It's a Swell place for Sheep
Rusty Robinson concludes two years of field study on big horn sheep
The desert bighorn sheep in northern Emery County have a wide area to roam. They travel between the Wedge area south to Eagle Canyon and points beyond. Rusty Robinson has been following these sheep in their wanderings for the past two years. He has been involved with a project to study the bighorn sheep and learn why their population has decreased over the past several years.
Robinson said, "The Division of Wildlife Resources wanted to do this study for a long time. The sheep population has been dwindling since 2001." Actual sheep population now is 130-150 animals. In 2001, there were 326 actual animals counted.
Robinson said, "The sheep have experienced a die-off due to bacterial respiratory diseases. There are a couple of strains of bacteria which they have likely contracted from association with domestic sheep or goats. Bighorn sheep have been spotted close to towns where the chance they mingle with domestic herds is greater. Domestic sheep and goats are also known to get loose and wander out where the big horn sheep live. This bacteria doesn't affect the cattle or horses and burros on the Swell.
The bighorn sheep originally crossed the Bering Strait from Siberia to North America, and they have no natural resistance to the diseases carried by European domestic sheep."
Mycoplasma ovipneumoniae is the strain known most for causing die-offs in bighorn sheep populations.
Robinson said there was a steady decline in the population from 2001-2012. Now the population is seemingly stable but could experience future pneumonia outbreaks if triggered by environmental stressors, which could include drought, poor quality diet, bad winters or other conditions. Lamb survival has been high for the last two years. Usually, if respiratory disease is present in the population, then the lambs die very quickly after birth, but that hasn't been the case the last two years.
The lamb crop for the past two years has been very plentiful with a very high percentage of age appropriate ewes giving birth. There is a ram:ewe ratio of 53:100 in the herd. The lamb:ewe ratio was 31:100 ewes last November. Typically yearling ewes do not have lambs.
If a bighorn sheep lives 10-12 years it's considered a long life. After that age their teeth get so worn down it's hard for them to eat. Desert bighorn sheep are good eaters. Their diet can consist of more than 100 types of vegetation. They like grasses, shrubs, and forbs; they aren't picky. The male sheep will generally congregate together except during the rut in November when they will fight over the females in the herd. The sheep will live in small family units usually two to 10 sheep together. Currently, one hunting tag is given for the Northern San Rafael hunting unit. Seven tags are given for the southern unit. Wade Paskett works for the DWR and is involved in the management for the bighorn sheep. He has been very supportive of the research project Robinson has been working on for two years now.
Research gathered by Robinson will be used to adapt and adjust the current management plan to meet the current status of the herd.
Usually the older the ram the larger the horns. Horn growth will depend a bit on heredity and the diet of the animal. Horns will grow a little larger each year than the previous year. The sheep do not lose their horns each year as some species, but maintain the one set of horns throughout their life.
The bighorn sheep is native to the northern San Rafael Swell. About 40 animals were reintroduced in the 1970s. This planting was part of the statewide management plan by the DWR. The sheep that came here were from the San Juan unit.
Sheep are very difficult to manage, they are a very sensitive species and prone to disease. Sheep cover a lot of ground and have a large home range.
Robinson said, "Sheep will live where they have a lot of escape terrain. They seek out the steep and rugged terrain to avoid predators. Natural predators to the sheep include mountain lions and coyotes who go after the lambs. Over the last two years of the study, cougar predation has been responsible for half the mortality of these sheep. The impact of the mountain lions will be noted in the study."
Part of the study has included the use of tracking collars on the sheep. Thirty ewes and eight rams were outfitted with collars. These collars record the information concerning sheep movement and location. The first year the collars were on, 10 of the sheep died and 10 more were outfitted and then 10 more died the following year. The testing of these dead animals is called a necropsy. Results from the testing of these dead sheep will be included with the study report. In the summers the sheep go down deep into the canyons to stay cool. Sheep don't need a constant water source and they are able to obtain water from the foods they eat.
