Biodiversity in Canadian Lakes and Rivers
- Trends in Freshwater Fish of Special Interest
- Trends in Hydrological Regimes
- Trends in River and Lake Ice Break-Up/Freeze-Up
- Trends in Habitat Loss and Fragmentation
- Trends in Pollutants in Lake and River Systems
- Future Climate Impacts on Lakes and Rivers
- Synthesis of Data
- Appendix 1
Trends in Freshwater Fish of Special Interest
Environmental and anthropogenic pressures have resulted in more than 20% of the world's freshwater fish becoming extinct, endangered, or threatened in recent decades--with some analyses stating that this is an underestimate (for example, Bräutigam, 1999). This section focuses on freshwater fish species and is necessarily limited in scope because of a general absence of data consistently collected or observed across the country for all taxa, including fish, and a general lack of national data for non-fish taxa. As of September 2010, the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) had assessed 18% (35 species) of freshwater and diadromous fishes as Endangered or Threatened throughout all or parts of their ranges. Fifty-eight species (29%) were assessed as at risk, which includes species assessed as Extirpated and of Special Concern, as well as those that are Endangered or Threatened (Hutchings and Festa-Bianchet, 2009; Hutchings, 2010; COSEWIC, 2010c). A 2008 compilation of imperilled freshwater and diadromous fish species in North America found that 89% had the same or worse conservation status in 2008 compared with a 1989 study that explored the same dataset (Jelks et al., 2008). Within freshwater ecoregions of Canada, the numbers of imperilled fish taxa increased from 12 in 1979, to 22 in 1989, to 62 in 2008 (Figure 3). Habitat degradation and introduced species were identified as the main threats to many species, many of which have restricted ranges (Jelks et al., 2008).
Source: adapted from Jelks et al. (2008)
Long Description for Figure 3.
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Chu et al. (2003) explored freshwater fish biodiversity in Canada in relation to environmental and stress metrics. Despite a lack of recent data, their results suggest that anthropogenic stresses and associated species introductions (either accidental or deliberate) were the major cause of extinction and extirpation in Canada. In addition, the authors note that the largely unmeasured effects of overexploitation of fisheries stocks, combined with the likely significant impacts of future climate change, would exacerbate these anthropogenic pressures.
For this report, a literature search of reports by COSEWIC (2010b) was completed to examine the threats causing individual freshwater fish species decline in Canada. Results suggest habitat degradation and loss, species introductions, siltation, dams and impoundments, and urban, agricultural, and industrial development are the main threats to freshwater fish species in Canada. Additional threats identified from the literature search include: water extraction, overexploitation, acid rain effects, channel modification, and contaminants. Six examples of freshwater fish species assessed by COSEWIC and listed under the federal Species at Risk Act have been selected to provide information about the impacts of anthropogenic threats on freshwater fish species. These species were chosen to provide examples of the different impacts affecting aquatic communities across Canada. We selected two populations of Atlantic salmon (both Inner Bay of Fundy and Lake Ontario), banded killifish, coho salmon (Fraser River), river redhorse, and white sturgeon as examples of at-risk fish communities affected by anthropogenic and natural habitat alterations (including climate variability and fragmentation), overexploitation, and the spread of invasive species.
Inner Bay of Fundy population of Atlantic salmon
Within the Atlantic Maritime Ecozone+, the Inner Bay of Fundy population of Atlantic salmon (Salmo salar) has been assessed as Endangered (COSEWIC, 2006b; COSEWIC, 2010a). Within this area, populations of Atlantic salmon have been under continuous threat since the 17th century from a range of human activities including dam construction, overfishing, overexploitation, and pollution. Occurring in New Brunswick, Nova Scotia, and the Atlantic Ocean, the historical population likely exceeded 40,000 adults. By contrast, the fall spawning estimate in 2003 was less than 100 adults in the 32 historically populated rivers (COSEWIC, 2006b) and estimates from 2008 put the total number of wild salmon at less than 200 (COSEWIC, 2010a). Examination of individual rivers within the inner Bay of Fundy demonstrates similar patterns. For example, the number of returns within the Big Salmon River dramatically declined by more than 96.7% over 30 years from a recorded peak of 5,043 (80% Bayesian Confidence Interval(BCIFootnote 7)=3,996 to 6,686) in 1966 to an estimated 55 (80% BCI=18 to 133) individuals in 2002 (COSEWIC, 2006b). Data from historical commercial fisheries from 1975 to 1984 highlight the dramatic decline of the catch of Inner Bay of Fundy Atlantic salmon. Despite the high inter-annual variability, the overall declining trend is clear, with the highest landings from 1875 to 1924, smaller landings from 1925 to 1973, and the lowest landings from 1974 to the closure of the fishery in 1985 (Figure 4). Although the reasons for population collapse are not completely understood, it is suggested that there has been reduced survival from smolt to adulthood in marine waters, potentially caused by community shifts through increased interactions with farmed and hatchery salmon, environmental shifts (increasing water temperatures), and fisheries (COSEWIC, 2006b). In addition, there has been a historical loss and degradation of habitat (for example, through logging and barriers to migration) (COSEWIC, 2006b). See the Atlantic Maritime Ecozone+ status and trends assessment (Eaton, 2013) for more information.
