Wildlife

The Northwest Territories is one of the few remaining regions in the world with herds of wild migratory caribou, muskoxen, healthy populations of top predators, and rich northern biodiversity. Wildlife is one of the main links between people and the environment.

The indicators presented in this chapter reveal changes occurring in NWT wildlife. Some northern wildlife species experience large natural fluctuations in population numbers over time. These population cycles are the “heartbeat” of NWT ecosystems. A change or a decline in these cycles could indicate a change in the environment that should be examined. Two indicators that track population cycles are provided in this chapter.

Other indicators on selected species provide information on status and trends in different ecozones of the NWT. Caribou are a major focus species, and one indicator pf the indicators provides information on barren-ground caribou populations. Indicators on birds and fish provide information on changes and declines for these groups of species of particular importance to NWT people. Information on winter tick, a parasite that affects moose populations, is provided as an indicator of wildlife health. Other factors influencing wildlife heath are presented in the CONTAMINANTS focal point.

Trends in the number of new species in the NWT, as well as species that are expanding their ranges to new areas within the NWT are tracked as such changes are predicted to occur with a warming climate.

The indicator tracks population numbers of willow ptarmigan and three species of grouse: spruce grouse, sharp-tailed grouse, and ruffed grouse. These are all major prey species in NWT tundra and taiga ecosystems.

Willow ptarmigan nest on the tundra, and perform a mini migration to just below the treeline – on the taiga – every winter. Other species of ptarmigan occur in the NWT but are not part of this indicator: Spruce grouse are present year-round in forested parts of the NWT. They are most numerous in coniferous forests. Ruffed grouse and sharp-tailed grouse are also year-round residents and are most numerous in the taiga plains, mostly in deciduous forests as far north as the Sahtu.

The information for this indicator is obtained from the Christmas Bird Count (CBC)³² a volunteer-based program with count sites across North America, including in the NWT, and from the NWT Resident Hunter Survey.

NWT Focus

This indicator offers insight into changes in small-sized prey populations in NWT ecosystems. Grouse numbers do not cycle everywhere in their range in North America. Cycles of about 10 years are recorded only in populations in the NWT, as well as other northern populations in Yukon and Alaska²⁶. Tracking cycles in ptarmigan and grouse populations in NWT ecozones, and comparing these to other 10-year cycles such as snowshoe hare cycles (see Trends in small mammals and hares in NWT ecosystems), help increase our understanding of annual changes in the availability of medium-sized prey species, and changes in behaviour, dispersal, and productivity of NWT’s predator species.

Current view: status and trend

All ptarmigan and grouse species tracked in the NWT show large fluctuations in numbers. Willow ptarmigan numbers seem to fluctuate every 10 years or so. Numbers were high around 1985, 1996-1997 and 2006-2007. This 10-year cycle is most apparent in the 20-year dataset from the Christmas Bird Count in Yellowknife. This cycle is also reflected in the hunting success of NWT resident hunters.

Ptarmigan: number of ptarmigan observed per group of birders (party) per hour on one day within one week of Christmas day, as part of the Christmas Bird Count program. Ptarmigan and grouse: number of birds estimated killed by resident hunters during a hunting season as recorded by hunting questionnaires. Source: ENR Resident Hunter Surveys and Christmas Bird Counts, Birds Studies Canada and National Audubon Society.

A similar cycle, apparently synchronized with willow ptarmigan, can be detected using the resident hunter survey data for spruce grouse, ruffed grouse and sharp-tailed grouse.

These large-scale synchronized population fluctuations suggest ecosystem-level causes may be at work, such as climatic fluctuations³⁹ or changes in predator numbers linked to changes in other prey species such as snowshoe hares²⁶. These hypotheses still require study. In the NWT, ptarmigan and grouse numbers started to peak during the decadal low in hare numbers (1995, 2005; see Trends in small mammals and hares in NWT ecosystems), then declined sharply during the year when hare also declined. Why this occurs is unknown. There is little NWT data to track the effects of these large fluctuations on most predator numbers.

Looking forward

If the current pattern continues, the next peak in population numbers for grouse and ptarmigan should occur around 2016-2017. Differences in the timing of peak numbers of ptarmigan and grouse in different regions of the NWT may be tracked as more information is gathered using the CBC, hunter surveys, and local knowledge.

Looking around

Cycles in numbers every 10 years have been noted for willow ptarmigan, spruce grouse, and ruffed grouse in Yukon²⁶, for Alaska spruce grouse in Alaska²⁶, and for rock ptarmigan in Norway. In Yukon, numbers of grouse increased slightly (1-2 years) before peaks in snowshoe hares²⁶. In the NWT, both grouse and ptarmigan numbers peaked in the middle of the lows in snowshoe hare populations. These regional differences remain unexplained.

Find out more

• To find more on ptarmigans and grouse, go www.enr.gov.nt.ca.
• For more information on the Christmas Bird Count go to www.audubon.org/bird/cbc/index.html and Birds Studies Canada.

Other focal points

• See NATURAL CLIMATE FLUCTUATIONS and CLIMATE and WEATHER for indicators on weather-climate events that may drive or influence population cycles in northern species.  

Technical Notes

• More information on the resident hunter survey can be found in references below.
• Raw data from the CBC can be downloaded from http://www.audubon.org/bird/cbc/index.html .
• Raw data from the resident hunter survey are available under request from ENR.

Updated: 20 December 2012

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15.2 Trends in small mammals and hares in NWT ecosystems 

This indicator tracks population numbers of small mammals and snowshoe hare, major prey species in NWT ecosystems.

The information for this indicator is obtained from the NWT small mammal survey³⁷ and the NWT hare transect survey. The small mammal survey (SMS) is designed to monitor changes in vole, mouse, lemming, and shrew abundance across five ecozones in the Northwest Territories, and to link with similar a survey in Nunavut²⁷. The hare transect survey (HTS) is designed to monitor changes in hare numbers across three forest ecozones in the Northwest Territories. This monitoring provides information on predator (furbearer) abundance to trappers. Lynx is the main predator of snowshoe hare.

NWT Focus

Small mammals and hares play a keystone role in both arctic and boreal ecosystems²⁵. They are major prey species for foxes, marten, lynx, raptors, and other carnivores. Cyclic fluctuations in their abundance are reflected in similar fluctuations in the abundance of their predators^{19, 25}. The effects of low abundance in small mammal numbers can also affect alternative prey species such as duck eggs³⁵. When hares are scarce, foxes and other predators will spend energy on alternative, harder to find food sources, such as waterfowl nests. A sharp decrease in waterfowl productivity has been measured in NWT taiga ecosystems in years of low hare density. A 10-year cycle in whooping crane productivity has been recorded in which years of low whooping crane productivity match years of low hare numbers⁶.

Small mammal/hare density and trend information is used in predicting population trends of economically important furbearers and in monitoring natural changes in predator/prey relationship in northern ecosystems. NWT residents have noticed that foxes are more likely to enter communities when hares and small mammals are low.

The small mammal species tracked in the NWT differ for each ecosystem. In forested regions, small mammals include deer mouse, meadow vole, southern red-backed vole, and northern red-backed vole. On the tundra, small mammals include collared lemming and brown lemming. Snowshoe hare are found in all forested regions of the NWT.

Current view: status and trend

Small Mammals

Small mammal populations fluctuate in numbers at most sites surveyed. Peaks in small mammal numbers occur in different years in different regions. There is not enough information to determine if there are similar cycles in the Inuvik area (northern Taiga Plains). Small mammal fluctuations at the only site on the tundra in the southern Arctic (Daring Lake) do not appear to be in synchrony with any sites in forested NWT. Data from surveys performed in Nunavut in 1987-2001 suggest that the Daring Lake site matches fluctuations measured in other areas of the barrens (i.e., Baker Lake).

