Atlantic salmon (Salmo salar) COSEWIC assessment and status report: chapter 12

Threats and Limiting Factorsxx

The causes of the widespread decline of Atlantic Salmon (WWF 2001) are not well understood. Several major reviews have attempted to identify and prioritize causes but  there is currently no consensus. For example, a group of experts discussed 62 factors potentially threatening the survival of Atlantic Salmon in eastern North America (Cairns 2001). Of the 12 leading factors, five were related to predation, five to life history, one to fisheries, and one to physical/biological environment. Furthermore, two were related to freshwater life stages, nine were related to marine life stages, and one was related to a freshwater cause that manifested itself in the marine stage.

Throughout the range of Atlantic Salmon, poor marine survival has been cited as the primary cause for observed declines (Potter and Crozier 2000, Reddin et al. 2000, Amiro 2003, Gibson et al. 2004, 2009). Poor marine survival continues to threaten many populations of Atlantic Salmon despite a massive reduction in fishing mortality (COSEWIC 2006b) and adequate freshwater conditions in most, but not all (see DU 14) areas (DFO 2008, Breau et al. 2009, Cameron et al. 2009, Chaput et al. 2010). While the mechanism(s) of marine mortality is uncertain, what is clear is that the recent period of poor sea survival is occurring in parallel with many widespread changes in the North Atlantic ecosystem.

Changes in climate in the early 1990s have resulted in significant physical and biological changes in the North Atlantic including: an enhanced outflow of low-salinity waters from the Arctic through the Labrador Sea, enhancement of stratification on the northwest Atlantic shelf, changes to the seasonality of phytoplankton production, greater abundance of small copepods and a decrease in abundance of older life stages (Greene et al. 2008). The relationship between salmon abundance and temperature is reasonably well established (Friedland et al. 1993) and therefore changes related to sea surface temperature may be some of the key factors affecting natural mortality (Cairns 2001).

The impacts of climate will not be limited to marine environments. From 1990–2100, mean surface air temperature is projected to increase by 1.4-5.8ºC, with more rapid warming in the Northern regions of North America (IPCC 2001). In Atlantic Canada, a 2-6°C increase is expected in the next century with increases in air temperature expected to be greatest in western New Brunswick and Quebec, and lowest in Labrador. The responses of Atlantic Salmon populations across its range in eastern Canada are uncertain, but they are expected to differ across the latitudinal range.

Directed fishing has had catastrophic effects on many fish species (e.g. Pauly et al. 2002) including Atlantic Salmon. In Lake Ontario, directed fishing acted in concert with habitat loss to collapse the Atlantic Salmon fishery within 26 years of beginning commercial-scale harvesting (Dunfield 1985). This population was subsequently extirpated by the turn of the 20th century (COSEWIC 2006a).

In eastern Canada, the final closure of major intercept fisheries in 1992 shifted the emphasis of commercial mixed stock salmon fisheries towards Aboriginal and recreational salmon fisheries on river-specific stocks. Fisheries are principally managed on a river-by-river basis and, in the few areas where retention of the dominant egg-bearing size group is allowed, harvests are closely controlled to achieve conservation goals (based on egg-deposition rates). Harvests by all users in Canada in 2008 totalled 132t, the lowest of 47 years of record and only about 5% of peak landings reported 1960 – 1980 (DFO and MRNF 2009). These landings constituted approximately 9.5% of returns to Canadian rivers in 2008.

In 2006, 64% of the reported harvest of Atlantic Salmon occurred in the recreational fisheries. In this fishery, 100% of the effort occurs in fresh water and is therefore river-specific. Impacts of recreational fishing are managed with retention quotas, restrictions on retaining large salmon, gear types, exclusive catch and release fisheries and complete closures. Harvest in the total Canadian recreational fisheries in 2006 was 35,171 small and large salmon (7% of total returns), of which slightly less than 10% were large (MSW) salmon; this was the lowest total harvest reported in 33 years of record (ICES 2007).

The practice of catch and release has increased in recreational fisheries. In 2006, about 58% of the total number of salmon caught were released (ICES 2007). Under the right conditions, catch and release angling is considered to be a useful management tool (Dempson et al. 2002) but still results in some mortality. Water temperature and handling duration are among factors that affect the survival rate of released fish. The incidence of short-term mortalities in Newfoundland were observed to be ~10% (Dempson et al. 2002). Values of 3-10% are used when accounting for catch and release-related mortality in stock assessments in Atlantic Canada.

