Muskox: An Iconic Arctic Species, Then and Now

By Hillary Robison, National Park Service

With their helmet-like, sharply upturned horns and stocky long-haired bodies, muskoxen (Ovibos moschatus) conjure up in one’s mind images of a prehistoric world. Muskoxen are an iconic species in northwest Alaska whose closest relatives are the gorals (Naemorhedus spp.) and serows (Capricornis spp.) of Asia (Yang et al. 2013). Once common in Alaska, muskoxen were heavily hunted and extirpated from Alaska by the mid- to late-1800s (Lent 1988, Allen 1912).

Conducting muskox population surveys in Cape Krusenstern National Monument.

NPS Photo / Hillary Robison

Muskox were reintroduced to Alaska in 1935; 34 animals were captured in eastern Greenland and translocated to Nunivak Island (Gunn and Forchhammer 2008, ADFG 2016). The population on Nunivak Island thrived and in 1970 and 1981, 36 and 35 muskoxen, respectively, were introduced into the Seward Peninsula from Nunivak Island. Additionally, between 1970 and 1977, 70 muskoxen were reintroduced from Nunivak Island to Cape Thompson (Gunn and Forchhammer 2008, ADFG 2016). As a result of these reintroductions, muskoxen populations now occur on the Seward Peninsula, including Bering Land Bridge National Preserve, and in Noatak National Preserve and Cape Krusenstern National Monument.

The National Park Service (NPS) and Alaska Department of Fish and Game (ADFG) collaborate on muskox population estimation and composition surveys of these populations of muskoxen. To do a population survey, pilots fly planes in long straight lines (transect lines) and pilots and biologists observe and count muskoxen. To do a composition survey, a helicopter is used to drop biologists off close enough to observe muskox groups, but far enough away not to disturb them. Biologists then determine the number of males, females, and yearlings in a group.

On the Seward Peninsula, abundance surveys of the population have been conducted at regular intervals between 1983 and 2015 and composition surveys have been conducted at regular intervals between 2002 and 2015 (Schmidt and Gorn 2013). The population increased from the time of introduction until it plateaued in 2010 and then decreased at a rate of 14% per year through 2012 (Schmidt and Gorn 2013). One hypothesis for the decline is that the harvest of mature males from the population may have changed the defensive behavior of groups, thereby leaving them more vulnerable to predation (Schmidt and Gorn 2013).

In response to changes in hunting regulations and harvest rates of <2%, the most recent data show that between the 2012 and 2015 the population across the Seward Peninsula appeared to stabilize (Gorn 2015). The number of animals within Bering Land Bridge National Preserve and adjacent areas, however, declined during the same time period. This localized decline poses population management challenges. The 2015 population-level survey found the recruitment rate (the number of young animals born into the population that survive to an age between 1-2 years old) to be low (8% of the population; Gorn 2015). Muskoxen are now found in suitable habitat throughout the Seward Peninsula, however, they appear to be emigrating to areas outside of Bering Land Bridge National Preserve and expanding their range into the Nulato Hills.

Since 1988, population estimates and composition surveys have been conducted at regular intervals on the Cape Thompson muskoxen population in what is called the “core area” in and adjacent to Cape Krusenstern National Monument. The core area comprises an area within 30 km of the shore from the mouth of the Noatak River northwest to Cape Lisburne (Figure 1). Since 2004, the Cape Thompson population has declined in the core area or is shifting eastward into what has been called the “expanded area” in Noatak National Preserve (Schmidt and Westing 2011).

^{Above: Figure 1. Survey areas for muskoxen showing areas surveyed on the Seward Peninsula and the core and expanded areas of the Cape Thompson population (adapted from Schmidt and Gorn 2013). Black lines indicate locations of transects flown during the 2011 and 2016 Cape Thompson muskox survey. The “core area” is outlined in green and the “expanded area” is pink and blue (adapted from Schmidt and Westing 2011).}

In 2011, the suspected shift in the Cape Thompson muskoxen population distribution prompted the NPS and ADFG to survey and generate a population estimate for the whole Cape Thompson population in both the core and expanded areas. The results showed that at least half of the Cape Thompson population resided in the expanded area.

There has been increased interest to expand subsistence hunting opportunity in the Cape Thompson population. Also, recent concern about the overharvest of adult bulls and subsequent declines in muskoxen populations (Schmidt and Gorn 2013) has led to the need for more frequent and precise estimates of abundance and sex and age composition of the population.

A group of muskox cows, yearlings, and young bulls.

NPS Photo / Hillary Robison

To this end, the expanded survey was repeated in March 2016. Comparison of the 2011 and 2016 estimates for the whole population residing in the core and expanded areas indicated that the number of animals did not change over the five-year interval between surveys (Schmidt et al. 2016).

When looking at the data for the population in the core area from 1988 to present, it appears the population residing in the core area declined from a high of about 370 animals in 2005 to around 220-230 animals in 2011 and has stabilized at that level. The proportion of adult males to females within the core population decreased between 2011 and 2016, which gives managers pause for thought on managing muskoxen harvest in this area. Muskoxen are now found in suitable habitat in areas within and adjacent to Cape Krusenstern National Monument, Noatak National Preserve, and north of the Brooks Range.

References

Alaska Department of Fish and Game (ADFG). 2016.
Muskox (Ovibos moschatus) species profile. Available at: http://www.adfg.alaska.gov/index.cfm?adfg=muskox.main (accessed March 4, 2016)

Allen, J. A. 1912.
The probable recent extinction of the muskox in Alaska. Science 36:720-722.

Gorn, T. S. 2015.
Alaska Department of Fish and Game Division of Wildlife Conservation memorandum: 2015 muskox survey results. May 6, 2015. Alaska Department of Fish and Game Division of Wildlife Conservation, Northwest, Nome, Alaska.

Gunn, A. and M. Forchhammer. 2008.
Ovibos moschatus. Available at: http://www.iucnredlist.org/details/29684/0 and http://dx.doi.org/10.2305/IUCN.UK.2008.RLTS.T29684A9526203.en (accessed March 4, 2016)

Lent, P. C. 1988.
Ovibos moschatus. Mammalian Species 302:1-9.

Schmidt, J. H. and C. W. Westing. 2011.
A range-wide assessment of the Cape Thompson muskox population and implications for future distance sampling surveys. NPS and ADFG Report.

Schmidt, J. H. and T. S. Gorn. 2013.
Possible secondary population-level effects of selective harvest of adult male muskoxen. Plos One 8(6): e67493. doi:10.1371/journal.pone.0067493

Schmidt, J. H., H. L. Robison, B. Saito, R. Klimstra, and B. Dunker. 2016.
Assessment of the Cape Thompson Muskox Population 2011-2016. NPS and ADFG Report.

Yang, C., C. Xiang, W. Qi, S. Xia, F. Tu, X. Zhang, T. Moermond, and B. Yue. 2013.
Phylogenetic analyses and improved resolution of the family Bovidae based on complete mitochondrial genomes. Biochemical Systematics and Ecology 48:136-143.