Central Arctic Caribou and Petroleum Development: Distributional, Nutritional, and Reproductive Implications

Abstract

We synthesize findings from cooperative research on effects of petroleum development on caribou (Rangifer tarandus granti) of the Central Arctic Herd (CAH). The CAH increased from about 6000 animals in 1978 to 23 000 in 1992, declined to 18 000 by 1995, and again increased to 27 000 by 2000. Net calf production was consistent with changes in herd size. In the Kuparuk Development Area (KDA), west of Prudhoe Bay, abundance of calving caribou was less than expected within 4 km of roads and declined exponentially with road density. With increasing infrastructure, high-density calving shifted from the KDA to inland areas with lower forage biomass. During July and early August, caribou were relatively unsuccessful in crossing road/pipeline corridors in the KDA, particularly when in large, insect-harassed aggregations; and both abundance and movements of females were lower in the oil field complex at Prudhoe Bay than in other areas along the Arctic coast. Female caribou exposed to petroleum development west of the Sagavanirktok River may have consumed less forage during the calving period and experienced lower energy balance during the midsummer insect season than those under disturbance-free conditions east of the river. The probable consequences were poorer body condition at breeding and lower parturition rates for western females than for eastern females (e.g., 1988 - 94: 64% vs. 83% parturient, respectively; p = 0.003), which depressed the productivity of the herd. Assessments of cumulative effects of petroleum development on caribou must incorporate the complex interactions with a variable natural environment.

Full text

ARCTIC
VOL. 58, NO. 1 (MARCH 2005) P. 1– 9
Central Arctic Caribou and Petroleum Development:
Distributional, Nutritional, and Reproductive Implications
RAYMOND D. CAMERON,
1,2
WALTER T. SMITH,
1
ROBERT G. WHITE
3
and BRAD GRIFFITH
4
(Received 15 October 2002; accepted in revised form 11 May 2004)
ABSTRACT. We synthesize findings from cooperative research on effects of petroleum development on caribou (Rangifer
tarandus granti) of the Central Arctic Herd (CAH). The CAH increased from about 6000 animals in 1978 to 23000 in 1992,
declined to 18000 by 1995, and again increased to 27000 by 2000. Net calf production was consistent with changes in herd size.
In the Kuparuk Development Area (KDA), west of Prudhoe Bay, abundance of calving caribou was less than expected within
4 km of roads and declined exponentially with road density. With increasing infrastructure, high-density calving shifted from the
KDA to inland areas with lower forage biomass. During July and early August, caribou were relatively unsuccessful in crossing
road/pipeline corridors in the KDA, particularly when in large, insect-harassed aggregations; and both abundance and movements
of females were lower in the oil field complex at Prudhoe Bay than in other areas along the Arctic coast. Female caribou exposed
to petroleum development west of the Sagavanirktok River may have consumed less forage during the calving period and
experienced lower energy balance during the midsummer insect season than those under disturbance-free conditions east of the
river. The probable consequences were poorer body condition at breeding and lower parturition rates for western females than for
eastern females (e.g., 1988–94: 64% vs. 83% parturient, respectively; p = 0.003), which depressed the productivity of the herd.
Assessments of cumulative effects of petroleum development on caribou must incorporate the complex interactions with a variable
natural environment.
Key words: behavior, body condition, calving, cumulative effects, demography, fecundity, habitat, Rangifer
RÉSUMÉ. On a procédé à une synthèse des résultats de travaux de recherche coopérative concernant les effets de l’exploitation
pétrolière sur le caribou (Rangifer tarandus granti) formant la harde du centre de l’Arctique (HCA). La population de celle-ci est
passée de 6000 têtes en 1978 à 23000 en 1992, puis a diminué à 18000 en 1995 pour augmenter de nouveau à 27 000 en 2000.
La production nette des veaux allait de pair avec les changements dans la taille de la harde. Dans la zone de développement de
Kuparuk (KDA), située à l’ouest de Prudhoe Bay, l’abondance des caribous qui mettaient bas était inférieure à celle prévue dans
une bande de 4 km de part et d’autre des routes, et elle déclinait de façon exponentielle avec la densité routière. Avec une
augmentation des infrastructures, on assistait à un déplacement du vêlage à forte densité de la KDA vers des zones de l’intérieur
ayant une biomasse de fourrage moins importante. Durant juillet et au début d’août, il était assez rare que les caribous réussissent
à traverser les corridors routiers/pipeliniers dans la KDA, surtout lorsqu’ils formaient de vastes agrégations harcelées par les
insectes; l’abondance de même que les déplacements des femelles étaient en outre moindres au sein du complexe pétrolier de
Prudhoe Bay qu’à d’autres endroits situés le long du rivage arctique. Il est possible que les femelles qui étaient exposées à
l’exploitation pétrolière à l’ouest de la rivière Sagavanirktok aient consommé moins de fourrage au cours de la période de vêlage
et que, durant la saison des insectes au milieu de l’été, elles aient connu une balance énergétique inférieure à celle des femelles
vivant sans perturbations à l’est de la rivière. Les conséquences probables étaient un état corporel de qualité inférieure au moment
de l’accouplement, et des taux de parturition plus faibles pour les femelles situées à l’ouest que pour celles situées à l’est (p. ex.,
de 1988 à 1994: 64 % c. 83 % de parturientes respectivement: p = 0,003), faisant ainsi baisser la productivité de la harde. Les
évaluations des effets cumulatifs de l’exploitation pétrolière sur le caribou doivent intégrer les interactions complexes avec un
environnement naturel variable.
Mots clés: comportements, état corporel, vêlage, effets cumulatifs, démographie, fécondité, habitat, Rangifer
Traduit pour la revue Arctic par Nésida Loyer.
1
Alaska Department of Fish and Game, 1300 College Road, Fairbanks, Alaska 99701-1599, U.S.A.
2
Present address: Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, Alaska 99775, U.S.A.; ffrdc@uaf.edu
3
Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, Alaska 99775, U.S.A.
4
USGS Alaska Cooperative Fish and Wildlife Research Unit, University of Alaska Fairbanks, Fairbanks, Alaska 99775, U.S.A.
© The Arctic Institute of North America