Limited Aboriginal food fisheries take place in eastern Canada, subject to agreements or through licences issued to Aboriginal groups. Most of these fisheries occur in fresh water or in estuaries close to river mouths. Although the reports of harvests are incomplete, the fisheries often affect river-specific stocks. In large areas of eastern Canada, Aboriginal harvests of Atlantic Salmon have been curtailed due to concern about stock status, at times on a voluntary basis. Some of the Aboriginal food fisheries of Labrador take place in what are considered to be coastal waters. These fisheries have moved closer to river mouths and likely harvest few salmon from other than local rivers. The estimated harvest in all Aboriginal peoples’ fisheries in 2006 was 59t, the second highest of 17 years of record (ICES 2007).

Commercial fisheries for Atlantic Salmon in Canadian waters, which as recently as 1980 yielded a harvest of 2,412t (ICES 2007), have been closed since 2000. Salmon of Canadian origin are still captured in the marine fisheries of St. Pierre and Miquelon and at West Greenland. Reported harvests of the St. Pierre and Miquelon marine gill net fishery have ranged between 1.5 and 3.6t per year over the past 10 years (ICES 2007). In the context of total harvests, the fishery is small but it is a mixed stock and interception fishery. A recent genetic analysis of a sample of the catches from 2004 indicated that 98% of the fish were of Canadian origin (ICES 2006). As this fishery occurs in a marine area adjacent to the south coast of Newfoundland, it likely has an impact on stocks of the immediate area and the Maritime Provinces.

The fishery of West Greenland is a mixed stock interception fishery and harvests fish of North American and European origin. The salmon caught in that fishery are mostly (>90%) non-maturing 1SW salmon, most of which are destined to return to home waters as multi-sea-winter (2SW primarily) fish. Fish from all multi-sea-winter producing areas of eastern Canada are intercepted in this fishery. In the past ten years, the harvested fish have been predominantly North American in origin. The fishery, which is conducted for local consumption, had a reported harvest of between 2,300 and 4,000 fish of North American origin from 2002 to 2006 (ICES 2007).

Illegal harvests of Atlantic Salmon occur in both marine and fresh waters to varying degrees throughout Atlantic Canada. Poaching in marine waters is more frequent in waters around Newfoundland and Labrador and the Quebec Lower North Shore than elsewhere (DFO and MRNF 2009). In Newfoundland, net-scarred salmon (those that had survived entanglement within nets) approached 10% in some rivers of Newfoundland (Dempson et al. 1998). Illegal harvesting is most frequently carried out using gillnets or bait nets, the latter illegally set so as to increase the bycatch of salmon (DFO 2007). Poaching in inland waters is carried out by a variety of means, including jigging and sweeping of pools by nets (DFO 2007). Some management measures deter illegal fishing through fostering community stewardship, targeted enforcement and protecting salmon in vulnerable freshwater habitats. While quantification of the magnitude of mortality associated with illegal fishing is difficult, circumstantial evidence suggests mortality related to illegal fishing can imperil localized stocks (e.g. Cote 2005).

Bycatch associated with monitored commercial fisheries is not considered significant. Bycatch through commercial fisheries is thought to have significantly declined due to the moratorium on some groundfish species since 1992. Dempson et al. (1998) indicate very few salmon are caught in both inshore and offshore fisheries. Bait-fishing is also thought to cause minimal bycatch given current bait-fishery restrictions (Reddin et al. 2002). Bycatch from Aboriginal fisheries off Labrador do result in salmon mortality. However, these catches count against established quotas, which when reached, trigger additional measures to limit mortality of salmon (ICES 2007). The bycatch of the Ungava Aboriginal fishery is, however, considered “significant” (DFO and MRNF 2009). There are no reported bycatches of salmon from any other Aboriginal fisheries in eastern Canada.

Obstructions can severely reduce the productive habitat and production of salmon (DFO and MRNF 2008). Low head and surmountable dams delay, at the very least, upstream migration until such time as water discharges are adequate for salmon to leap the obstruction. Higher dams equipped with fish passages have varying passage efficiencies, 100% being very uncommon (Fay et al. 2006). Even when upstream passage is available, the impoundments behind these dams can delay and/or prevent smolt emigration, increase the energetic costs of smolt movements and, dependent on discharge conditions, can result in increased predation (NRC 2004).

