that while local adaptation is likely important, quantitative evidence of its role in processes such as migratory timing, disease resistance or growth rate are scarce.




Footnotes

xi Elements of this section have been copied, abstracted and/or synthesized from DFO and MRNF (2008).
xii Elements of this section have been copied, abstracted and/or synthesized from Cairns (2006) and DFO and MRNF (2008).
xiii Elements of this section have been copied, abstracted and/or synthesized from DFO (2000) and COSEWIC (2006a).
xiv Elements of this section have been copied, abstracted and/or synthesized from DFO and MRNF (2008), DFO and MRNF (2009), Wesley et al. (submitted) and COSEWIC (2006a, 2006b).

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