Great Slave – Habitat & Species

Habitat & Species

Aquatic habitat and species in the Great Slave sub-basin are undergoing moderate change. Unhealthy fish with physical deformities and softer flesh and mass fish die-offs have been observed by many Indigenous communities. Populations of some fish species are declining, such as grayling (Thymallus arcticus) and suckers (Catostomus spp.) in the Mackenzie River, and inconnu (coney; Stenodus leucichthys) stocks near Yellowknife. Mercury and arsenic contamination affect fish populations in certain waterbodies near historical mine sites; however, in most places scientific data show that fish are safe to eat. Indigenous communities have reported new fish species rarely or never seen in the sub-basin, such as inconnu (coney) near Lutselk’e and salmon near Yellowknife. Documented scientific or Indigenous Knowledge observations of changes in wetland cover and riparian forests in the sub-basin are limited. However, some Indigenous communities have observed changes in wetland-dependent animal populations, particularly more variability in beaver (Castor canadensis) populations and a continued decline in muskrat (Ondatra zibethicus) abundance.

Information Availability

The following table summarizes the availability of information for each Habitat and Species indicator.

Signs and Signals	Indigenous Knowledge Information and Data	Indigenous Knowledge Availability¹	Science Information and Data	Science Data Availability²
Fish	Oral histories and local observations of fish abundance, timing and distribution, species diversity and fish health condition. Local observations about changes in timing of local fishing activity and yield.	Many observations from several locations.	Fish (including salmon, suckers, pickerels, burbot) abundance, timing and distribution, species diversity and fish health condition.	Data available.
Wetlands	Oral histories and stories of wetland and forest (and other habitat / land use) Local observations and oral histories of number, location and total area of wetlands	Some observations from few locations.	Number, location and total area of wetlands. Species diversity in wetlands where available.	Limited information on wetland cover and no information on change over time. Scientific information on muskrat and beaver populations was not gathered for this report.
Riparian Forests	Local observations and oral histories of riparian forests	No information found.	Number, location, total area of riparian forests areas. Species diversity of riparian forests where available.	Data only available for Alberta portion of Slave River watershed.

¹ Qualifiers for the availability of local and Indigenous Knowledge observations in publicly available sources: Limited = 1-2 observations; Some = 3-4 observations; Many = 5 or more observations
²Qualifiers for the availability of science data in publicly available sources: Low = Individual studies or locations; Many = Network of monitoring stations across the basin

Fish

Declines in fish populations and fish health condition have been observed by Indigenous communities in some areas in the Great Slave sub-basin. Contaminant levels in fish are safe for consumption according to scientific data, except in specific water bodies that are affected by historical mining impacts.

Indigenous communities have observed less healthy fish and fish die-offs

Changes in fish health condition and mass fish die-offs have been observed in some waterbodies in the Great Slave sub-basin. Instances of “soggy” fish and fish with softer flesh are recently reported by many Indigenous communities, including elders from Fort Smith and Fort Resolution, the Deh Gah Got’ie First Nation of Fort Providence, the Dehcho First Nations, and the Akaitcho First Nations.
Community members [from Deh Gah Got’ie First Nation] recall that, when the water is warmer, they are more likely to catch fish that are “soggy”. Fish caught in this state are not favored and, therefore, would not be eaten,
Guyot et al., 2006
Observations of softer fish are often linked to warmer water temperatures. Members of the Akaitcho First Nations and Dehcho First Nations report catching skinnier fish, fish with discoloured livers or stomachs, sores and other signs or signals of poor health condition. Elders from Fort Smith and Fort Resolution have observed an increase in sores and lesions present on fish caught in the Slave River and Delta in the past decade and describe that fish have a different taste. Fish die-offs have also been observed by many communities, including a die-off near Yellowknife at Wool Bay described by members of the Akaitcho First Nations.

In the 1990s fish in the Slave River were deemed safe for consumption

Studies in the 1990s indicate that fish populations in the Slave River at Fort Smith are safe for human consumption, because levels of organochlorine (OC) pesticides, PCBs, dioxin and furan isomers, polycyclic aromatic hydrocarbons, chlorinated phenolics, and heavy metals were low.

Indigenous communities have observed declines in certain fish populations, which is similarly reported in some scientific studies

Indigenous communities have observed some fish populations in the Great Slave sub-basin are in decline. A general decline in fish populations in the Slave River was noted in one study with Akaitcho First Nations members, including Smith’s Landing First Nation and Deninu Ku’e First Nation. Members from both communities observed that fish are having difficulty reaching spawning grounds in creeks and small rivers off the Slave River due to low water levels, affecting their ability to reproduce. Similarly, community members indicated that they historically caught inconnu (Stenodus leucicthys) in the Taltson River, likely during spawning migration, but that inconnu are no longer found in that river.

Akaitcho fishers also report a decline in coney stocks around Yellowknife, in areas where they used to fish. Declines in stocks of grayling (Thymallus thymallus) and suckers have been noted by members of the Dehcho First Nations, particularly in the Mackenzie River. A recent study showed a 70% decrease in Number of fish Per Unit Effort (NPUE: individuals/1000 m²/net set) and Biomass Per Unit Effort (BPUE: Kg/1000 m²/net set) over time in several areas of Great Slave Lake, which may point to a decline in fish populations.

