Population survey of Peary caribou ( Rangifer tarandus pearyi ) and muskoxen ( Ovibos moschatus ) on Banks Island , Northwest Territories , July 2010

We conducted a systematic aerial transect survey of Peary caribou (Rangifer tarandus pearyi) and muskoxen (Ovibus moschatus) on Banks Island, Northwest Territories, in July 2010. !e population estimate of adult Peary caribou was 1097 ± 343 (95% Con#dence Interval: CI), which is not signi#cantly di$erent from the 2005 estimate of 929 ± 289 (95% CI; P < 0.05). !e current number, however, is a 4to 9-fold decrease since the 1980s. !e adult muskoxen population estimate was 36 676 ± 4031 (95% CI), which is signi#cantly lower than the 2005 estimate of 47 209 ± 3997 (95% CI; P < 0.05).


Introduction
Peary caribou (Rangifer tarandus pearyi) are endemic to Canada, occurring in the high Arctic islands of the Northwest Territories (NWT) and Nunavut.Peary caribou have declined across their entire range since the rst surveys were done in the 1960s and 1970s, however, surveys of Peary caribou have been conducted infrequently, which makes determining trend of the overall Peary caribou population di cult.e Peary caribou of Banks Island, however, have a long term aerial strip-transect survey data set.Surveys were rst conducted on Banks Island in 1973, and systematic island-wide surveys using xed-wing aircraft have been done every 2 -5 years since 1982.ese have documented the number and population trend of Peary cari-bou and muskoxen on Banks Island.Between 1982 and1998, the

Brief Communication
For muskoxen, there is both a commercial and aboriginal subsistence harvest.Although the total annual allowable harvest of muskoxen is 10 000, reported harvests have ranged from 60 to 987 muskoxen per year for the period 2005 -2010.Here we present the 2010 population estimates for Peary caribou and muskoxen on Banks Island in relation to past estimates.

Study area
Banks Island covers an area of 70 579 km 2 , making it the 4th largest island in the Canadian Arctic Archipelago.Located in the Inuvialuit Settlement Region (ISR), Banks Island is home to both Peary caribou and muskoxen.Wildlife on Banks Island is co-operatively managed by the Wildlife Management Advisory Council (WMAC [NWT]), made up of members appointed by the Inuvialuit, Government of the NWT, and the Government of Canada and whose mandate includes advising appropriate Ministers on all matters relating to wildlife management within the ISR.

Methods
Survey lines, spaced 5 km apart, were own over the entire island.
e survey was conducted with two aircraft (Helio Courier and a Cessna 206) and each crew consisted of a pilot, two rear seat observers, and a front seat recorder/navigator.e island was divided into 11 blocks for survey purposes (A -K). is ensured that survey lines could be own in less than 30 minutes to reduce observer fatigue.Transects were run perpendicular to drainages.
e survey was own at an average speed of approximately 160 km/hr, 120 m above ground level and markers were placed on the aircraft struts or windows to delineate a strip width of 500 m on each side of the aircraft.e pilot maintained altitude using an aircraft altimeter.No correction factor was used for missed or over-counted animals due to inability to maintain survey altitude due to steep terrain. is type of terrain on Banks Island is minimal and occurs mostly in the northwest portion of the island.Past surveys also did not have a correction factor and covered the same terrain with similar methods so would have similar biases.Observations within 500 m were considered 'on' transect.Muskoxen and caribou, on or o transect, were classi ed as adults (≥ 1-year old) or calves based on body size as calves are noticeably smaller than adult animals.Further, all caribou observed were classi ed as mature bulls, cows/young bulls, or calves.Mature bulls were identi ed by their antlers, and cows and young bulls were grouped as distinguishing between them from the aircraft is more di cult.Animals directly under the aircraft, and not visible from the side window, were considered 'o transect' as transect widths were measured using the area visible to the observer from the side of the aircraft.Sightings of other wildlife were also recorded.
Population estimates for adult caribou and muskoxen were calculated using a ratio method for unequal-sized units sampled without replacement (Krebs, 1999; Ecological Methodology, Version 7.0).Population estimates are calculated for the adults because of the high variability of caribou calf production yearto-year and higher mortality rate in their rst year (Larter & Nagy, 1999b). is is also consistent with historic population estimates.A two-tailed t-test was used to determine if the population estimates of adult muskoxen and Peary caribou were signi cantly di erent than the 2005 estimates (Gasaway et al., 1986;Nagy et al., 2009a).