Lake Ontario population of Atlantic salmon
The Lake Ontario population of Atlantic salmon was assessed as Extirpated by COSEWIC in 2006 (COSEWIC, 2006a). Based on historical evidence, the population began a marked decline in the mid-1800s, with no observation of a wild Atlantic salmon within the watershed after 1898. The population collapse was likely caused by habitat destruction and overexploitation following the colonization of Upper Canada in the late 1700s (COSEWIC, 2006a). Despite recent efforts to restore habitat, restocking attempts have failed. Part of this may be attributed to the direct and indirect impacts of urbanization (including pollution, channelization, and loss of habitat) in the Greater Toronto Area (COSEWIC, 2006a).
Within the Newfoundland Boreal Ecozone+, the banded killifish (Fundulus diaphanus) has been assessed as Special Concern (COSEWIC, 2003a). Although widely distributed across North America, the Newfoundland population is threatened due to the limitations of population movement and range expansion because of steep gradients and impassable habitat, coupled with the risks associated with future logging operations (COSEWIC, 2003a).
Interior Fraser coho salmon
Interior Fraser coho salmon (Oncorhynchus kisutch) are a genetically distinct population of coho salmon that spawn and rear in the interior portion of the Fraser River watershed, north of Hope, BC. From 1975 to 2011, escapement of Interior Fraser coho declined 72% (Decker and Irvine, 2013), with the largest declines (in excess of 60%) occurring between 1990 and 2000 (Figure 5) (COSEWIC, 2002). Between 1975 and 1988, the number of spawners averaged 60,000, while only 9,000 spawners returned in 1996, the lowest year on record (Decker and Irvine, 2013).
Source: data from Decker and Irvine (2013)
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|Return Year||Total returns||Wild escapement||Wild + hatchery escapement|
Assessed as Endangered by COSEWIC in 2002, this population's migratory behaviour and habits make it susceptible to both natural and anthropogenic impacts (COSEWIC, 2002). Declines during the 1990s were attributed to declining marine survival exacerbated by overfishing, but escapement has also remained low in the 2000s compared to pre-1991 levels (Decker and Irvine, 2013). From 2001 to 2011, there have been four years where production of returning spawners was below replacement levels, even in the absence of fishing (Decker and Irvine, 2013). However, average escapement from 2009–2011 was estimated at 27,000, indicating some recovery has occurred (Decker and Irvine, 2013). In general, escapement has increased gradually across the five conservation units (CUs) that make up the range of interior Fraser coho with the exception of the Lower Thompson CU, which has seen a larger 72% increase in escapement, and the Fraser Canyon CU, which has seen a 58% decrease in escapement (Figure 6 ) (Decker and Irvine, 2013). Key threats to the long-term survival of interior Fraser coho continue to be fishing and habitat perturbations, as well as climate change (Decker and Irvine, 2013).
Data for the Lower Thompson CU prior to 1984 and for the Mid/Upper Fraser and Fraser Canyon CUs prior to 1998 are extrapolated based on observed escapements for the other units. Exploitation rates for 1975–1985 are the average of estimates for 1986–1996. See Decker and Irvine (2013) for further details.
Source: data from Decker and Irvine (2013).
Long Description for Figure 6.
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|Return Year||South Thompson||North Thompson||Lower Thompson||Mid/Upper Fraser||Fraser Canyon|
The Canadian range of the river redhorse (Moxostoma carinatum) includes areas of southern Ontario and Quebec and has been threatened because of habitat degradation (such as pollution and siltation), stream regulation from dams, and habitat fragmentation (COSEWIC, 2006c). Assessed as Special Concern by COSEWIC, populations have been lost from the Ausable, Châteauguay, Noire, and Yamaska rivers but were still present in the Mississippi, Ottawa, and Richelieu rivers in 2004 (COSEWIC, 2006c). The river redhorse was common in the 1940s in the St. Lawrence River but has markedly decreased since then in that system through fragmentation from canal diversions and dam developments (COSEWIC, 2006c).
White sturgeon (Acipenser transmontanus), the largest freshwater fish in Canada, is restricted to the west coast of North America (Welch et al., 2006). Its size (up to 6 metres), longevity (over 100 years), and late maturity (14 to 30 years), make it especially vulnerable to overexploitation and habitat degradation (COSEWIC, 2003b). Populations of white sturgeon have substantially declined in Canada over the last century (COSEWIC, 2003b). Of the six white sturgeon populations in BC, three are declining (Columbia, Kootenay, Nechako), one is now more stable, with some fluctuations (lower Fraser), and two are stable (mid- and upper Fraser) (COSEWIC, 2003b; McAdam, 2009, pers. comm.).
Poor juvenile survival, linked to river diversions, changes in sediment quantity and quality, and water flow regulation associated with dams, are the primary reasons for endangerment of the three declining populations (COSEWIC, 2003b; McAdam et al., 2005).These declining populations are projected to decline by more than 83% in the next generation, although conservation efforts including hatchery spawning and release of juveniles are being carried out to attempt to mitigate this decline (COSEWIC, 2003b).Juvenile production (or recruitment) of the Nechako River population illustrates this trend (Figure 7). Recruitment failure of the Nechako population is hypothesized to result from altered substrates in the river, particularly following two slide events that collectively added 1 million m3 of silt, sand, and fine gravel into the main channel, with roughly half of this material subsequently moving downstream (McAdam et al., 2005).
- Footnote 7
BCI = Bayesian Confidence Interval
- Date Modified: