Population demography of high arctic caribou on Banks and Melville Islands

Caribou numbers, Rangifer tarandus pearyi, (excluding calves) on Banks Island were estimated (standard error of the estimate) at 1005 (SE±133) in 1992, 709 (SE±128) in 1994 and 436 (SE±71) in 1998; no paired estimates were different (P<0.05). On Melville Island caribou numbers were similar in 1987 and 1997 with estimates of 729 (SE±104) and 787 (SE±97), respectively. We conducted annual sex and age classification surveys during July on Banks Island from 1994-2000 and on Melville Island from 1998-2000. The number of calves per 100 >two-year-old females ranged from 24.0 in 1994 to 74.3 in 1998 on Banks Island, and from 44.8 in 1999 to 80.0 in 1998 on Melville Island. Recruitment rate ranged from 18.6% during 1997/1998 to 27.5% during 1999/2000 on Banks Island and from 16.7% during 1997/1998 to 25.0% during 1999/2000 on Melville Island. There has been an increasing trend in the rate of recruitment on both islands during the last three years of the study.


Introduction
Peary caribou (Rangifer tarandus pearyi) inhabit the Canadian High Arctic and were designated as an endangered subspecies by the Committee on the Status of Endangered Species in Canada (COSEWIC) in 1991.Current estimates of Peary caribou numbers are lower than the first estimates determined in the 1960s and 1970s.Severe winter weather has been associated with die-offs throughout the High Arctic and is believed to be the major cause of the reduction in numbers (Parker et al., 1975;Gunn, 1992).Unfortunately, data to critically assess causes are lacking.Over much of the Peary caribou range few systematic population surveys have been conducted and the periods between surveys can be measured in decades.Data on estimates of calf production, survival and recruitment are limited (Larter & Nagy, 2000a).Data from Banks Island are a notable excep¬ tion.Nagy et al. (1996) described population demogra¬ phy of Peary caribou on Banks Island from 1982-1992.The decline in numbers over this 10-year period was attributed to the cumulative effects of a com¬ bination of factors including human harvest, wolf predation, interisland movement, severe winters, and possible competition from an increasing muskoxen (Ovibos moschatus) population.Systematic population surveys for Banks Island caribou contin¬ ued through the 1990s, and since 1994, annual sex and age classification surveys have been conducted.An annual quota of 36 male only caribou has been in effect for the community of Sachs Harbour since 1992.This quota was met during 1993-94 but har¬ vest has never exceeded 23 animals in any other year.
There are fewer data on the caribou population of neighbouring Melville Island.Although the Melville and Banks Island caribou populations rep¬ resent two different recovery units in the national Peary caribou recovery strategy, these two popula¬ tions have little genetic differentiation (Zittlau et al., this issue).Annual sex and age classification surveys of the Melville Island caribou population were initi-