Results & Discussion
e survey was conducted between July 17 and 26, 2010.One survey crew ew blocks A, B, C, H, I, J, and K in 9 days, with one weather day (19th July).e other survey crew ew blocks D, E, F, and G in 7 days with no weather days once the survey started.All planned survey lines were own except a short segment on the north shore of the island, which was obscured by fog (Fig. 1).ere were 229 transects totaling 13 826.8km in length own on survey.With a transect width of 1 km this results in a coverage of 19.59% of the island.
A total of 285 Peary caribou (215 adults, 70 calves) were seen on transect, and a further 75 caribou (63 adults, 12 calves) were seen o transect (Fig. 1).On transect observations resulted in a population estimate of 1097 ± 343 (95% Con dence Interval, [CI]; CV = 0.313) adult Peary caribou on Banks Island.e proportion of calves among all caribou observed (on and o transect as all observations of caribou were classi ed) was 22.8%.
e proportion of calves varies by survey, reported in 2005, 2001, and 1992as 19.4%, 26.3% and 28.8%, respectively (Nagy et al., 2006;;2009a;b).Eighty-one mature bulls were observed (on and o transect), which was 22.5% of all caribou observed.e proportion of mature bulls varies by survey, reported in 2005 and 2001 as 29% and 19%, respectively (Nagy et al., 2006;2009a).Distribution was concentrated in the northwest, northeast, and central portions of Banks Island (Fig. 1).e average group size for Peary caribou observed on transect was 4.2 with the largest group being 37 and smallest being one.e 2010 population estimate of Peary caribou was not signi cantly di erent from the 2005 estimate of 929 ± 289 (95% CI) (t = 0.74, P < 0.05, df = 45).Peary  caribou numbers on Banks Island have decreased 9-fold since 1982; however, the current low abundance appears to have been stable for the past decade (Fig. 2).At small numbers populations become more vulnerable (Lacy, 2000) and at low numbers Peary caribou populations are particularly in uenced by severe weather and changes in their environment (Gunn et al., 1980).
e average group size for muskoxen observed on transect was 8.5 with the largest group being 38 and smallest being one.
ere were a total of 8054 muskoxen (7185 adults, 869 calves) observed on transect, resulting in a population estimate of 36 676 ± 4031 (95% CI; CV=10.99)adult muskoxen on Banks Island and a calf percentage of 10.7%.Muskoxen were spread throughout Banks Island, with concentrations in the southwest and north-central areas (Fig. 3).e 2010 population estimate of adult muskoxen was signi cantly lower (t = 3.699, P < 0.05, df = 90) than the 2005 estimate of 47 209 ± 3997.Muskoxen abundance on Banks Island from 1982 to 2010 has uctuated, and since 2001 has exhibited a decline (Fig. 4).
e reasons for the decline are not clear.In 1996 a die-o of muskoxen on Banks Island was attributed to disease (Larter & Nagy, 1999a).During  the July 2004 survey a large number of muskoxen carcasses were observed and calves made up only 4% of total muskoxen observed during the survey.is was assumed due to severe icing events in the 2003/2004 winter (Nagy & Gunn, 2009).Our 2010 survey observed only four carcasses, and 10.7% calves is similar to the recovered productivity of 12.6% observed in 2006 (Gunn & Williams, unpublished data, Government of the NWT July 2006).As designed, the surveys provided abundance estimates and trends, while explanations behind trends must be sought elsewhere.

Fig. 1 .
Fig. 1.Distribution of adult Peary caribou observed both on and of transect during an aerial servey own from July 17 -26, 2010, on Banks Island, NWT.

Fig. 2 .
Fig. 2. Transects own during the 2010 survey and distribution of adult caribou found 'on' and 'o ' transect on northwest Banks Island, NWT.

Fig. 3 :
Fig. 3: Population counts of adult Minto Inlet Peary caribou and Dolphin-Union caribou on northwest Banks Island, NWT with 95% con dence intervals around the population estimates.

Fig. 4 .
Fig. 4. Transects own during the 2010 survey and distribution of adult muskoxen found 'on' transect on northwest Banks Island, NWT.
Canada in May 2004 and legally listed under the Species at Risk Act in February 2011.