Subsections:
Status of the Central Arctic Herd
Development-related Changes in Distribution

From the mid-1970s through the mid-1980s, use of calving and summer habitats by Central Arctic herd caribou (Rangifer tarandus granti) declined near petroleum development infrastructure on Alaska’s arctic coastal plain (Cameron et al. 1979; Cameron and Whitten 1980; Smith and Cameron 1983; Whitten and Cameron 1983a, 1985; Dau and Cameron 1986).

With surface development continuing to expand westward from the Prudhoe Bay petroleum development area (Fig. 4.1), concerns arose that the resultant cumulative losses of habitat would eventually reduce productivity of the caribou herd. Specifically, reduced access of adult females to preferred foraging areas might adversely affect growth and fattening (Elison et al.1986; Clough et al. 1987), in turn depressing calf production (Dauphiné 1976, Thomas 1982, Reimers 1983, White 1983, Eloranta and Nieminen 1986, Lenvik et al. 1988, Thomas and Kiliaan 1991) and survival (Haukioja and Salovaara 1978, Rognmo et al. 1983, Skogland 1984, Eloranta and Nieminen 1986, Adamczewski et al. 1987).

Figure 4.1. Petroleum development infrastructure in the Prudhoe Bay and Kuparuk petroleum development areas, Alaska, showing primary and secondary roads, pipelines, and gravel pads, 1994.

Those concerns, though justified in theory, lacked empirical support. With industrial development in arctic Alaska virtually unprecedented, there was little basis for predicting the extent and duration of habitat loss, much less the secondary short- and long-term effects on the well-being of a particular caribou herd.

Furthermore, despite a general acceptance that body condition and fecundity of the females are functionally related for reindeer and caribou, it seemed unlikely that any single model would apply to all subspecies of Rangifer, and perhaps not even within a subspecies in different geographic regions. We therefore lacked a complete understanding of the behavioral responses of arctic caribou to industrial development, the manner in which access to habitats might be affected, and how changes in habitat use might translate into measurable effects on fecundity and herd growth rate.

Our study addressed the following objectives: 1) estimate variation in the size and productivity of the Central Arctic herd; 2) estimate changes in the distribution and movements of Central Arctic herd caribou in relation to the oil field development; 3) estimate the relationships between body condition and reproductive performance of female Central Arctic herd caribou; and 4) compare the body condition, reproductive success, and offspring survival of females under disturbance-free conditions (i.e., east of the Sagavanirktok River) with the status of those exposed to petroleum-related development (i.e., west of the Sagavanirktok River).

Photocensus results indicate net growth of the Central Arctic herd from 1978 through 2000 (Fig. 4.2). Within that long-term trend, however, there was an abrupt decrease from 1992 to 1995. This decrease coincided with calf production estimates at or below approximately 70%. Steady growth thereafter was associated with productivity estimates consistently exceeding 70%.

Figure 4.2. Photocensus estimates of the Central Arctic caribou herd, 1978-2000 [Whitten and Cameron 1983b; Alaska Department of Fish and Game (ADF&G) files] and net calf production based on observations of radio-collared adult (i.e., sexually-mature) females from 10 June through 15 August (ADF&G files). Note: Productivity data not adjusted for differences in sample sizes east and west of the Sagavanirktok River, Alaska.

Since 1978, changes in the distribution of calving caribou associated with the Kuparuk petroleum development area, west of Prudhoe Bay (Fig. 4.1), have been quantified using strip-transect surveys flown by helicopter.

After construction of a road system near Milne Point, mean caribou abundance declined by more than two-thirds within 2 km from a road and was less than expected, overall, within 4 km; but nearly doubled 4-6 km from roads (Fig. 4.3) (Cameron et al. 1992b). Prior to road placement, caribou were found in a single, more-or-less continuous concentration roughly centered where the Milne Point Road was subsequently built. After construction of the road, a bimodal distribution with separate concentrations east and west of the road was clearly apparent (Fig. 4.4) (Smith and Cameron 1992), indicating avoidance of infrastructure by calving caribou.