In addition to direct loss of productive habitat from flooding, dams also alter natural river hydrology and geomorphology, interrupt natural sediment and debris transport processes, and alter natural temperature regimes (Ruggles and Watt 1975, Wheaton et al. 2004). These impacts can adversely change aquatic community composition and affect the entire aquatic ecosystem structure and function.

Ruggles (1980) identified the following unnatural conditions created by dams that can threaten anadromous salmonid populations: passage over spillways, passage through turbines, passage through impoundments, exposure to atmospheric gas saturation, pollutants, predators, unnatural temperatures, disease organisms and increased vulnerability to exploitation from angling. Smolts are vulnerable to the impacts of dams and may become impinged on screens, entrained in forebays, accrue lethal abrasions or be killed in turbines during downstream migration. Dams can also alter flow patterns of rivers, increase water temperature, and concentrate pollutants, all of which are factors that can adversely affect resident parr and migrating smolts (Foerster 1934, Saunders 1960). Entrainment mortality for salmonids can range between 10-30% at hydroelectric dams (Fay et al. 2006). Passage through turbines can also lead to indirect mortality from increased predation and disease (Odea 1999). Where multiple dams exist, the losses of downstream migrating smolts from turbine entrainment are often cumulative and biologically significant (Gibson et al. 2009). Because of their larger size, turbine mortality of kelts is expected to be significantly greater than 10 to 30% (FERC 1997). Mortality of salmon in hydropower generation plants, although potentially mitigated with fish passage facilities and water management, can pose a significant threat to the persistence of Atlantic Salmon.

Juvenile Atlantic Salmon can use extensive areas of freshwater habitat (e.g. Robertson et al. 2003) and must be able to access feeding and refuge habitat. Lack of habitat connectivity affects the abundance and distribution of Atlantic Salmon populations but may also reduce access to habitats, which improve growth (e.g. Hutchings 1986) and survival (Breau et al. 2007).

Improperly designed culverts create barriers to fish passage through hanging outfalls, increased water velocities, or insufficient water velocity and depths within. After a study of culvert installation on the newly constructed Trans-Labrador Highway, Gibson et al. (2005) concluded that culverts create more passage barriers to fish passage than other structures. Culverts can also degrade habitat quality through direct loss of habitat through scour, deposition of sediment and loss of food production within the vicinity of the crossing (Bates 2003).

Water withdrawals for agricultural, mining, or other industries can directly impact Atlantic Salmon spawning and rearing habitat (Maine Atlantic Salmon Task Force 1997). They have the potential to expose and reduce salmon habitat and contribute to more variation and higher water temperatures. Adequate water quantity and quality are especially critical to adult migration and spawning, fry emergence and smolt emigration (DFO and MRNF 2008). During summer and winter low flows, juvenile salmon survival is directly related to discharge (Gibson 1993, Cunjak 1988, Cunjak 1996), with better survival in years with higher flows (Ghent and Hanna 1999). As a result, water withdrawals have the potential to limit carrying capacity and reduce parr survival.

Land management activities, particularly land clearing for development, has the potential to negatively affect freshwater habitat of salmon and food sources. Habitat alteration resulting from sedimentation, run-off pollution, channelization and changes to hydrological regimes are all associated with development (Trombulak and Frissell 2000, Wheeler et al. 2005, Fay et al. 2006).

Juvenile salmon can be adversely affected by contaminants in fresh water. Pesticide effects on salmonids may range from acute (e.g. fish kills in PEI; Cairns et al. 2009) to chronic (leading to increased cumulative mortality; DFO and MRNF 2009). Sub-lethal concentrations of contaminants, such as endocrine-disrupting chemicals, may compromise survival of salmon at sea (Fairchild et al. 2002, Moore et al. 2003, Waring and Moore 2004). Sources of these compounds may include agriculture, sewage, pesticide spraying (e.g. forest spraying; Fairchild et al. 1999) and industrial effluents (e.g. pulp and paper mills; McMaster 2001). A caging study in the Miramichi River showed a general trend of better feeding and growth in Atlantic Salmon smolts caged at sites with fewer known anthropogenic inputs, of which pulp and paper mill effluent was a major contributor (Jardine et al. 2005). In addition, chemical pollution from chlorinated organic compounds, which are widely distributed in the North Atlantic Ocean, has been proposed as a complementary factor affecting the sea survival of Atlantic Salmon (Scott 2001). The limited studies to date have only examined a minute number of the vast variety of chemicals currently being used and introduced.