Hare: Number of pellets counted on permanent transects cleared every year in June (exceptions in timing exist). Pellet counts are transformed to an estimate of hare density - hare per hectares - using a regression developed over 20 years in Yukon. Source: NWT Hare Survey

Snowshoe hare can reach very high densities every 10 years or so. Trappers have reported that the past two peak densities in hares have not been as high as in the 1970s. Based on information from the past three cycles, it appears that peaks in numbers occur in slightly different years in different regions. Little evidence for hare population cycles has been detected in the extreme southwest portion of the NWT (site in Dehcho). Flooding in some years at this site may explain this.

Hare and Lynx: Hare density as in Hare graph. Number of lynx pelts sold at auctions. Source: NWT Hare Survey and ITI Fur Database.

The 10-year cycle in hare numbers is strongly reflected in lynx fur sale records. The strong relationship in the 10-year cycles in snowshoe hare and lynx have been studied for about 100 years. These reasons for the 10-cycles are proving more complex than anyone anticipated. The explanation⁴⁰ that best fits with observations and ecological mechanisms involves a decline in food availability as hare populations go up. When hare density is very high, increased diseases and predation by lynx results in a rapid crash in hare numbers. The timing and synchronization of these cycles across large parts of North America are best explained by large weather fluctuations such as the North Atlantic Oscillation^{41, 42} and the El Niño Southern Oscillation⁵². Weather patterns may influence these cycles in many ways. For example, the type and total amount of snowfall may affect the ability of lynx to successfully hunt hare⁴³.

Looking forward

It is difficult to predict when peaks in numbers of small mammals will occur in the future. Snowshoe hare numbers peaked near 2010. An increase in hare numbers has been noted in most regions of the NWT, followed by a decline. This last peak in numbers again did not appear as large as those seen in the 1970s and earlier. The reasons for this are unknown.

Looking around

Cycles or fluctuations in small mammal numbers have been recorded in most northern ecosystems, including in other jurisdictions in North America, Scandinavia, northern Europe, northern Russia^{3, 8, 19, 26, 38}. The 10-year cycle in hare numbers is one of the best-known ecological phenomena in northern ecosystems^{9, 26, 40}. These cycles provide a pulse of extremely high numbers of prey available to a small set of northern predators. There is evidence that the 10-year cycle in hare density decreases or disappears in regions where hare habitat has been severely fragmented⁴⁹. As in the NWT, small mammal and hare cycles or fluctuations are often found to be synchronized over large regions^5,42. A greater synchrony is found within regions experiencing the same climate variability^{5, 25, 33, 40, 41}.

There is increasing evidence from northern Europe that small mammal cycles can collapse quickly and populations can reach permanently low levels if some climate conditions, such as the length of winter, change²². Long-term monitoring of small mammals and hare in the NWT is essential to detect whether or not similar collapses occur in the NWT.

Find out more

• To find more on small mammal and hare surveys in the NWT, go www.enr.gov.nt.ca.
• To find more information on what drives the hare cycles go to references below⁹.

Other focal points

• See NATURAL CLIMATE FLUCTUATIONS and CLIMATE and WEATHER for indicators on weather-climate events that may drive or influence population cycles in northern species.
• See indicators on USE OF RENEWABLE RESOURCES for more information on hunting statistics.

Updated: 20 December 2012

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15.3 Trends in Dall’s sheep in mountain ecosystems

This indicator tracks population and condition indices of a large herbivore in NWT’s mountain ecosystems, the Dall’s sheep.

Population indices include population densities and the number of lambs per 100 ewes. The condition index is the annual average horn growth in rams. These indicators may help monitor fluctuations in wildlife disease and parasite loads, and changes in carrying capacity due to climate changes in NWT mountain ecosystems.

Dall’s sheep demographics are measured using aerial and ground surveys performed at irregular intervals²⁹. Additional data on demographics are obtained from annual outfitter reports and hunter questionnaires³⁰. Horn growth rates are obtained from data collected with the help of hunters in both NWT and Yukon²¹. The interpretation of this indicator is enhanced by the local knowledge of hunters and users of NWT’s mountain ecosystems.

NWT Focus

Dall's sheep are found in Alaska, the Yukon, the western NWT and extreme north-western British Columbia. They are a hunted species. Sheep share NWT’s mountains with other large herbivores, including mountain caribou, moose and in some areas, mountain goat.

Current view: status and trend

Demographics

The number of Dall’s sheep in the Mackenzie Mountains is estimated at 15,000 - 26,000. Another population of about 700 further north in the Richardson Mountains was surveyed in 2006⁴⁴. Sheep have not been systematically surveyed in most of their range in the NWT, so trends in density are unknown. Densities are relatively low⁴⁷ compared to Yukon, and vary between 20 and 50 adults per 100 km^{2  15} .

Source: Density (ENR); Ratio of lamb/100 ewes from Larter and Dallaire, hunters’ observations; Condition horn index from D. Hick, pers. comm. Detailed information available.

The number of lambs per 100 ewes has changed little since 1995. Source: ENR.

Condition

Horns in male Dall's sheep grow each year. The growth rate differs with age and with the general condition of the animal. Looking at the difference between actual horn growth and average horn growth expected at each age gives insight into the general condition of rams in an area. Their condition or health is a result of a combination of food availability, weather, and previous year's condition. The mean deviation on horn growth in rams in the Mackenzie Mountains shows a cycle of good and bad years. Low growth occurred in 1990-1991 (probably also earlier), and again in 1997-2000 (Hik, pers. comm.). High growth occurred in 1993 - 1996.

Muscleworm (Paralephostrongylus odocoilei) and lungworm (Protostrongylus stilesi), parasites known to infect mule deer and sheep, have recently (2001) been found in populations of Dall’s sheep in the Mackenzie Mountains. These parasites can severely affect the lungs and muscles of infected sheep and reduce their survival. The life-cycle of the parasites are involve another species: the parasite larvae are shed in the feces of the sheep, invade a terrestrial snail where it develops over more than one year into other larvae stages, and infects other sheep when they feed on these infested snails with the vegetation²³. The length of the growing season affects the availability of these parasites to sheep. Transmission of the parasites occurs in the fall and a warming climate may increasing the time period in which the larvae in the host snails are available for infection, increase the number of larvae in infected snails, and increase the number of years with development of the larvae occur in only one year²³. A changing climate may result in increases in parasites in populations already infected and in expansion into populations not yet affected²⁸.

Looking forward

Northern herbivores are well adapted to harsh climate and to large changes in their environment. Large fluctuations in climate and quality of foraging habitat in NWT’s mountain ecosystems are not surprising. Dall’s sheep populations in the NWT have adapted to these fluctuations and appear to be healthy. The incidence of muscular and respiratory pathology due to parasites and diseases in Dall’s sheep is being tracked using samples collected by hunters and sent for analysis by ENR.

Looking around

Similar fluctuations in deviation of horn growth from the mean have been noted in Yukon. Over 31-years (1969-1999), Yukon data showed a '10-year' cycle in horn growth²¹ Possible causes for these annual differences in ram condition include regional fluctuations in climate, such as precipitation and temperature cycles, which in turn may influence abundance or timing of availability of food for sheep.

Interestingly, fluctuations in numbers of Dall’s sheep lambs have been correlated to the snowshoe hare cycles in Sheep Maintain, Yukon⁴⁸. Low lamb numbers occur about 1-2 years after the crash in hare numbers every 9-10 years. This may occur because generalist predators, such as golden eagles, that prey on both hares and sheep lambs, may heavily hunt lambs when hares are less abundant (the "Alternative prey" hypothesis)⁴⁸. It is not known if such a phenomenon occurs in the NWT.