Study Area
Banks Island is the most western island in the Canadian Arctic Archipelago and covers an area of approximately 70 000 km 2 (Fig. 1).The climate is Arctic Maritime along coastal areas where weather stations are situated, tending toward Arctic Desert inland (Zoltai et al., 1980 There are four major terrestrial habitats: wet sedge meadow (WSM), upland barren (UB), hummock tundra (HT), and stony barren (SB).WSM are gen¬ erally level lowlands dominated by sedges (Carex aquatilis and Eriophorum scheuchzeri).UB and HT are well-drained sites found on slopes.Vegetation is dominated by mountain avens (Dryas integrifolia) and willow (Salix arctica).HT is characterized by indi¬ vidual vegetated hummocks.SB are sparsely vegetat-ed with a gravely substrate and are found on wind blown areas, ridges, and gravel and sand bars.A more detailed description of the flora of Banks Island can be found in Wilkinson et al. (1976), Porsild &Cody (1980), andZoltai et al. (1980).
Melville Island, located northeast of Banks Island, is the largest island of the Parry Islands group and covers an area of approximately 42 000 km 2 (Fig. 1.).Winters are long and summers cool and short.Although there are no weather stations on Melville Island, records from Mould Bay (76°14'N; 119°20'W) and Resolute Bay (74°43'N; 94°59'W) show that the mean maximum daily temperature is below 0 °C starting in September with mean month¬ ly temperatures of -34 °C in February and 4 °C in July, the coldest and warmest months.The island is geologically divided into three distinct structural provinces (Tozer & Thorsteinsson, 1964).Eastern and central Melville Island (east of 112 °W) is gen¬ erally low, <150 m above mean sea level (amsl), and flat.Western Melville Island is mainly plateau rang¬ ing from 300-600 m amsl with steep walled drainages and some peaks rising to 1100 m amsl.
Vegetation cover is prostrate and generally sparse consisting of lichens, bryophytes, graminoids, herbs, cushion plants and shrubs (Babb & Bliss, 1974;Edlund & Alt, 1989).Babb & Bliss (1974) describe four general cover types: polar desert, polar semidesert, diverse terrain, and wet sedge-moss mead¬ ows.Polar deserts are devoid of woody shrubs and have 0-10% plant cover.Polar semi-deserts may have some moister areas and 5-20% cover of vascular plants including Luzula spp., Papaver spp., Saxifraga spp., and Draba spp.Diverse terrain areas are more mesic than polar semi-deserts.Mats of woody species (Cassiope tetragona, Dryas integrifolia, and Salix arctica) are interspersed throughout and in moist depressional areas patches of moss-graminoid meadows occur.Wet sedge-moss meadows are large areas dom¬ inated by a continuous layer of mosses and sedges or grasses.A more detailed description of the flora of Melville Island can be found in Thomas et al. (1999).
Muskoxen and caribou are resident ungulates on Melville Island.In 1997 the muskoxen population was estimated (standard error of the estimate) at 2258 (SE±268) >one-year-old animals (A.Gunn & J. Dragon, unpubl.data), and had declined since the previous estimate of 4761 (SE±372) in 1987 (Miller, 1988).Arctic wolves, arctic foxes, and polar bears are resident predators.

Methods
Population Estimates Banks Island Islandwide surveys were conducted during summers 1992, 1994, and 1998 and were designed to esti¬ mate muskox and Peary caribou population sizes.Surveys were conducted in July-early August, except in 1992 when the survey was conducted in late August.Censuses were conducted using fixed-wing aircraft (Helio-Courier and Cessna 185) and striptransect techniques with a stratified design; the tran¬ sect was the sampling unit (Norton-Griffiths, 1978).Banks Island was stratified into eight strata based upon a combination of geographic area and muskox density determined from previous surveys (see Fig. 1).Transect lines were flown at fixed altitudes.We attempted to maintain an altitude of 150 m above ground level (agl).Animals were counted within fixed strips on either side of the aircraft.Markers were placed on the aircraft wing struts to bound the strips (following Norton-Griffiths, 1978).Strip width was 500 m on each side of the aircraft.We attempted to maintain an airspeed of 160 km/hr.Each stratum was flown at 20% coverage except for the Egg (E) and Masik (M) (Fig. 1) where cover¬ age was 40%.After the initial islandwide survey was completed, areas of high caribou density were blocked off and reflown at 40% coverage.Population estimates (animals >one-year-old) for all years were derived by the Jolly (1969) method for unequal sized sampling units.We present estimated population number and the standard error of the estimate (Norton-Griffiths, 1978).Observations from the reflown blocks of high caribou density were used for the population estimate.Observations from the orig¬ inal coverage of areas blocked off as high density caribou areas were not included in the population estimate being replaced by the reflown observations.We tested for differences in population estimates between years following the formula described in Norton-Griffiths (1978) and adapted from Cochran (1954).