They can live and wander quite a distance from water. The lambing season is just beginning for the sheep and lasts from around April 30 to June 15. Peak of lamb production is around May 20. During the lambing season the ewe will isolate herself from the herd to have her lamb.
She will generally stay away from the herd for two-three days after which she will rejoin the herd with her new lamb. The sheep are very social animals. The lambs will nurse throughout the summer and by the end of summer they will be eating solid foods as well as nursing.
The habitat on the Swell is great for desert bighorn sheep and the population right now is well below what the range could sustain (the carrying capacity). When the herd was larger in the early 2000s there wasn't a problem with habitat. The sheep were well dispersed throughout the area from the Reef to Eagle Canyon. Paskett said the management plan contains a numbers objective of 500 sheep, and right now the goal is to rebuild the herd to that number. Planting more sheep has been discussed but the respiratory disease complicates translocating new sheep into the area because any new sheep brought in could contract the disease.
The herd in Zions Park right now is disease free, but other herds in Utah do have the disease.
Robinson said, "This herd has stabilized for now. It's a chronic problem, but there has not been an acute die-off for at least a couple of years now. The population is stable. But, environmental stressors could lead to another die off."
Paskett said the sheep are very important to the sportsmen. Sheep hunting brings good revenue into the state. The DWR would like to keep the sheep healthy not only for the hunters but for those people who like to watch wildlife in their natural habitat.
Bighorn sheep are popular watchable animals and a valuable animal to hunt. The desert bighorn sheep hunt is a draw hunt once in a lifetime permit. Paskett said this study will help the DWR understand the issues with the species population and will enable them to make good management decisions. "There aren't a lot of older age class rams to harvest on the North San Rafael, but there is still some opportunity to hunt. We don't want the older animals to die of old age or disease without giving sportsmen the opportunity to harvest them. We also want them to be successful."
Bighorn sheep aren't big bodied animals.
In the fall of 2013, the actual numbers counted were 94 on the north and 188 in the south San Rafael. With the sightability percentage factored in, the estimate of population is 156 in the north and 289 in the south. The DWR figures they count 60-70 percent of the animals and adjust the figures to get an approximate head count.
In 1979 when the herd was planted there were 40 animals. In the ensuing years the population grew to a high of 500 in 2001. Since then the numbers have trended significantly downward to 156 animals to date. Lamb survival is trending upward and Paskett said, "We are cautiously hopeful the herd has stabilized. Based on our count, that's what we are observing."
The herds are counted during the rut when larger groups gather together.
Paskett said they encourage people with hunting dogs to get a cougar permit and try hunting cougar on the Swell. The hunting will be difficult and challenging, but would really benefit the sheep population.
Robinson said they are missing nine sheep collars. If you happen to come across a sheep collar while out hiking there is a $100 reward for its return to the DWR. These collars are important and contain valuable information concerning the geospatial data to create habitat models regarding the sheep's location and mobility.
Robinson said he has recently concluded his two years of field work on the project. Now he will return to BYU and spend the next two years compiling everything he has learned about the sheep into graphs, documents and case studies with conclusions about the status of the northern San Rafael herd.
"I will be in the data analysis portion of the study. I will study the geographical data from the GPS collars. The data will be included on habitat use maps." Robinson expects to write three or four manuscripts from his research and a population report. One report will contain survival trends and lamb mortality and cause of death. All factors will be noted that might keep the herd from growing.
The project is for Robinson's PhD in Wildlife and Wildlands Conservation. He is currently attending Brigham Young University. When he's finished with school he would like to teach at a university.
The current project is being funded by FNAWS-Foundation of North American Wild Sheep, the DWR, and BYU.
Robinson said those involved have been very supportive of the research project.
Robinson was also involved in a polar bear research project in Alaska. He studied polar bears for three winters.
Robinson said he's going to miss his travels to the Swell to observe the sheep, but now it's time to put what he's learned on paper for the benefit of the herd and look for ways to better manage the sheep so they can have a bright future on the Swell.