Find out more

• To find more on Dall’s sheep, go to www.enr.gov.nt.ca.

Other focal points

• See NATURAL CLIMATE FLUCTUATIONS and CLIMATE and WEATHER for indicators on weather events that affect Dall’s sheep.
• See Trends in wildlife diseases in WILDLIFE for more information on other causes of variations in Dall’s sheep condition and demographics.
• See indicators on USE OF RENEWABLE RESOURCES for information of Dall’s sheep hunting.

Technical Notes

• Estimated of number of lambs per 100 ewes are obtained from hunter questionnaires provided from each of the 8 licensed outfitters for big game harvested in the Mackenzie Mountains each hunting season.
• Estimated volumes for annual horn growth increments are based on measurements of annual horn segment lengths and their annual base circumferences.

Updated: 20 December 2012

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15.4 Trends in barren-ground caribou population size in tundra-taiga ecosystems

This indicator measures the trend in population sizes of barren-ground caribou (Rangifer tarandus groenlandicus) herds in the NWT. Information on Peary caribou (R. t. pearyi) and boreal caribou (R.t. caribou) is presented in the Species at Risk focal point.

Population estimates are calculated and tracked to monitor the status of caribou herds (size and whether a herd is increasing, stable, or declining).

Barren-ground caribou in the NWT, as in Alaska and other jurisdictions, are managed at the herd level, with herds defined by fidelity to distinct calving grounds. Nine migratory caribou herds have part or their entire range in the NWT: Porcupine, Tuktoyaktuk Peninsula, Cape Bathurst, Bluenose-West, Bluenose-East, Bathurst, Beverly, Ahiak and Qamanirjuaq.

For large NWT barren-ground herds like the Beverly and Bathurst, population estimates are derived from photographic surveys in June when female caribou are concentrated on the calving grounds. Prior to the early 1980s, calving ground surveys were visual, but photographic surveys were found to be more accurate, particularly for counting larger groups of caribou. Caribou in smaller NWT herds like the Tuktoyaktuk Peninsula, Cape Bathurst, Bluenose-West and Bluenose-East herds, as well as most Alaskan herds, are counted from aerial photographs taken over large post-calving aggregations that form for insect relief.

The information for this indicator is obtained from ENR surveys that are conducted by biologists, with involvement of community members and in partnership with neighbouring wildlife agencies. Surveys of the Beverly, Ahiak and Qamanirjuaq herds are led by the Government of Nunavut.

NWT Focus

Caribou are an important source for food, clothing, and cultural identity for Aboriginal people in the NWT, and one of the NWT’s most important wildlife resources.

Some factors that affect caribou are difficult to control (e.g. weather) but human activities such as hunting and industrial development can be managed. When herds are declining or at low numbers they are less resilient to environmental change and hunter harvest than when herds are increasing or at high numbers. This information allows managers and users to identify which management actions are appropriate to ensure that caribou harvesting remains sustainable.

Current view: status and trend

Recent barren-ground caribou surveys indicate that Tuktoyaktuk Peninsula, Bluenose-West, Bathurst, Beverly and Qamanirjuaq herds are declining, the Cape Bathurst herd remains small but stable, and the Bluenose-East herd are stable¹⁷.

Porcupine herd Not shown on map. Range is west of the Mackenzie River. Share with Yukon and Alaska.  Numbers are from Alaska Department of Fish and Game, and Yukon Department of Environment.
Tuktuyaktuk Peninsula herd Shown on map in brown. Error bars are 95% CI.  Numbers are from ENR, GNWT, estimated based on post-calving surveys.     Note the difference in herd size with the much larger Porcupine herd.
Cape Bathurst herd Shown on map in green. Error bars are 95% CI.  Numbers are from ENR, GNWT, estimated based on post-calving surveys.   Note the difference in herd size with the much larger Porcupine herd.
Bluenose-West herd Shown on map in yellow. Error bars are 95% CI.  Numbers are from ENR, GNWT, estimated based on post-calving surveys. Note that prior to 2000, Bluenose-west and Bluenose-east were estimated together.  Population estimates for Bluenose-west prior to 2000 were re-calculated in 2008 using raw data.
Bluenose-east herd Shown on map in red. Error bars are 95% CI.  Numbers are from ENR, GNWT, estimated based on post-calving surveys. Note that prior to 2000, Bluenose-west and Bluenose-east were estimated together.  Population estimates for separate Bluenose-east prior to 2000 are not available.
Bathurst herd Shown on map in blue. Error bars are SE.  Numbers are from ENR, GNWT, estimated based on calving survey surveys.
Beverly herd Shown on map in pink. Error bars are SE.  Numbers are from Government of Nunavut and ENR, GNWT, estimated based on calving survey surveys.   No population estimate is available for the Beverly since 1994, however calving distribution surveys show a rapid decline between 2002 and 2007, and there were very few caribou on the traditional Beverly calving ground by 2009. The remainders of the collared Beverly females have been using the same calving grounds of the Ahiak herd (shown in pink on the map above). The Ahiak herd population number has been estimated only once, in 1996, using only four transects in the Queen Muld Gulf are, at which time the population numbered about 200,000 animals. Current numbers for the Ahiak herd are not available, but calf-cow ratio surveys in the 2000s have shown that the Ahiak herd was in decline during that period.  The next survey for the Ahiak/Beverly herds is planned for 2011 by the Government of Nunavut.  Results are pending.
Quamanirjuaq herd Not shown on map. Error bars are SE.  Numbers are from Government of Nunavut, estimated based on calving survey surveys.

Graphs: Population survey estimates for barren-ground caribou herds in the NWT, 1982-2010.

There are many natural factors that can influence population changes in caribou, including insect harassment, quality of forage in spring, summer and fall, depth of snow in winter, levels of predation, and other climate and range dynamics. Traditional and scientific sources provide evidence of caribou populations naturally increasing and decreasing on a periodic basis. These changes may be due to the influence of fluctuating climatic patterns^{13, 51}.

Human activities on barren-ground caribou ranges have changed in the last sixty years (see focal point Human Activities). Oil and gas exploration and development, as well as mineral exploration and mining, occur to varying degrees across barren-ground caribou ranges. Human harvesting patterns have also changed from dispersed harvesting to more concentrate harvesting in areas near communities or with improved road access to caribou. Winter roads have made remote areas more accessible, and technologies such as snowmobiles, aircrafts and all-terrain-vehicles (ATVs) have all changed how caribou are hunted.

The cumulative impact of these human activities on caribou herds is not well understood, but it must be assessed in the context of continuing natural variation in weather and foraging conditions.

Looking forward

When caribou herds are in decline, management actions take on greater significance. Declining or small herds are less resilient to hunting and disturbance than herds that are increasing or larger. The overall goal is to manage activities  that humans can influence (e.g., harvesting, resource development) so that herds can recover from natural declines¹³. Due to widespread community concerns over declining barren-ground caribou herds, the NWT produced a 5-year strategy (2006-2010) for increased barren-ground caribou monitoring and management actions. Management and monitoring strategies are described in the publication “Caribou Forever: Our Heritage, Our Responsibility”¹³. The strategy is being updated. As of May 2011, "A Barren-ground Caribou Management Strategy for the Northwest Territories for 2011-2015" is available review¹⁶.

Looking around

Caribou herds (both barren-ground and Peary) have declined in the past decades in most of northern North America¹⁸. Caribou herds increased from lows in the mid-1970s to peaks in the 1990s, and declined in the 2000s. However, exceptions can occur to this pattern. For example, the time of declines and peaks may be different in some Alaskan and northern Quebec herds. The Leaf River herd in Quebec/Labrador has increased while the neighbouring George River herd¹.

Source: Data from the Circumpolar CircumArctic Rangiver Monitoring and Assessment (CARMA), based on a technical report by Gunn and Russell (in press). Updated to 2010.

Find out more

• For more information on Canadian biodiversity: ecosystem status and trends 2010 go to www.biodivcanada.ca     
• For more information on CARMA go to http://carmanetwork.onconfluence.com/display/public/home
• Caribou Forever – Our Heritage, Our Responsibility at  http://www.nwtwildlife.com/pdf/CaribouMgmtStrategyFINAL060130.pdf
• Porcupine Caribou Management Board http://taiga.net/pcmb/harvest.html
• Beverly and Qamanirjuak Caribou Management Board http://www.arctic-caribou.com/

Technical Notes

• Data prior to 1980s was collected visual surveys. Photographic surveys were used from the 1980s onward.

Updated: 20 December 2012

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Change in wildlife distribution

15.5. Trends in range expansions of mammals

The indicator tracks mammal species that are extending their range in the NWT.

This indicator uses the information collated from NWT residents and visitors. This information is also used to track the status of mammals in the NWT General Status Ranking Program. The indicator helps track mammals that are new to the NWT and expanding using three categories:

NWT Focus

There are a greater number of mammals present further south than in the North. Change in the northern environment may favour expansion of these species into our ecosystems. Changes in species composition in an NWT ecoregion provide an indicator of ecosystem change, including habitat and climate change.

Official species lists have been compiled for the NWT General Status Ranking Program⁵⁰ since 2000. Species lists include all mammals. Updates on the range expansions of mammals in the NWT are only possible due to the contribution of NWT residents and visitors interested in NWT biodiversity.

Current view: status and trend

Source: Information from the NWT General Status Ranking Program and as referenced.

Looking forward

As people report species of mammals that they have rarely seen, or never seen before, the knowledge on NWT mammals and their distribution is increasing. Overall, it appears that some species are seen further north than before. This slow movement northward is not occurring at a constant rate. Some years more observations of range expansions are reported than in other years. This may be due to a variety of reasons such as milder winters, hot summers, and increased reporting. Vagrancy, where animals are seen a long distance from where they normally occur, is normal in mammals. Individuals, especially young ones, will try new territories and explore new habitats, and can travel further than expected. It remains difficult to detect when there is an increase in vagrancy and when populations are established in a new area, hence to detect a range extension. ENR personnel and interested community members in the North have a great role to play in monitoring range extension by recording and reporting details on animals that are “out of place”.

Find out more

• Find out about vagrant birds from the NWT/Nunavut Bird Checklist Survey at http://www.mb.ec.gc.ca/nature/migratorybirds/nwtbcs/index.en.html
• For more information on the NWT General Status Ranking Program go to www.nwtspeciesatrisk.ca

Other focal points

• See CLIMATE and VEGETATION for other indicators related to climate and new species of plants in the NWT.

Updated: 20 December 2012 

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15.6 Trends in number of introduced and alien mammals, birds and fish

This indicator tracks introduced and alien mammals, birds, and fish in the NWT. These species are best known and most studied.

Fish introductions, or stockings, have been used in the NWT to enhance the fishing potential of a small number of lakes, providing greater opportunities for sport fishing near roads.

Some species of domesticated mammals and birds, imported from Europe and Asia, are an important source of food and have been introduced in the NWT as part of our small but growing agriculture industry or as part of tourism operations. This indicator does not track the number of animals and birds that are kept in captivity for these purposes. This indicator tracks only introduced or alien species that are not captive, and that can survive in NWT's ecosystems without continuous care by humans. Past introduction of species that are not still present in the NWT are noted, but are not part the indicator. The indicator helps track mammals and birds that are not native to the NWT using three categories.

This indicator uses information collated from NWT residents and visitors. This information is also used to track the status of mammals, birds, and fish in the NWT General Status Ranking Program.

NWT Focus

Changes in the number of alien mammals and birds are monitored as their presence and abundance may affect the status of wild species native to the NWT. Official species lists have been compiled for the NWT General Status Ranking Program⁵⁰ since 2000. Species lists include all mammals and birds. Updates on introduced alien species in the NWT are only possible with to the contribution of many NWT residents and tourists interested in NWT biodiversity.

Current view: status and trend

One mammal and three bird species have been introduced in the NWT and are still present today.

Horses have been introduced to the NWT, but they are not included in the list of introduced species as all six were geldings. They were surviving with bison north of Fort Providence in late 1980s and early 1990s. Only one was still alive in 2007. These animals apparently escaped from captivity⁵⁰. In addition to horses, wild boar (Sus scrofa) was released as part of a sport hunting venture in 1996-2000. By 2000, these animals were captured and rapidly moved outside the NWT. In 2010, one animal was seen near Enterprise. It is unknown if this animal is a recent escape, and if it is part of a large group.

In 1935, after a five-year trek from Nome, Alaska, 2,370 reindeer arrived in the Mackenzie Delta³⁴. Reindeer can still be found on the Tuktoyaktuk Peninsula today. Reindeer are the same species as caribou (Rangifer tanrandus), so they are not included in the list of introduced mammals, but these particular animals (i.e., subspecies) are not native to the NWT.

Alien bird species were introduced to North America and are not part of NWT’s list of native bird species. They probably spread to NWT towns on their own.

All fish introductions were carried out as part of stocking initiatives Other than rainbow trout and introduced arctic char, attempts to stock other species of freshwater fish in lakes in the NWT have failed. There were attempts to introduce brook trout (Salvelinus fontinalis) from Alberta into Seven Mile Lake (1949) and Little Buffalo River (1960-61)¹¹. Cutthroat trout (Oncorhynchus clarki) and splake (Salvelinus namaycush x Salvelinus fontinalis), a hybrid between Lake trout and Brook trout, were introduced into Seven Mile Lake (1964), but were also unsuccessful¹¹. Brook trout (or splake) was also introduced into Polar Lake (1971), but is not present there today¹¹. These introductions are noted here for completeness, but are excluded from the indicator (see table below) as they did not result in viable populations.. Fish stocking has not occurred in NWT since 1990.

Source: Information from the NWT General Status Ranking Program and as referenced.

Looking forward

Some wildlife species thrive near humans. The number of introduced or alien mammals and birds is expected to increase as human population increases in the NWT and as habitats become fragmented and disturbed because many species introduced by humans survive better near communities or in habitats created by humans. The number of alien or introduced mammals, birds, and fish in the NWT is very small compared to other jurisdictions in southern Canada and the U.S. Our climate makes survival in NWT’s ecosystem a challenge unless species are adapted to the North or humans provide some help in the form of shelter and food. As NWT's winter climate becomes milder, all residents have a role to play in preventing unintentional releases of mammals, birds, and fish that may become naturalized and negatively affect NWT's ecosystems.

Find out more

• For more information on the NWT General Status Ranking Program go to www.nwtspeciesatrisk.ca 

Other focal points

• See CLIMATE for other indicators on climate in the NWT.
• See VEGETATION for indicators related to alien vascular plants in the NWT.
• See HUMAN ACTIVITES and LANDSCAPE CHANGES for indicators on short-term and long-term changes to ecosystems that result in increased number of alien or introduced mammals, birds and fish.

Updated: 20 December 2012

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References

Ref 1. CARMA Herd profiles. 2009. CAFF (Arctic Council). Available at http://yukon.taiga.net/carma/herds.html.

Ref 2. Afton A.D., Anderson M.G. 2001. Declining scaup populations: a retrospective analysis of long-term population and harvest survey data. Journal of Wildlife Management 65:781-796.

Ref 3. Bird Studies Canada. 2008. Common insect-eating birds suffer dramatic declines. Bird Studies Canada. BirdLife International.

Ref 4. Blancher P. 2003. The importance of Canada's boreal forest to landbirds. Canadian boreal initiative and the boreal songbirds initiative.

Ref 5. P. Blancher, B.D. and C. Collins. Land bird Trends for Arctic EcozonePlus (BCR 3) for Canadian Biodiversity: Ecosystem Status and Trends Report. Available at http://biodivcanada.ca.

Ref 6. Bob Decker. 2001. Pers. Comm. E-mail RE: White-tailed deer.

Ref 7. Boonstra R. and C.J. Krebs. 2006. Population limitation of the northern red-backed vole in the boreal forests of northern Canada. Journal of Animal Ecology 75:1269-1284

Ref 8. Boonstra R., C.J. Krebs and N.C. Stenseth. 1998. Population cycles in small mammals: the problem of explaining the low phase. Ecology. 79:1479-1488

Ref 9. Bowman J, R.D. Phoenix, A. Sugar, F. Neil Dawson, and G. Holborn. 2008. Spatial and temporal dynamics of small mammals at a regional scale in Canadian boreal forest. Journal of Mammalogy 89:381-387

Ref 10. Boyce M.S. and R.S. Miller. 1985. Ten-year periodicity in whooping crane census. Auk 102(3): 658.

Ref 11. Cabe P.R., in The Birds of North America Online, Ed. (A.Poole, Ed. (Cornell Lab of Ornithology. Ithaca, 1993).

Ref 12. Canadian Wildlife Service Waterfowl Committee. 2008. Population Status of Migratory Game Birds in Canada (and Regulation Proposals for Overabundant Species). November 2008. Canadian Wildlife Service, Environment Canada, Ottawa, Canada.

Ref 13. Krebs, C.J. 1996. Population Cycles Revisited. Journal of Mammalogy 77:8-24

Ref 14. Krebs, C.J. 2001. What Drives the 10-year Cycle of Snowshoe Hares? BioScience 51:25-35

Ref 15. Communities of Aklavik, Inuvik, Holman Island, Paulatuk and Tuktoyaktuk, S. Nickels, M. Buell, C. Furgal, and H. Moquin. 2005. Unikkaaqatigiit -- Putting the Human Face on Climate Change: Perspectives from the Inuvialuit Settlement Region. Joint publication of Inuit Tapiriit Kanatami, Nasivvik Centre for Inuit Health and Changing Environments at Universities. Laval and the Ajunnginiq Centre at the National Aboriginal Health Organization. Ottawa.

Ref 16. COSEWIC. 2006. COSEWIC Assessment and Status Report on the Rusty Blackbird Euphagus carolinus in Canada. Ottawa, ON.

Ref 17. COSEWIC. 2007. COSEWIC report on the status of Olive-sided flycatcher Contopus cooperi in Canada. Ottawa, ON.

Ref 18. COSEWIC. 2007. COSEWIC Status Report on the Common Nighthawk Chordeiles minor in Canada. Ottawa, ON.

Ref 19. COSEWIC. 2008. COSEWIC report on Canada Warbler Wilsonia canadensis in Canada. Ottawa, ON.

Ref 20. COSEWIC. 2008. Update COSEWIC Status Report on Short-eared Owl Asio flammeus in Canada. Ottawa, ON.

Ref 21. COSEWIC. 2009. COSEWIC Assessment and Status Report on the Red Knot Calidris canutus in Canada. Ottawa, ON.

Ref 22. COSEWIC. 2009. UNSOLICITED COSEWIC Status Report on the Horned Grebe Podiceps auritus in Canada. Ottawa, ON.

Ref 23. COSEWIC. 2009. Update COSEWIC report on the status of Eskimo Curlew Numenius borealis in Canada. Ottawa, ON.

Ref 24. COSEWIC. 2011. COSEWIC report on the Barn swallow Chirundo rustica in Canada. Ottawa, ON.

Ref 25. Crossman E.J. 1991. Introduced freshwater fishes: a review of the North American perspective with emphasis on Canada Can. J. Fish. Aquat. Sci. 48 (Suppl. 1):46-57

Ref 26. DeIgiudice G.D., R.O. Peterson, and W.M. Samuel. 2007. Trends of Winter Nutritional Restriction, Ticks, and Numbers of Moose on Isle Royale. Journal of Wildlife Management 61:895-903

Ref 27. Department of Environment and Natural Resources. 2006. Caribou Forever -- Our Heritage, Our Responsibility. A Barren-ground Caribou Management Strategy for the Northwest Territories 2006 - 2010.

Ref 28. Dickson D.G.H. 2002. Status of marine birds of the southeastern Beaufort Sea. Arctic 55:46-58

Ref 29. Doupe J.P., J.H. England, M. Furze, and D. Paetkau. 2007. Most northerly observation of a grizzly bear (Ursus arctos) in Canada: photographic and DNA evidence from Melville Island, Northwest Territories. Arctic 60:271-276

Ref 30. ENR Webpage. 2008. Dalls's sheep - Wildlife Webpage. Available at www.enr.gov.ca

Ref 31. Environment and Natural Resources. 2011. A Barren-ground Caribou Management Strategy for the Northwest Territories 2011-2015.

Ref 32. Environment and Natural Resources. 2006. Caribou Forever - Our Heritage, Our Responsibility.  A Barren-ground Caribou Management Strategy for the Northwest Territories 2006-2010. Yellowknife, NT.

Ref 33. Federal, Provincial, Territorial, Governments. 2010. Canadian biodiversity: ecosystem status and trends 2010 , Canadian Councils of Resources Ministers, Ottawa.

Ref 34. Finerty J.P. 1980. The population ecology of cycles in small mammals. Yale University Press, New Haven, CT, 234 p.

Ref 35. Fisheries and Oceans Canada. 2001. Rat River Dolly Varden . DFO Science Stock Status Report D5-61. Available at www.dfo-mpo.gc.ca/csas/Csas/status/2001/SSR2001_D5-61e.pdf

Ref 36. Gau R., R. Mulders, T. Lamb, and L. Gunn. 2001. Cougars (Puma concolor) in the Northwest Territories and Wood Buffalo National Park. Arctic 54:185-187

Ref 37. Harwood L.A. 2001. Status of anadromous Dolly Varden (Salvelinus malma) of the Rat River, Northwest Territories, as assessed through community-based sampling of the subsistence fishery, August-September 1989-2000. Canadian Science Advisory Secretariat (CSAS) Research Document 2001/090. Available at http://www.dfo-mpo.gc.ca/csas/Csas/DocREC/2001/RES2001

Ref 38. Hik D.S., J. Carey, and J. Carey. 2000. Cohort variation in horn growth of Dall sheep rams in the southwest Yukon, 1969-1999.

Ref 39. Ims R.A., J.A. Henden, and S.T. Killengreen. 2008. Collapsing population cycles. Trends in Ecology & Evolution 23:79-86

Ref 40. Jenkins E.J., A.M. Veitch, S.J. Kutz, E.P. Hoberg, and L. Polley. 2006. Climate change and the epidemiology of protostrongylid nematodes in northern ecosystems: Parelaphostrongylus odocoilei and Protostrongylus stilesi in Dall's sheep (Ovis d. dalii). Parasitology 132:387-401

Ref 41. Johnston R.F. 1992. Rock Pigeon (Columba livia) in The Birds of North America Online, A.Poole, Ed. Cornell Lab of Ornithology, Ithaca.

Ref 42. Krebs C.J. 1996. Population cycles revisited. J. Mammal.8

Ref 43. Krebs C.J. et al. 2002. Synchrony in lemming populations in the Canadian Arctic. Can. J. Zool. 80:1323-1333

Ref 44. Krebs,C.J., S. Boutin, and R. Boonstra. 2001. Ecosystem Dynamics of the Boreal Forest - The Kluane Project. Oxford University Press. 511 p.

Ref 45. Kutz S. et al. 2009. The Arctic as a model for anticipating, preventing, and mitigating climate change impacts on host-parasite interactions. Veterinary Parasitology 163:217-228.

Ref 46. Larter N.C., and D.G. AllaireD. G.2005. Sheep surveys of the Liard Range, Nahanni Range and Ram Plateau in the Mackenzie Mountains, August 2003. GWNT, ENR.

Ref 47. Larter N. C. and D.G. Allaire. 2007. Mackenzie Mountain Non-resident and Non-resident Alien Hunter Harvest Summary 2006.

Ref 48. Leary R.F. and F.W. Allendorf.1989. Fluctuating asymmetry as an indicator of stress: Implications for conservation biology. Trends in Ecology and Evolution 4: 214-217

Ref 49. Lowther P.E. and C.L.Cink. 2006. House Sparrow (Passer domesticus) in The Birds of North America Online. A.Poole, Ed. Cornell Lab of Ornithology. Ithaca.

Ref 50. Mochnacz N.J., J.D. Reist, P. Cott, G. Low and R. Wastle. 2004. Biological and habitat data for Bull Trout (Salvelinus confluentus) and associated species from stream surveys conducted in the southern and central Mackenzie River Valley, Northwest Territories, 2000 to 2001. Canadian Data Report of Fisheries and Aquatic Sciences 1131.

Ref 51. Mochnacz N.J., J.D. Reist, G. Low, R. Bajno and J.A. Babaluk. 2010. Sympatric Bull Trout (Salvelinus confluentus) and Dolly Varden (Salvelinus malma) in the Mackenzie Mountains, Northwest Territories, with updated notes on distribution and biology of both species. Arctic (in prep.).

Ref 52. National Audubon Society. 2008. Christmas Bird Count. Available at http://www.audubon.org/bird/cbc/ 

Updated: 20 December 2012

Wildlife health

15.7 Trends in winter tick in moose

This indicator tracks winter tick, a parasite that can have negative effects on moose.

The most obvious signs of winter tick are hair loss and poor, thin body condition. Affected moose are sometimes called “ghost moose” because of hair loss that results in white or grey patches. Winter tick is common on moose in southern Canada, but its range is thought to be limited by climate. It is not yet common in the NWT, but recent sightings of affected animals have led biologists to keep track of observations to see if this disease becomes more common in the NWT in the future. This indicator provides baseline information on the location of known observations of moose showing signs of winter tick.

Surveillance for winter tick in the NWT, like other wildlife diseases, relies heavily on reports from hunters and trappers who spend time on the land. Hunters across the NWT are encouraged to report any diseases or abnormalities seen in wildlife.

NWT Focus

Some diseases and parasites are limited by climate or long periods of cold weather. Climate change may impact where these parasites can survive, or allow them to move through their various life stages more quickly. Environmental changes may have occurred, or could occur in the future, that allow the winter tick to extend its range northwards. Changes in habitat that may increase contact between individual moose may also facilitate the spread of winter tick. Monitoring winter tick on moose is important because it can provide information on changes in climate or habitat that impact the health of moose populations, an important food and cultural resource to many NWT residents.

Current view: status and trend

Historical

Traditional knowledge in the NWT suggests that moose affected by winter tick were not observed until the last several decades.

In 1987 a survey was conducted of 502 trappers representing 389 registered trap lines in northern Alberta, northern BC, NWT and the Yukon. In this survey the northern limit of winter tick-related observations in the Yukon was 62 degrees north (see Figure)¹⁶. The only NWT reports were anecdotal reports of moose affected by winter tick recorded from Fort Providence in 1987 and near Fort Liard and near Fort Smith prior to 19671⁶. However, trappers north of 62 degrees in the NWT were not surveyed in this study.

Map: Locations of trap lines where moose were [solid circle] or were not [open circle] observed in late winter/early spring with apparent tick-induced hair loss, according to a survey of 502 trappers in 1987¹⁶. Source: Samuel 1989. Journal of Wildlife Diseases¹⁶.

Recent Observations

Overall, incidences of winter ticks in the NWT still appear to be very low and mostly confined to southern NWT, though sightings along the Mackenzie Valley as far north as the Sahtu region have been increasing.

Map: Observations of moose showing signs of winter tick in the NWT and reported to GNWT-ENR.

Looking forward

Changing environmental conditions may allow the winter tick’s range to extend northwards. Some experts think that the effects of winter ticks on moose across geographical regions are primarily weather-dependent⁴. In other parts of North America, tick-related mortality of moose sometimes occurs in many different regions in the same years, suggesting that something common is occurring in all locations. Spring has been suggested as the critical time period, when adult females drop off their host and must survive to lay eggs. Low precipitation and warm temperatures during April have been associated with increased number of ticks the following year, indicating this weather may support maximum survival and reproduction rates of the winter tick. April snow cover and low temperatures (less than 3-4 degrees C) have been linked to low tick survival.

Looking around

Moose and other hoofed animals throughout southern Canada are infested by the winter tick. The Yukon faced a recent tick infestation in its elk herds, causing concern for its moose population. To date, winter ticks in Yukon appear to be confined, for the most part, to two elk herds in the southwest. Yukon biologists plan to expand their surveillance efforts to get a better idea of the geographic and host species distribution of winter ticks in the Yukon.

Find out more

• More information on Winter Tick can be found on the Canadian Cooperative Wildlife Health Centre web site at http://www.ccwhc.ca/wildlife_health_topics/winter_tick/wintertick.php

Other Focal Points

Wildlife indicators are also linked to other focal points in this report. Healthy wildlife populations support strong cultures in DEMOGRAPHY - HUMANS IN THE NWT and provide goods and services to people in USE OF RENEWABLE RESOURCES. Pressures on wildlife are tracked in HUMAN ACTIVITIES and LANDSCAPE CHANGES. Protected wildlife habitat areas are part of PROTECTED AREAS AND LAND USE PLANNING. SPECIES AT RISK have their own chapter.

Updated: 20 December 2012

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Birds

15.8 Trends in bird population

This indicator tracks population changes for NWT bird species covered by the surveys noted below.

The two major biomes of the NWT, the tundra and the taiga-boreal forest, harbour 283 species of birds. The vast majority migrate outside the NWT in winter; only about 6% of bird species remain in the NWT year-round.

The information for this indicator is obtained, with permission, from the report "The State of Canada's Birds, 2012"¹² where trend analyses for each of Canada's large physiographic region and for different groups of birds are presented. This updated information replaces the data used previously in 2011 for this indicator.

Overall trends in all regions in Canada, by bird group.

"Aerial insectivores -- birds that catch insects in flight -- are declining more steeply than any other groups of birds."

"... shorebird species have declined by almost 50%"

Increasing waterfowl populations reflect successful management of hunting and wetlands.

Increasing raptor populations point to the success of direct intervention.
Quotes from "The State of Canada's Birds, 2012"¹²

Not all migratory species are declining, but many species are and there is growing concern that that is indicative of some widespread changes in our ecosystems. For example, there is evidence that most shorebirds nesting in the Arctic are declining¹³, some shorebirds in the taiga/boreal forest are also declining¹⁴, and many boreal bird species that specialize in aerial feeding on insects are also declining^{1, 2}. Further studies are needed to determine the main reasons for these losses in population numbers.

Some species have increased in numbers in the past few decades. For example, the number of lesser snow geese nesting in the western Canadian Arctic (mostly on Banks Island)³ has more than doubled since the 1970s probably due to increased availability of winter food as a result of changes in agricultural practices³. The peregrine falcon also has increased in numbers after contaminant levels were reduced, increasing their nesting success. See SPECIES AT RISK focal point.

Looking forward

A collaborative approach is essential to understand why some migratory birds are declining across North America, so that threats can be reduced and populations can recover from their long-term declines. Management and conservation strategies, such as the North American Bird Conservation Initiative, are being implemented by agencies responsible for the management of birds in the NWT, Canada, as well as in the US and Mexico.

Find Out More

Go to The State of Canada's Birds 2012 to find more information for other regions, more trends, and some solutions to improve the state of Canada's birds at www.stateofcanadasbirds.org/index.jsp

Go to the North American Bird Conservation Initiative to find more on collaboration in monitoring birds at www.nabci.net

Go to Bird Studies Canada for more information on the BBS and the CBC survey and the North American Bird Conservation Initiative at www.birdscanada.org

eBird enumberates bird checklist records from the NWT (formerly done under the NWT/NU Bird Checklist Survey). http://eBird.ca

Fore more information on Environment Canada's bird monitoring programs, go to http://www.ec.gc.ca/nature/default.asp?lang=En&n=4B88450F-1

Shorebird Conservation Strategy and Action Plan: http://www.ec.gc.ca/Publications/default.asp?lang=En&xml=44168E71-DC2E-4D12-8333-B3C83A23486F

For more information about US Fish and WIldlife Service's migratory bird program: www.fws.gov/migratorybirds/dmbmdbhc.html

For more information on bird trends in the United States go to the State of Birds Report 2011 at: http://www.stateofthebirds.org

Other focal points

See NATURAL CLIMATE FLUCTUATIONS and CLIMATE AND WEATHER for indicators on weather-climate events that may drive or influence population cycles in northern species.

Technical Notes

The Breeding Bird Survey (BBS) tracks species on their breeding grounds. There are only 5 survey sites in the NWT. The NWT/Nunavut Bird Checklist is tracking sightings of birds to help increase our knowledge of the distribution, abundance and breeding status of birds in NWT’s ecosystems. Some NWT birds migrating further south to the US, Mexico and central-south America, are monitored by the Canadian Migration Monitoring Network at a few stations in Canada, the US, and elsewhere.

The Christmas Bird Count (CBC), a monitoring program over 100 years old, collects data on birds at their wintering sites across North America. So far there are only 6 sites in the NWT and trends in ptarmigans, ravens and other species that stay in the NWT for winter can be tracked using this volunteer program. As most NWT birds migrate south for winter, the population trends of these species are determined from data collected at CBC sites in southern Canada and the United States. The BBS and CBC programs are administered in Canada by Birds Studies Canada and provide the majority of data to determine population trends on most small birds nesting in the NWT. To learn more on how these programs are used to help bird monitoring in the NWT, consult the Northern Landbird Program Strategy and Action Plan (2002).

Ducks and geese are monitored on their breeding grounds using annual aerial and photo surveys performed by the US Fish and Wildlife Service. They use the data to track the status of waterfowl and help review hunting regulations every season. Waterfowl surveys are part of the North American Waterfowl Management Plan.

Some monitoring programs have been designed to collect data on some species of birds requiring special attention in the NWT and elsewhere. The status NWT shorebirds are tracked by the Program for Regional and International Shorebird Monitoring (PRISM) as part the Shorebird Conservation Strategy and Action Plan (2006). Monitoring of raptor nesting sites in the NWT is done using the NWT-NU Raptor Database. Peregrine Falcons are monitored every 5 years in two study areas in the NWT as part of the North American Peregrine Falcon Surveys.

Raw data from the CBC can be downloaded from http://www.audubon.org/bird/cbc/index.html.

The previous information used for this indicator in 2011 has been archived and is available upon request at NWTSOER@gov.nt.ca

Updated: 20 December 2012

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Fish

15.9 Status of Dolly Varden and Bull Trout

This indicator tracks the status of river chars, Dolly Varden (Salvelinus malma) and Bull Trout (S. confluentus) using changes in abundance and population structure such as length and age.  Hybridization is also monitored as the occurrence of hybrids might signal significant environmental change. These two species differ from the Arctic Char (Salvelinus alpinus) mostly found east of the Mackenzie Delta, but they mostly are called char by local users in all the NWT.

Dolly Varden, Salvelinus malma © P Vescei                               Bull Trout, Salvelinus confluentus © P Vescei                                                                                                                       

Information and analysis for this indicator were provided by C.D. Sawatzky, N.J. Mochnacz, and J.D. Reist, Fisheries and Oceans Canada, Winnipeg, based on studies done for the International Polar Year - Climate Change Effects on Char in the Arctic Project.

NWT Focus

Char species, such as Dolly Varden and Bull Trout, can be used to monitor changes in both the Arctic Ocean and freshwater ecosystems.  Dolly Varden and Bull Trout are particularly good fish species to monitor because they have life history stages that occupy different habitats during their lifetime, for example sea-run fish link lakes, rivers, estuaries and near shore habitats.  Each species’ life stage is exposed to the same environmental stressors, but may respond differently to these stressors, thus increasing our understanding of cumulative effects. Possible responses of char to environmental change include:
i) loss of local biodiversity (e.g., hybridization/introgression would lead to a loss of genetic integrity);
ii) shift in biodiversity (e.g., sea-run fish may switch to freshwater only if local production increases);
iii) shifts in fish population parameters (e.g., growth rate, age-at-maturity, life history, reproductive frequency shift);
iv) loss of local populations due to a) habitat change exceeding thresholds, or b) impact of colonizing species via competition, predation, parasitism or disease.

Current status and trend

a. Distribution

Dolly Varden 

Dolly Varden are present as anadromous (i.e., sea-run) fish in coastal waters of the Beaufort Sea in the western Arctic primarily west of the Mackenzie Delta during ice-off periods (i.e., summer and early autumn). Offshore distribution is poorly known mostly due to poor sampling efforts; however, our present understanding suggests that adults and juveniles mainly occur in nearshore waters in marine areas within the 0-10 m isobaths. Dolly Varden use habitat in freshwater streams for spawning, overwintering, rearing, feeding and resting. This species is primarily adapted to flowing waters, thus is often found in high-gradient rivers associated with perennial groundwater springs. These groundwater sources are essential for northern populations because they maintain winter habitat and provide high-quality spawning habitat. However, these areas are limiting in most streams. In the Northwest Territories, anadromous Dolly Varden occupies drainages of the Big Fish, Rat and Vittrekwa rivers. The furthest known upstream location (and currently the only known site upstream of Point Separation in the Mackenzie Delta) where this species is found in the Mackenzie River basin is in the Gayna River^{10, 15}.

Gayna River, NWT Credit: DFO/N Mochnacz

Bull Trout

Bull Trout from interior North America (i.e., Idaho north to the Northwest Territories) only use freshwater environments to carry out their life cycle. They are distributed in the western portion of the Northwest Territories in Mackenzie River drainages north to the central Sahtu Settlement Area. To date, the northernmost record of Bull Trout is in the Gayna River. This is the only location where Bull Trout and northern Dolly Varden are known to be sympatric. Additional sampling in suitable habitats surrounding this area is required to confirm and extend this understanding^{10, 15}. This species utilizes similar habitats to those of Dolly Varden in high-gradient freshwater streams, however, populations are also found in larger slow-flowing rivers such as the Mackenzie mainstem, and occasionally in lakes in the NWT.

b. Hybridization/Introgression

There is presently no evidence (genetic or morphological) for hybridization of Bull Trout and Dolly Varden in the Northwest Territories, which suggests that if this event occurs it is very infrequent¹⁰. Accordingly, the genetic integrity of the two species is intact in this area and occurrence of hybrids might signal significant environmental change.

c. Fluctuating Asymmetry

Fluctuating asymmetry (FA) in paired structures (e.g., different counts for left- and right-side fin rays) has been noted as a potential, but somewhat controversial, indicator of environmental and genetic stress in fish populations⁸. FA may occur when development is disrupted as a result of either environmental change, genetic stress, or a combination of both. The frequency of occurrence of this event is currently being investigated in northern Canadian populations of Dolly Varden and Bull Trout. Both low asymmetry and stable temporal patterns of symmetry/asymmetry suggest minimal environmental stress on the fish.

d. Abundance

Dolly Varden

The Rat River (67.62°N, 134.87°W) is the only population that has been periodically studied for population size over the past 10 years.  Mark-recapture population estimates exist for between 1989 and 1998⁶. Population estimates up to 2007 are forthcoming.

Rat River (Fish Creek), NWT Credit: DFO/N Mochnacz

The Dolly Varden in the Rat River is the only population that has been periodically studied for population size over the past 10 years.  In 1998, the population numbered about 15,000.  Prior to 1999, there was evidence from the fisheries data at Rat River of loss of larger/older fish, suggesting population-level effects.  Recovery in later years (e.g., 1999 and 2000) was thought to be related to higher growth rates due to above average productivity in 1998 and/or the effect of decreased fishing pressure.

Mark-recapture population estimates (with 95% confidence limits) for the Rat River Dolly Varden population Source: DFO⁶.

Bull Trout

Preliminary work suggests that most populations are relatively small, widespread, and perhaps fragmented¹⁰.

Density and growth estimates for juvenile Bull Trout in Funeral Creek (~ 61.60°N, 124.82°W) have been calculated. The estimated average annual growth of juveniles captured (age 0 – 5 years) was 27.9 mm/yr in length and 14.2 g/yr in weight; however, after age five the average annual weight gain increased to approximately 60 g/yr. The density of juveniles captured in two different reaches from Funeral Creek during September 2001 was 5.6 and 6.7 fish//100 m², respectively⁹. This would be a suitable location for future monitoring.

e. Population Structure (Length & Age)

Dolly Varden

Length-frequency distribution of current year non-spawning Rat River Dolly Varden caught in subsistence fisheries at Destruction City (on the Rat River) from 1986-1994, and at five monitoring sites (including Destruction City) from 1995-2000.Source: DFO⁷.

Age-frequency distribution of Rat River Dolly Varden caught in the subsistence fisheries at Destruction City from 1986-1994, and at five monitoring sites (including Destruction City) from 1995-2000⁷.

Truncation in size and/or age structure, particularly loss of larger/older fish (e.g., 1997) suggests population-level effects. Recovery in later years (e.g., 1999 and 2000) suggests relaxation of perturbing factors.

Bull Trout

Although sample sizes are low, data suggest that non-migratory (i.e., stream-resident), and migratory (adfluvial, and fluvial) populations occur in the area1. Non-migratory fish are smaller once sexually mature and grow slower than migratory fish.

Length-at-age plot of non-migratory and migratory Bull Trout from the Northwest Territories. Points to the right of the straight and dashed lines represent mature non-migratory and migratory fish respectively.

Looking Around

The southern taxon of Dolly Varden (S. malma lordi) is secure throughout its range (southern Alaska, British Columbia to Washington), and the northern taxon (S. malma malma) is secure throughout Alaska, however, it appears to be stressed in north-western Arctic Canada (COSEWIC assessment is currently underway; two of five anadromous populations appear to be stressed).

According to NatureServe¹¹ rankings within the continental USA, five of five distinct populations of Bull Trout (ranked as vulnerable as a species) rank as critically imperiled (n = 1) or imperiled (n = 4). The status of Bull Trout populations in the Northwest Territories is poorly understood, although most populations appear to be small and have specific habitat requirements (e.g., perennial groundwater springs) associated with higher order stream reaches. COSEWIC plans to assess this species in Canada in the next 1-2 years.  

Virtually all stressors which are known to affect fish populations generally have been documented as affecting chars, a group which appears to be particularly susceptible to both local (e.g., exploitation) and pervasive (e.g., climate change) stressors as well as individual and cumulative effects of stressors. Additional stressors include habitat degradation, industrial development, and fragmentation of watercourses and species introductions. Southern populations (south of 60°N) of chars appear to be at greater risk overall as evidenced by higher levels of conservation concern. Two conclusions thus result: i) southern populations of chars, particularly those isolated in lakes or requiring unperturbed river habitats are at acute risk, and given their probable evolutionary history represent an irreplaceable component of biodiversity of the char group; and ii) southern populations are useful proxies of potential future effects and issues facing northern chars. Accordingly, appropriate care in addressing conservation, management and stressors of both chars and their ecosystems is required, particularly as wide-reaching changes occur throughout the north¹⁷.

Looking forward

Possible responses of char to environmental change include:

i) loss of local biodiversity (e.g., hybridization/introgression would lead to a loss of genetic integrity);
ii) shift in biodiversity (e.g., sea-run fish may switch to freshwater only if local production increases);
iii) shifts in fish population parameters (e.g., growth rate, age-at-maturity, life history, reproductive frequency shift); and
iv) loss of local populations due to a) habitat change exceeding thresholds, or b) impact of colonizing species via competition, predation, parasitism or disease.

Find Out More

Sawatzky, C.D. and Reist, J.D. 2009. The state of char in the Arctic [in Arctic Report Card 2009].  Available from: http://www.arctic.noaa.gov/reportcard [accessed 10 November 2009].

Other focal points

See WATER for indicators on water quality and quantity. 

Technical notes

Methods for determining the distributions of these species are outlined in Sawatzky et al. (2007)¹⁸ and Mochnacz et al. (in prep.)¹⁰.

Rat River population estimates (Petersen method) were based on tagging Dolly Varden that were collected by seining at the overwintering area and recapturing fish the following year through the subsistence fishery, with the exception of 1989 when electro-shocking was used to recapture the fish⁶.

Funeral Creek abundance estimates were based on the Zippin three-removal method¹⁹. Three consecutive electrofishing passes were performed in an upstream manner and the number of Bull Trout captured during each pass was recorded. The maximum-likelihood population size was calculated based on the number of fish captured on each electrofishing pass¹⁹.

Updated: 29 July 2011

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Reference List

Ref 1. Bird Studies Canada. BirdLife International. 2008. Common insect-eating birds suffer dramatic declines. Bird Studies Canada. Available online at http://www.birdlife.org/news/news/2008/03/Canada_insectivore_decline.html

Ref 2. Blancher P. 2003. The importance of Canada's boreal forest to landbirds. Canadian Boreal Initiative and the Boreal songbird initiative.

Ref 3. Canadian Wildlife Service Waterfowl Committee. 2008. Population Status of Migratory Game Birds in Canada (and Regulation Proposals for Overabundant Species). November 2008. Canadian Wildlife Service, Environment Canada, Ottawa, Canada.

Ref 4. DeIgiudice G. D., Peterson R. O., Samuel W. M. 2007. Trends of Winter Nutritional Restriction, Ticks, and Numbers of Moose on Isle Royale. The Journal of Wildlife Management 61:895-903

Ref 5. Federal, Provincial, Territorial, Governments. 2010. Canadian biodiversity: ecosystem status and trends 2010. Canadian Councils of Resources Ministers, Ottawa

Ref 6. Fisheries and Oceans Canada. 2001. Rat River Dolly Varden.

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