Dall's Sheep in the NWT

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Dall's sheep (Ovis dalli dalli) are one of the most spectacular animals found in alpine regions. To the Dogrib they are known as Sahzhoa, in North Slavey they are referred to as Doge, and the Gwich'in know them as Divii. Posing regally in their white coats against the green and grey summer alpine habitat, they are a delight to photographers as their large curled horns complete an impressive picture. 

Mountain sheep in North America are classified as either bighorn sheep (Ovis canadensis) which occur mainly in the Rocky Mountains or thinhorn sheep (Ovis dalli) which occur farther north. Among thinhorn sheep there are two subspecies - Dall's sheep (Ovis dalli dalli) and Stone's sheep (Ovis dalli stonei). Dall's sheep are found in Alaska, the Yukon, the western NWT and extreme north-western British Columbia. They are pure white with amber-coloured horns. Stone's sheep are found in the southern Yukon and northern British Columbia. They are silver grey to black with white patches on the rump, forehead, muzzle, and hind legs. Grey sheep have been seen occasionally in the NWT near the Yukon border and these may be intergrades between Dall's sheep and Stone's sheep.

Dall's sheep are medium-sized, hoofed mammals (ungulates). Rams weigh from 80 to 100 kg and ewes are smaller at 60 kg. Both rams and ewes grow horns throughout their lives. The horns of the ewe are less curved, more slender and shorter (about 25 cm in length) than the ram's.

In the Mackenzie Mountains of the NWT, an average ram has horns of 85 to 90 cm around the outer circumference and 33 cm around the bases. By age 5, a ram usually has horns of three-quarters curl (270°). Full curl is reached by 7 or 8 years of age. The greatest horn length from a Dall's sheep ram ever recorded had an outer circumference of 125.7 cm. The horns of a ram stop growing each fall, resulting in a grooved rest line. Like tree rings, these lines can be used to determine the age of the ram. Most sheep live for 8 or 9 years, although they have been known to reach 14 to 16 years of age. Dall's sheep have a coat that is ideally suited to a cold, harsh climate. Long hollow guard hairs cover an undercoat of fine wool. In winter the coat is long, often growing to a length of more than 5 cm. It reaches its full length before December and gives the sheep a stout appearance. In spring the long hair is shed, giving way to a short summer coat. By August, their coat is stained by soil in a variety of pastel shades. Newborn lambs occasionally have a large amount of brown in their coats but this is lost or overgrown within 2 weeks of birth. Dall's sheep are graceful and agile in their rugged, mountainous habitat. The pliable centre of their hooves is surrounded by a hard rim, providing good traction on steep, rocky outcrops. Sheep have excellent eyesight, and a well developed sense of smell, both of which allow them to detect danger from a considerable distance.

Distribution

Dall's sheep are found in the Mackenzie Mountains west of the Mackenzie River, and in the Richardson Mountains. In the Richardson Mountains they are located primarily on Mount Goodenough, locally referred to as Black Mountain. Mount Goodenough is approximately 50 km southwest of the community of Aklavik.

Grey shaded area - Distribution of Dall's Sheep

In the Richardson and Mackenzie mountains, snow may accumulate in some places and be almost completely swept off by winds in other places, such as low plateaus and ridges. It is these latter areas that are important as Dall's sheep winter range from October to May, especially if they are adjacent to precipitous escape terrain. The total size of the winter range used by Dall's sheep is usually much smaller than the summer range. In early summer, as the snow melts, sheep merely expand their movements to incorporate recently exposed, greening vegetation, generally at higher elevations. They feed heavily during this time to build-up the fat reserves that must last them through the winter.

Individual Dall's sheep confine almost all their movements to a particular mountain block, or range, that contains both the winter and summer range. For example, in the Mackenzie Mountains, 100 to 200 sheep may be found on a particular mountain block and they use the same winter and summer ranges each year and from generation to generation. This loyalty to seasonal ranges and one mountain block means that Dall's sheep are very slow to re-colonize an area if the population is severely reduced for some reason. It also means that the sheep are very sensitive to intense human activity on their ranges. They are reluctant to move from their terrain when roads, mines, and camps appear suddenly on the scene.

Behaviour

Usually, rams that are older than 4 years and ewes remain in separate groups. These older rams often roam in small groups of 3 to 10 individuals, but sometimes rams are found alone. Ewe groups tend to be larger and contain young rams, yearlings, and lambs of the year.

Within a ram group a hierarchy exists. The oldest, largest horned individuals are dominant over younger, smaller horned individuals. These dominance relationships are maintained by regular social interactions between rams involving specific behaviour patterns such as shrub horning, horn displays, foreleg kicks, mounting, body horning, rubbing, nuzzling, and threat jumping, with occasional butting and clashing. The dominant ram usually leads a ram group.  A hierarchy also exists in each ewe group with young rams being dominant. In ewe groups, however, it is usually the oldest ewe that leads the group. Social interactions in ewe groups are less frequent that in ram groups, although the same behaviour patterns, such as horn displays and butting, are seen.