Figure 4.3. Fractional changes in mean density of caribou from the Central Arctic herd between pre-construction (1978-81) and post-construction (1982-87) periods for 1-km-distance intervals from the Milne Point road system in the Kuparuk petroleum development area, Alaska. (from Cameron et al. 1992b)

Figure 4.4. Changes in mean relative distribution of caribou from the Central Arctic herd in the Kuparuk petroleum development area, Alaska, during calving: 1979-1981, 1982-1986, and 1987-1990. Shown only are those 10.4-km2-transect segments in which the occurrence of caribou exceeded the area contribution to total coverage (0.9%). Gradations in line spacing depict multiples of observed use relative to availability: wide = <3X; narrow = >3X-5X; solid = >5X. (from Smith and Cameron 1992)

These results suggest that roads spaced too closely will depress calving activity within the entire oil field complex. In fact, relative occurrence of caribou in the heavily-developed western portion of the Kuparuk petroleum development area declined significantly from 1979 through 1987, independent of total abundance (Fig. 4.5) (Cameron et al. 1992b).

Figure 4.5. Decline in percentage abundance of caribou from the Central Arctic herd west of the Milne Point Road, Kuparuk petroleum development area, Alaska (Spearman’s Rank, P < 0.02), and changes in total numbers of caribou observed north of the Spine Road (see Fig. 4.3), 1979-1987. (from Cameron et al. 1992b)

An exponential decline in the occurrence of caribou as density of roads increased (Fig. 4.6) (Nellemann and Cameron 1998) underscores the sensitivity of the females during the calving period. The probable consequence is reduced access to preferred habitats (Bishop and Cameron 1990, Nellemann and Cameron 1996, 1998).

Figure 4.6. Relationship between mean (SE) density of caribou from the Central Arctic herd and road density within preferred rugged terrain, Kuparuk petroleum development area, Alaska, 1987-1992. Different letters indicate a significant difference (P < 0.05). (from Nellemann and Cameron 1998)

Incremental redistribution and local habitat loss within the Kuparuk petroleum development area may have triggered changes on a regional scale. Wolfe (2000) reported an inland shift in concentrated calving activity away from the Milne Point petroleum production unit (Fig. 4.7), apparently in response to the increasing density of infrastructure.

Figure 4.7. Shifts in concentrated calving areas, Central Arctic caribou herd, Alaska, 1980-1995. (adapted from Wolfe 2000)

Ground observations within the Kuparuk petroleum development area in 1978-1990 provided additional insights on changing distribution and movements. Caribou increasingly avoided zones of intensive activity, especially during the calving period (Smith et al. 1994), corroborating data from strip-transect surveys. Lower success in crossing road/pipeline corridors by large insect-harassed groups (Smith and Cameron 1985, Curatolo and Murphy 1986, Murphy and Curatolo 1987, Murphy 1988) may have contributed to a general shift from the central Kuparuk petroleum development area to peripheral areas with less surface development and human activity. Routes of summer movement are now primarily south of Oliktok Point and along the Kuparuk River floodplain (Smith et al. 1994).

An analysis of the summer distribution of radio-collared females in 1980-1993 (Cameron et al. 1995) suggests that caribou use of the oil field region at Prudhoe Bay has declined considerably from that noted during the 1970s by Child (1973), White et al. (1975), and Gavin (1978). Caribou abundance within the main industrial complex as well as east-west movements through that area were significantly lower than for other areas occupied by caribou along the arctic coast (P = 0.001 and P < 0.001, respectively). Conservative calculations yielded an estimated 78% decrease in use by caribou and a 90% decrease in their lateral movements (Cameron et al. 1995), all changes apparently in response to intensive development of the Prudhoe Bay to Kuparuk oil field region over the past 3 decades. Occurrence of caribou that use the complex, however, is reportedly unrelated to distance from infrastructure (Cronin et al. 1998).

(continued to Part 2)

| Home | Section 1 - Introduction | Section 2 - Land Cover | Section 3 - Porcupine Caribou Herd |
| Section 4 - Central Arctic Caribou Herd | Section 5 - Forage Quantity and Quality | Section 6 - Predators |
| Section 7 - Muskoxen | Section 8 - Polar Bears | Section 9 - Snow Geese | Acknowledgements |