Melville Island
Islandwide aerial surveys were conducted in 1987 and 1997 to estimate caribou and muskox popula¬ tions (Miller, 1988;A. Gunn & J. Dragon, unpubl. data).Both surveys used a strip-transect technique with a stratified design; the transect was the sam¬ pling unit (Norton-Griffiths, 1978).The island was stratified into 13 strata based upon geographic area (Fig. 1).In 1987, a Bell 206B helicopter was used.
Transect lines were flown at 90 m agl and an airspeed of 160 km/hr.Parallel lines were flown 6.4 km apart; animals were counted within fixed strips of 857 m on each side of the aircraft resulting in an overall coverage of 27% (Miller, 1988).In 1997, a fixedwing aircraft (Helio-Courier) was used.Transect lines were flown at 100 m agl at an airspeed of 160 km/hr.Parallel lines were flown that provided an overall coverage of 20% with animals being counted within fixed strips of 500 m on each side of the air¬ craft (A.Gunn & J. Dragon, unpubl.data).
Population estimates (animals >one-year-old) for both surveys were derived by the Jolly (1969) method for unequal sized sampling units.We pres¬ ent estimated population number and the standard error of the estimate (Norton-Griffiths, 1978).

Classification Surveys Banks Island
Surveys were conducted annually during July from 1994-2000.Three to six h flights were made by hel¬ icopter aircraft (Bell 206B or 206L) over the major historical calving and summer range located to the northwest of Banks Island (Urquhart, 1973).Caribou were spotted from the air and the survey crew, generally an observer and a recorder, was posi¬ tioned on the ground in such a way as to minimize disturbance of the animals.The survey crew moved into a position where the animals could be observed with a spotting scope (15-45x) or binoculars (7x24).
Caribou were classified into calves, yearlings, adult females (>two-years-old), and adult males (>twoyears-old).Occasionally, small groups of adult males (one-three) or dam-calf pairs were classified from the air.In 1994 and 1998, aerial reconnaissance by fixed-wing aircraft involved in the Banks Island pop¬ ulation survey identified areas of local caribou con¬ centration in the summering grounds prior to the classification survey and the helicopter flew directly to these areas.

Melville Island
Surveys were conducted annually in mid-July from 1998-2000.In 1998, the survey was based on oppor¬ tunistic observations made during flights with a rotary aircraft (Bell 206L) concentrated over the Dundas Peninsula (Fig. 1; VI).This was in an area where Miller et al. (1973) had reported high densi¬ ties of Peary caribou in August, 1972.In 1999, we flew over a much larger area of central and western Melville Island in an attempt to confirm that the majority of caribou were distributed on Dundas Peninsula during mid-July (Larter & Nagy, 2000b); the flight confirmed this.We blocked off a survey area bounded by 74°46'N to the north and 74°32'N to the south and flew eight parallel line transects, 26 km in length and spaced ca.5.6 km apart, from 113°40'W eastward to 112°23'W.All groups of caribou observed within this area and during flights to and from the survey area were classified as described above.During the 2000 survey we added a ninth parallel transect to the east of the survey area on 112°12'W.

Demographic characteristics
We estimated calf production as the number of calves per 100 adult females determined in the July classification surveys.We realize that this estimate does not address neonatal mortality but surveys were conducted during the same three-week period in July and we believe any biases would be similar for each survey.We used the number of yearlings per 100 adult females divided by the sum of 100 plus the number of yearlings per 100 adult females to estimate annual recruitment rate, which we expressed as a percent.Because fewer than 15 ani¬ mals were classified during the 1995 survey on Banks Island (Table 1), we made no estimates of pro- duction or recruitment for this year.The four unknown adults from the 1997 survey on Banks Island (Table 1) were also excluded from the calcula¬ tions.We used correlation analysis to assess any potential trends in calf production and recruitment rate over time for Banks and Melville Islands.

Discussion
Although current pop¬ ulation estimates of Banks and Melville Island caribou are lower than those of 20 years ago, both popula¬ tions have remained relatively stable since 1987 for Melville and since 1991 for Banks Island (Nagy et al., 1996).Annual calf production has been highly variable for both populations.The slight increasing trend in calf pro¬ duction on Banks Island is likely a result of low calf production in 1994.Larter & Nagy (2000a) docu¬ mented 11 years of calf production on Banks Island and production in 1994 was the lowest recorded.The decreasing trend in calf production on Melville Island is likely a result of small sample size (three years) in combination with annual variability.Values reported for Melville Island fall well within those reported for Banks Island and other high arctic cari¬ bou and Svalbard reindeer populations reported else¬ where (Tyler, 1987;Miller, 1992).
High calf production does not necessarily translate into high recruitment.Calf mortality is one of the main factors affecting population growth of caribou and reindeer populations (Bergerud, 1971;Parker, 1972;Skogland, 1985;Tyler, 1987).Calf production and calf survival are both components of recruitment rate, therefore recruitment rate may provide better information on the potential for population change as our data suggest.Since 1998, the recruitment rate for both populations has shown a positive trend.Winter 1997/1998 was one of the mildest in recent years and had the least severe snow conditions, par¬ ticularly snow depth, recorded on Banks Island dur¬ ing the period 1992/1993 to 1997/1998 (Larter & Nagy, 2000c;2001a;R. Kuptana pers. comm).Whether snow conditions on Melville Island were of lesser severity during winter 1997/1998 is unknown.
During winter, legumes (Astragalus spp.and Oxytropis spp.) are an important dietary item for Banks Island caribou with their proportion in the diet being greater during years of shallower snow depth (Larter & Nagy 1997; N. Larter & J. Nagy unpubl.data).Shallower snow likely increases legume availability.During winter legumes remain highly digestible, and have a high crude protein con¬ tent (ca.13%), much higher than sedge and moun¬ tain avens which make up much of the remaining proportion of the winter diet (Larter & Nagy, 2001b).Improved access to a high quality winter diet may have had a positive effect on overwinter sur¬ vival and/or calf production, which translated into increased recruitment.Whether improved access to a high quality winter diet continued during winters following 1997/1998 is unknown as comparative snow data collection ended.
The effect of wolf predation on these caribou pop¬ ulations remains unknown.Both Banks Island and neighbouring Victoria Island have a substantial alternate prey source, i.e. large muskoxen popula¬ tions, which could sustain substantial wolf numbers.Harvest records and observations from local residents of both Sachs Harbour (Banks Island) and Holman (NW Victoria Island) indicate that wolf numbers have been increasing throughout the 1990s (Nagy & Larter, 2000;N. Larter & J. Nagy, unpubl. data).Between 40 and 50 wolves are generally observed on whole island surveys of Banks Island and it is not uncommon to observe groups of 15¬ 20 individuals.The alternate prey source is not as substantial on Melville Island, how¬ ever during the whole island survey in 1997, 20 adult wolves and 12 pups were observed (A.Gunn & J. Dragon, unpubl. data).
Limited information on wolf diet from Banks and Melville Island shows that muskoxen predominates (Nagy & Larter, 2000).However, wolf diet has been determined from opportunistic collec¬ tions of wolf scats and the stomachs from harvested wolves, mostly collected during winter.Such sam¬ pling may not address wolf diet at key times of the year and from key locations.For example, on Banks Island, when caribou make their southerly migration from the calving and summer range (NW Banks Island), they pass adjacent to a high wolf density area.Non-selective predation on calves, yearlings, and adult females as caribou migrate through this area could go undetected by the current sampling regime.Nor would this type of predation be notice¬ able in our estimates of production or recruitment.Therefore, it is crucial that whole island population surveys be conducted at regular intervals so that pro¬ duction and recruitment estimates can be evaluated in their proper context.

Fig. 1 .
Fig. 1.The study area, Banks and Melville Islands in the western Arctic Archipelago.Note: Banks Island is delineated into the eight survey strata: A, B, C, D, E (Egg), M (Masik), T (Thomsen), and P (Parker).Melville Island is delineated into the 13 survey strata.