Dall's sheep are particularly sensitive to noise, and the sound of aircraft and vehicles can cause them to scatter and flee in panic. Although developmental activity in the Mackenzie Mountains has been minimal so far, future exploration, mines, roads and camps could pose new hazards to Dall's sheep. This may result in the separation of lambs from their mothers, over-exertion or injury causing death or withdrawal from critical range.

Reproduction

As the breeding season approaches in October and early November, rams begin to associate regularly with ewes. As associations increase, so do confrontations among the rams, usually resulting in head butting and clashing. In a clash, two rams several metres apart rise up on their hind legs and slam forward and downward into each other. Although their thickened skulls are an adaptation to the tremendous impact of these clashes, bloodied faces and splintered, or broomed, horn tips are not uncommon. Such contests are usually won by the largest rams who have the advantage when the ewes are in estrus and ready for breeding. Once the ewes are in estrus, interactions between the rams become less ritualized and consist mainly of blows delivered to the sides of opponents and dominant rams chasing subordinates away from estrus ewes.

A dominant ram will guard an estrus ewe for 2 to 3 days until she indicates her willingness to mate. Since they are polygamous, after breeding, the ram will seek out additional estrus ewes. 

Although Dall's sheep often become sexually mature as yearlings, most rams will not breed regularly until they are about 5 years old. However, ewes in vigorous, increasing populations may breed as early as 1 1/2 years of age, or during their second fall.  In the Mackenzie Mountains, the rut extends from mid-November to mid-December followed by a gestation period of about 175 days. Most mature ewes are impregnated during the rut. However, conditions during the winter and the availability of quality forage are important in determining lambing success in the spring. Ewes entering winter in poor condition may not give birth. The lamb's first winter is critical and many do not survive. In the Mackenzie Mountains, about 75% of the ewes give birth annually, and 80% of the lambs survive their first few months. At the end of 12 months only about half of the lambs remain alive.

Newborn lambs weigh 2 to 4 kg at birth. They develop rapidly and are able to explore the rocky terrain within a few days after birth and in a week are nibbling vegetation. Although the mother/lamb bond persists into late fall, lambs show considerable independence within a few weeks of birth and in the summer can frequently be seen romping together in groups some distance from the ewes. Nursing continues for 6 to 7 months after birth but becomes less frequent through the summer and early fall. By December, weaning is usually complete. 

Diet

Grasses and sedges make up about 70% of the diet of Dall's sheep, although their diet probably varies geographically. The leaves and stems of some shrubs and certain flowering plants are also selected and may be important seasonally. Lichens and mosses may be eaten in winter when the sheep often must paw through several centimetres of snow. In the summer, Dall's sheep spend most of their time feeding, with major feeding periods occurring in the early morning and late afternoon. Feeding is interspersed with occasional breaks to rest and ruminate.

Predators

Dall's sheep in the NWT have a number of predators including wolves, black bears and grizzly bears, wolverine, lynx, coyotes, and golden eagles. The amount of predation on Dall's sheep in the Northwest Territories is unknown. The rugged terrain preferred by sheep, and their usual proximity to precipitous escape areas affords them considerable protection from most predators. Each year, however, some lambs and adults are taken by predators, especially by the more agile species, such as wolves.

Parasites

Dall’s sheep in the NWT are generally healthy, but they are hosts for a variety of parasites.

Dall’s sheep are infected by a variety of gastro-intestinal parasites, none of which can be transmitted to humans, including the roundworms Marshallagia spp., Nematodirus spp., Trichuris schumakovitschi, Skrjabinema ovis, and the protozoa Eimeria. These parasites don’t appear to cause death in sheep, however, heavy infections with the abomasal worm Marshallagia spp. are associated with poorer body condition and lower pregnancy rates in ewes.

Parelaphostrongylus odocoilei is a roundworm found in the muscles of almost 100% of Dall’s sheep in the Mackenzie Mountains, but not the Richardson Mountains. Eggs of P. odocoilei are deposited in the blood vessels and carried to the lungs. In the lungs they hatch to larvae and cause considerable inflammation. Death due to respiratory failure has occurred in at least one heavily infected yearling. The role of this parasite in the health of the population is under investigation. It is not transmittable to humans.

Protostrongylus stilesi, or sheep lungworm, is present in almost 100% of Dall’s sheep in the Mackenzie and Richardson Mountains. Lungworm has been linked to pneumonia outbreaks and die-offs of bighorn sheep in the south, but other disease agents (bacteria and sometimes viruses) and a stress trigger are considered more important in causing this complex disease. Pneumonia cases have been sporadically reported in Dall’s sheep of the Mackenzie Mountains, but no die-offs have been detected and populations are stable. 

Contagious ecthyma can be found in Dall's sheep in the NWT, and can occasionally infect other ungulates including caribou and muskox. This virus causes scabby lesions most commonly found on the lips, mouth and skin of the face, around the edge of the hooves, and on the udder, vulva or pizzle. If mouth lesions are severe enough, animals will not feed, and lameness may occur due to foot lesions. In both cases, animals will lose condition and in sever cases may even die of starvation. The disease is self limiting, and animals will generally recover completely. The orf virus can infect people, so care should be taken in handling obviously infected animals.