Mercury and arsenic contamination in fish is a concern in water bodies affected by mining and hydroelectric development

Elevated levels of mercury, arsenic and related toxins affect fish populations in some waterbodies in the Great Slave sub-basin. Mercury contamination of fish in the area around Noncho Lake is suspected by Lutsel K’e Dene First Nation members, which is thought to be linked to flooding in the region for the Talston River Hydroelectric Project. There is particular concern [among Lutsel K’e Dene First Nation members] about how tailings water may be draining into downstream lakes such as Snap Lake and Gahcho Kue. The abandoned gold mines at Yellowknife on Great Slave Lake are a significant concern due to the presence of arsenic in the water (Yellowknife–Back Bay),
Parlee and Maloney, 2017
The potential for contaminated tailings water to drain into fish-bearing lakes, such as Snap Lake and Gahchoe Kue, and arsenic contamination in the Yellowknife-Back Bay area from abandoned gold mines near Yellowknife, are also a significant concern for the Lutsel K’e Dene. Scientific studies have found elevated concentrations of arsenic in fish tissues in fish collected near the Giant mine site in the early 2000s, suggesting the area continues to be a source of arsenic to aquatic ecosystems. Dehcho First Nations members have also recently expressed concern for elevated mercury concentrations in some fish species harvested in the Dehcho region of the Northwest Territories. Lake whitefish (Coregonus clupeaformis), northern pike (Esox lucius) and walleye (Sander vitreus) sampled over a three-year period in the early 1990s in Hay River (at mouth), Slave River at Fort Smith, and Leland Lake (in Slave drainage) showed no evidence of basin-related anthropogenic influence.

Great Slave Lake commercial fishery is the largest in the Northwest Territories but annual harvest has declined steadily

Great Slave Lake contains every fish species found in the Northwest Territories and is the largest freshwater commercial fishery in the region. Aboriginal subsistence and non‐Aboriginal domestic fishing are important activities of northern residents, and recreational fishing is significant to both residents and visitors.

The commercial fishery in the Northwest Territories is relatively small: ca. 1000 t/yr for the entire territory and Great Slave Lake accounts for roughly 90% of that. Significant commercial fishing on Great Slave Lake began in the mid-20th century but annual production has been in decline since the 1960s due to overharvesting and dwindling fish harvester participation. By the 1960s, lake trout (Salvelinus namaycush) harvest had collapsed due to overexploitation. Initially, lake trout was the main focus, although lake whitefish was also harvested. The lake trout population is currently still being managed through catch limits. There was no indication of a decline in lake whitefish stock status among management areas. However, information gaps and uncertainties in the assessment were identified. Inconnu had also declined as bycatch of whitefish harvest and as of 2012 was assessed as being in the “Critical Zone” of the Precautionary Approach model framework based on CPUE of mature female Inconnu. This means that the fish stock has been severely reduced, that stock management is focused on conservation and recovery and that fish harvest is limited to an absolute minimum.

Mercury levels in fish populations from Great Slave Lake are mostly within consumption guidelines

In one study, mercury levels in fish tissues were measured in fish caught at Resolution Bay, Great Slave Lake (burbot (Lota lota), northern pike) and in the Hay River (lake trout). Burbot and lake trout in the West basin all had low to medium mercury levels in 2017 and 2018. Northern pike had low levels of mercury, except for one individual above the 0.5 ppm guideline in 2018. Lake whitefish and suckers were found to have significantly lower mercury concentrations. As a result, the Government of Northwest Territories (GNWT) Health and Social Services Department did not issue specific consumption guidelines for fish harvested in Great Slave Lake. Fish from the east arm of Great Slave Lake were sampled in 2017 and 2018 from Lutsel K’e, NT, including burbot, northern pike, and lake trout. Low to medium levels of mercury were found in pike and burbot, whereas mercury levels in lake trout were more variable, with low, medium and high levels. One lake trout sampled was unsafe to eat according to the 0.5 ppm guidelines; the total number of fish sampled was not reported.

Indigenous communities have observed new fish species near Great Slave Lake

Some Indigenous communities have observed fish species rarely seen in the Great Slave sub-basin. Lutsel K’e Dene First Nation fishers have reported an increase in coney (inconnu) populations near Lutselk’e, NT, which are rarely seen in the region. Akaitcho fishers report catching more salmon in the Yellowknife area in recent years.

Wetlands & Riparian Forests

Riparian areas in the Alberta portion of the Slave River watershed are intact, but information on the remainder of the sub-basin as well as changes over time in wetlands and riparian forests in the Great Slave sub-basin is limited. Indigenous communities have observed changes in wetland-dependent wildlife species, including beaver and muskrat.

Indigenous communities have observed more variability in beaver populations

Beavers are generally considered by Indigenous communities to be more numerous in the Slave River Delta than in the past; however, some communities have raised concern for beaver population declines in localized areas. An increase in beavers and beaver dams in recent years on the Horn River has been reported by Deh Gah Got’ie First Nation members which they associate with the more variable water flow patterns observed in the Horn River watershed.

Indigenous communities have witnessed a decline in muskrat populations

A decline in muskrat abundance has been observed since the 1970s in the Slave River Delta by local Indigenous communities. In the past decade, many harvesters have observed it is increasingly difficult to find muskrats in the Delta.

Limited data on wetland cover

Wetland cover was mapped Canada-wide using satellite data but the data still requires validation.

Wetland Mapping for Great Slave Sub-basin as part of a Canadian Wetland Inventory that still requires validation*.

Intact Riparian Areas in the Alberta portion of the sub-basin

Riparian ecosystems in the Alberta portion of the Slave River sub-basin remain largely intact. There is very little development, as human footprint in the Alberta portion of the sub-basin is estimated to be 0.1%.

References

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