Acidification of fresh water in eastern Canada is primarily a result of depositions of airborne pollutants originating in the central U.S. and Canada, though inputs are augmented by local sources as well (DFO 2000). Currently, acid impacts on Atlantic Salmon are most pronounced in the Southern Upland region of Nova Scotia (DU 14) where 22% of rivers are acidified and have lost populations and a further 31% are moderately impacted by acidification and maintain remnant populations (DFO 2000). Assuming a smolt-to-adult return rate of 5%, a value higher than is presently being observed, acidification impacts will likely result in the extirpation of 85% of the Southern Upland populations. The underlying geology of the Southern Upland is the principle reason for the vulnerability to acidification.

Other areas in Atlantic Canada that are somewhat vulnerable to the effects of acid depositions are southwestern and northeastern Newfoundland (Environment Canada 2004). Although there has been a reduction in sulphate emissions and depositions, there has not been a corresponding increase in pH or acid neutralizing capacity in these areas. Furthermore, at the projected sulphate deposition rates, the time for recovery of base cations in these catchments is 60-80 years (Clair et al. 2004). Based on the cumulative effects and extirpations, the estimated time to recovery for affected drainages, and the large area affected, acidification remains a significant threat to one DU (14, Nova Scotia Southern Upland) and is a burden if not a threat to perhaps one other (DU 4) in Newfoundland.

Infiltration of sediment into stream bottoms has been suggested as a cause for significant decrease in the survival, emergence and over-wintering success of Atlantic Salmon juveniles (Chapman 1988). Sediment size and movement in a stream (bedload) is a natural process; however, a multitude of impacts can greatly increase the input and accumulation of sediments to streams (Meehan 1991, Wheeler et al. 2005). The result is the loss of habitat as interstitial spaces become filled with sediment. All but the oldest of juvenile salmon occupy interstitial spaces at some stage and therefore exceeding the equilibrium input of sediments into streams can have devastating effects. As little as 0.02% silt has been shown to decrease the survival of eggs to the pre-eyed stage by 10% (Julien and Bergeron 2006). As stated above, sedimentation is often a by-product of road construction, urban development, agriculture and some industries.

Aquaculture is an industry associated with much controversy as inferences have been made that associate the decline in European wild salmon stocks with the rise in farmed salmon production (e.g. Gausen and Moen 1991, Heggberget et al. 1993, Hansen et al. 1997). Similar concerns have been voiced in eastern Canada, as growth of the Canadian industry has coincided with severe declines in wild populations in nearby rivers in the Bay of Fundy (DU 15, 16) and the Bay D’Espoir region (DU4) of the south coast of Newfoundland (Carr et al. 1997, Amiro 1998, Chang 1998, Dempson et al. 1999).

The concern for wild stocks is based on the potential for interactions that result in inter-breeding and subsequent loss of fitness, competition for food and space, disruption of breeding behaviour, and transmission of disease (Cairns 2001). In North America, farm-origin salmon, have been reported in 87% of the rivers investigated within 300 km of aquaculture sites (Morris et al. 2008). Though the abundance of farmed salmon in rivers is highly variable, it can exceed those of wild fish (Jones et al. 2006, Morris et al. 2008). There is strong evidence for the introgression of genetic material from European-origin aquaculture salmon into some wild Atlantic Salmon populations within the inner Bay of Fundy (Patrick O’Reilly, pers. comm.).

Even small percentages of escaped farmed salmon have the potential to negatively affect resident populations, either through demographic or genetic changes in stock characteristics (Hutchings 1991). There have been many reviews and studies showing that the presence of farmed salmon results in reduced survival and fitness of wild Atlantic Salmon, through competition, interbreeding and disease (e.g., Gross 1998, Fleming et al. 2000, NRC 2002, 2004, McGinnity et al. 2003). For example, an experimental cross between 4th-generation farmed Atlantic Salmon of the Saint John River and wild individuals from the Stewiacke River, showed a significant decrease in F1 survival to the pre-eyed embryonic stage relative to pure crosses (Lawlor 2003). The use of more exotic species (e.g. rainbow trout) in and around salmon rivers could also pose a problem with escapes into the wild (see interspecific interactions).

Another concern related to aquaculture is the possibility of disease/parasite transmission from artificially propagated fish to wild stocks. In Norway many salmon populations have been destroyed by the parasite Gyrodactylus salaris (Heggberget et al. 1993, McVicar 1997) and over 70 rivers affected with furunculosis (Johnsen and Jensen 1994; in both cases the outbreaks originated with hatchery-propagated salmonids. However, in North America there is no evidence to indicate that farmed salmon have transferred these diseases to wild fish (DFO 1999).

It has been suggested that intensive aquaculture may cause salmon to alter migratory behaviour (Amiro 2001), and that attraction of predators such as seals to aquaculture facilities might result in an increased rate of predation of wild fish in the area (Cairns and Meerburg 2001), but both of these suggestions remain unverified.

As outlined in Interspecific Interactions, invasive and/or introduced species have potential to negatively interact with Atlantic Salmon, particularly in freshwater. Potential interactions include predation, competition for habitat, food and mates as well as hybridization. In the Great Lakes, Zebra Mussels (Dreissena polymorpha) and Alewife (Alosa pseudoharengus) may have created conditions that are less conducive to restoration efforts. The latter has also been implicated in the collapse of Lake Ontario Atlantic Salmon. Endemic salmon may have suffered the effects of thiamine deficiency (including mortality and impaired ability to reach spawning grounds) as alewife became a prominent food source (Ketola et al. 2000). In general, negative interactions between salmon and non-native species are often context-specific or not well understood.

In areas where populations have collapsed, further declines caused through inbreeding depression and abnormal behaviour associated with low population size are a concern (e.g. iBoF; COSEWIC 2006b).

Cairns (2001) noted that it is very improbable that the decline in Atlantic Salmon is due to any single cause, and factors contributing to a decline are likely to have acted in a cumulative manner (see projections of Gibson et al. 2009 for an example of cumulative interactions of stressors). Directed fishing and habitat alterations are considered in many DUs to have a medium effect on populations (DFO and MRNF 2009). A semi-quantitative assessment, by regional fisheries scientists and managers, of the impact of habitat-related threats to salmon is summarized by DU in Table 3 (taken from DFO and MNFR 2009). Potential sources of mortality were assessed with respect to the proportion of salmon that would be affected, and the time frame in which salmon had been vulnerable to the threat. The most wide-ranging habitat threats to Atlantic Salmon originate from transportation infrastructure, agriculture, forestry and mining operations, and municipal waste-water discharge. The least severely threat-impacted areas are in Quebec, Newfoundland and Labrador (DUs 1-9). Conversely, the Maritime Provinces (DUs 14-16) are the most severely threat-impacted with several threats affecting > 30% of salmon or a loss of > 30% of spawners (Table 3). Salmon of DU 14 (Nova Scotia Southern Upland) are severely impacted by acid rain, which has caused the loss of populations in several of the 63 rivers within the DU. In combination with the persisting low marine survival (ecosystem change) listed for DUs 12-16, acid rain is threatening the loss of the majority of the remaining salmon populations within that area (Amiro 2000, DFO 2000). Based on the ubiquitous effects poor marine survival is having on Atlantic Salmon populations, ecosystem effects (e.g. Friedland 1998) should be considered a threat for all DUs.

Table 3: Summary Assessment of Threats to Atlantic Salmon (in terms of salmon affected and lost to habitat alterations) for Proposed Designatable Units (DU) as Reported by Fisheries Managers

Proposed DU Atlantic Salmon Conservation Unit No. salmon rivers Salmon Affected: Spawners Lost
Regulated Habitat Alterations Other
Municipal waste water Industrial effluents
(pulp and paper, etc.)
Hydroelectric and
water storage dams
Water extraction Urbanization (hydrology) Transportation Infrastructure
(roads culverts and fish passage)
Aquaculture siting Agriculture, forestry. mining Dredging Cumulative Shipping transport Air pollutants / acid rain Ecosystem change
DU 2 1. North Labrador 28 L:L L:L L:L L:L L:L L:L L:L L:L L:L L:L L:L L:L LU:LU
DU 2 2. Lake. Melville Labrador 20 L:L L:L L:M L:L L:L M:M L:L L:L L:L U:U L:L L:L LU:LU
DU 2 3. South Labrador 41 L:L L:L L:L L:L L:L M:M L:L L:L L:L U:U L:L - : - LU:LU
DU 3 4. NE Coast NF 127 M:M L:L M:M L:L L:L M:M L:L M:M L:L U:U L: - - : - LU:LU
DU 4 5. SE Coast NF 49 L:L L:L L:L L:L L:L M:M L:L M:M L:L U:U U:U MU:MU LU:LU
DU 4 6. South Coast NF 55 L:L - :L M:M L:L L:L L:L M:M L:L L:L U:U - : - MU:MU LU:LU
DU 5 7. SW Coast NF 40 L:L L:L L:L L:L L:L U:U L:L M:M L:L U:U - : - - : - LU:LU
DU 6 8. NW Coast NF 34 L:L L:L L:L L:L L:L L:L L:L L:L L:L L:L L:L - : - LU:LU
DU 12 9. Northern NB 15 L:L L:L LM:LM L:L L:L M:M N/A M:M L:L M:M U:U L:U LU:LU
DU 12 10. Central NB 25 LM:L L:L L:L L:L L:L M:M N/A LM:L L:L M:M U:U L:U LU:LU
DU 12 12. NE NS 33 LM:LM L:L L:L L:L L:L M:M N/A L:L L:L M:M U:U U:U LU:LU
DU 13 13. CB East Highlands 8 M:L U:U L:L L:L H:U H:U H:U H:U L:L U:U H:U L:L H:U
DU 13 14. CB East Lowlands 21 H:U U:U L:L L:L H:U H:U H:U H:U L:L MH:U H:U L:L H:U
DU 14 15. NS Southern Upland 63 H:U L:L H:M U:U H:U H:U U:U H:U L:L H:U L:L H:H H:U
DU 15 16. iBoF NS/NB 37 H:U L:L M:L U:U H:U H:U H:U H:U L:L H:M L:U L:L H:H
DU 16 17. OBoF NB 17 H:U H:U H:M MH:U H:U H:U M:U H:U L:L H:M H:U U:U H:H
DU 12 18. Chaleur Bay PQ 5 L:L L:L N/A L:L L:L L:L N/A L:L - : - L:L - : - L:L L:L
DU 12 19. Gaspé Peninsula PQ 10 U:U U:U N/A N/A L:L L:L U:U U:U - : - L:L U:U U:U U:U
DU 12 20. Lower St. Lawrence N. Shore Gaspé PQ 9 L:L N/A L:L L:L L:L L:L N/A L:L - : - L:L - : - L:L L:L
DU 10 21. Appalachian Region PQ 0                          
DU 10 22. Quebec City Region PQ 3 L:L U:U U:U U:U U:U L:L U:U U:U U:U U:U U:U U:U M:M
DU 10 23. Saguenay-Lac Saint-Jean PQ 4 L:L U:U U:U U:U U:U M:U U:U -: - U:U U:U U:U U:U H:L
DU 8 24. Upper North Shore PQ 12 N/A N/A L:L L:L N/A N/A N/A UL:UL N/A - : - N/A N/A U:U
DU s 7,8 25. Middle North Shore PQ 17 N/A N/A L:L N/A N/A N/A N/A UL:UL N/A - : - N/A N/A U:U
DU s 2,7 26. Lower North Shore PQ 21 N/A N/A L:L N/A N/A N/A N/A N/A N/A - : - N/A N/A U:U
DU 9 27. Anticosti PQ 25 N/A N/A N/A N/A N/A N/A N/A U:U N/A - : - N/A N/A U:U
DU 1 28. Ungava PQ 4 L:L N/A N/A L:L L:L L:L L:L L:L L:L L:L U:U U:U U:U

(modified from DFO and MRNF 2009).
Dark shading highlights ‘>30% of salmon affected’; light shading is ‘5-30% affected’ and no shading is <5% affected-often not applicable unassessed, uncertain.

a- Where ‘salmon affected’ symbol ‘L’ is < 5% of salmon in DU are affected; ‘M’ is 5-30% are affected, ‘H’ is >30% are affected and ‘U’ is uncertain; ‘salmon lost’ symbol ‘L’ is < 5% of salmon spawners in DU are lost; ‘M’ is 5-30% are lost, ‘H’ is >30% are lost and ‘U’ is uncertain; N/A = Not Applicable and ‘-’  = Not Assessed.
*Cairns et al. 2009 state there were at least 22 salmon rivers in PEI.


xx Elements of this section have been copied, abstracted and/or synthesized from Cairns (2001), Dempson et al. (2008), COSEWIC (2006a, 2006b), DFO and MRNF (2008) and DFO and MRNF (2009).

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