Management

The first extensive studies on Dall's sheep in the Mackenzie Mountains were conducted by the Canadian Wildlife Service in 1966 to 1974. In several separate study areas, their research showed that the population in the Mackenzie Mountains was stationary. More recent studies done by Wildlife and Fisheries in the same study areas suggested that this situation had not changed.

Although the overall harvest rate in relation to population size is relatively low, some areas near communities can be subject to heavy localized hunting. This is a management concern because Dall’s sheep tend to remain within the same mountain block from one generation to the next. This reluctance to move means that sheep are very slow to re-colonize areas where numbers have been reduced.

In the land claim settlement area of the Sahtu Dene and Metis, biologists with the GNWT and the region's wildlife management board have established four study areas to do long-term annual population monitoring of Dall's sheep. The research is done by hunters from three communities who have been trained in sheep research and data recording by biologists and conservation officers. Hunters were trained in 1997 and data collection began in June/July 1998.

The most important requirement for the future is habitat protection. Critical habitat such as winter range, lambing areas, and mineral licks needs to be identified and protected. With careful management, Dall's sheep in the Northwest Territories will thrive and continue to provide opportunities for hunting, recreation and study.

Harvest Levels

Dall's sheep in the Mackenzie Mountains are important as a trophy species. Trophy hunting of Dall's sheep by outfitted hunters began in the mid-1960s after many years of light subsistence hunting by local residents. At present, there is no quota on the total number of rams that can be taken by outfitted hunters in the Mackenzie Mountains, but the number of sheep harvested is limited by the vastness and inaccessibility of the area.

For resident and non-resident hunters, the Dall's sheep hunting season is July 15th to October 31st. These hunters are limited to one adult male Dall's sheep per hunting season, with a minimum 3/4 curl in the horns. Non-residents must hunt with a licenced outfitter.

The numbers in the following chart have been taken from the annual NWT Resident Hunter Survey performed by ENR. Non-resident harvest numbers have been collected from Regional ENR offices.

Year	Resident Harvest	Non-resident Harvest	Total
1991/1992	4	170	174
1992/1993	13	203	216
1993/1994	15	191	206
1994/1995	17	199	216
1995/1996	20	190	210
1996/1997	10	201	211
1997/1998	17	210	227
1998/1999	5	215	220
1999/2000	7	204	212
2000/2001	7	189	196
2001/2002	7	199	206
2002/2003	Not Available	173	173
2003/2004	Not Available	213	213

Total annual harvest of Dall’s sheep in the Mackenzie Mountains is 230-240 sheep, representing about 1 to 1.5% of the total estimated population. Current harvest levels are considered to be within sustainable limits.

Resident hunters do not need a outfitter to hunt Dall's sheep in the Mackenzie Mountains, yet the annual harvest is small. For resident hunters, one sheep has an estimated replacement value of $600.

Most Dall’s sheep in the Mackenzie Mountains are harvested by non-resident hunters. They must use the services of a licenced outfitter during their hunt. A guided Dall's sheep hunt in the Mackenzie Mountains can cost approximately $10,000 Canadian per hunter.

Hunting in the Richardson Mountains is restricted to General Hunting License holders and the annual harvest is very small. In the Mackenzie Mountains, General Hunting License holders harvest 20-30 sheep per year. A sheep yields approximately 32kg of meat giving this harvest an estimated replacement value of between $12,000 to $18,000 per year.

Population Status

Surveys to count Dall's sheep over the entire Mackenzie Mountain area have not been done. However, based on aerial and ground surveys of several mountain blocks, the population of Dall's sheep is estimated to be 15,000 to 26,000.

In the northern Richardson Mountains, a survey in 1991 resulted in a count of 1510 sheep.

Location	Years	Month	Survey Type	Total Area (km2)	Sheep count	Density per 100km2	Reference
Unit 4G	1966-73	Feb & July	Fixed-wing	236	110	47	Simmons et al. 1984
Unit 6H	1966-73	Feb & July	Fixed-wing	196	100	51	Simmons et al. 1984
South Nahanni	1984	June	Helicopter	1100		51	Ferguson et al. 1987
South Nahanni	1984-88	June	Helicopter	2900		30	Ferguson et al. 1987
Zone E1-1	1988	June	Helicopter	4956	934	19	Latour and Maclean 1994
Unit 4G	1990	June	Helicopter	236	58	25	Shank et al. 1993
Unit 6H	1990	June	Helicopter	196	84	43	Shank et al. 1993
Unit 6H	1991	June	Helicopter	196	80	41	Shank et al. 1993
Katherine Ck.	1998	April	Ground	402	197	49	A. Veitch. Unpub. Data
Palmer Lake	1998	Sept	Ground	319	312	53	R. Popko. Unpub. Data