2 • R.D. CAMERON et al.
INTRODUCTION
From the mid-1970s through the mid-1980s, use of calving
and midsummer habitats by Central Arctic Herd (CAH)
caribou (Rangifer tarandus granti) declined near oil field
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 continu-
ing to expand westward from the Prudhoe Bay oil field
complex (Fig. 1), concerns arose that the resultant cumu-
lative losses of habitat would eventually reduce productiv-
ity of the 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; Tho-
mas, 1982; Reimers, 1983; White, 1983; Eloranta and
Nieminen, 1986; Lenvik et al., 1988; Thomas and Kiliaan,
1998) and calf survival (Haukioja and Salovaara, 1978;
Rognmo et al., 1983; Skogland, 1984; Eloranta and
Nieminen, 1986; Adamczewski et al., 1987).
Those concerns, though justified in theory, lacked em-
pirical 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
females are functionally related for reindeer (R. t. tarandus)
and caribou, it seemed unlikely that any single model
would apply to all subspecies of Rangifer, or even within
a subspecies, to all geographic regions. We therefore
lacked a complete understanding of the behavioral re-
sponses of Arctic caribou to industrial development, the
manner in which access to various habitats might be
affected, and how changes in habitat use might translate
into effects on fecundity and herd growth.
Our studies had four objectives: 1) to estimate variation
in the size and productivity of the CAH; 2) to estimate
changes in the distribution and movements of CAH cari-
bou in relation to oil field development; 3) to estimate the
relationships between body condition and reproductive
N
FIG. 1. Roads and facilities in the Kuparuk Development Area (west of the Kuparuk River) and Prudhoe Bay oil field complex (east of the Kuparuk River), Alaska,
ca. 1990 (Cameron et al., 1995; reprinted with permission from Rangifer).

ARCTIC CARIBOU AND PETROLEUM DEVELOPMENT • 3
performance of female CAH caribou; and 4) to compare
the body condition and reproductive success 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) (Fig. 1).
Status of the Central Arctic Herd
Photocensus results indicate net growth of the CAH
from 1978 through 2000 (Fig. 2). Within that long-term
trend, however, was a decrease from 1992 to 1995, which
coincided with calf production estimates at or below ap-
proximately 70%. Calf production was also relatively low
during 1989–91, suggesting that herd growth had deceler-
ated or ceased before the 1992 census. Otherwise, periods
of apparent growth were associated with productivity
estimates exceeding 70%.
Development-Related Changes in Distribution
Because the CAH is in contact with industrial develop-
ment from calving time through midsummer, our surveys
focused on those two intervals. The calving period is the
three-week interval beginning with the peak of calving,
i.e., after 50% of the calving has occurred (Russell et al.,
2002:31); for the CAH, this peak usually occurs in early
June (Cameron et al., 1993). The summer insect season
follows, generally extending from late June through early
August (White et al., 1975; Dau, 1986).
Changes in the distribution of calving caribou associ-
ated with the Kuparuk Development Area (KDA), west of
the Kuparuk River (Fig. 1), were quantified by means of
strip-transect surveys conducted from a helicopter. After
construction of a road system between Milne Point and the
Spine Road (Fig. 1), mean caribou abundance declined by
more than two-thirds within 2 km of roads and was less
than expected, overall, within 4 km, but nearly doubled
4–6 km from roads (Fig. 3). Before road construction,
caribou were found in a single, more or less continuous
concentration that encompassed the area where roads would
subsequently be built. After road construction, a bimodal
distribution was clearly apparent, with separate concentra-
tions to the west and east of the road (Fig. 4), indicating
avoidance of infrastructure by calving caribou.
These results suggest that roads spaced too closely will
depress calving activity within portions of an oil field
complex. In fact, relative abundance of caribou in the
heavily developed western portion of the KDA showed a
significant decline from 1979 through 1987, which was
independent of total abundance (Fig. 5). Such declines
FIG. 2. Photo-census estimates of the Central Arctic caribou herd, 1978–2000
(Whitten and Cameron, 1983b; Alaska Department of Fish and Game files) and
net calf production based on observations of radio-collared adult (i.e., sexually
mature) females from 10 June through 15 August (Alaska Department of Fish
and Game files). Note: Productivity data are not adjusted for differences in
sample sizes east and west of the Sagavanirktok River.
FIG. 3. Changes in mean density of calving caribou from the Central Arctic
Herd from 1978–81 (before road construction) to 1982– 87 (after road
construction) at distances of 0–6 km (in 1 km intervals) from the Milne Point
road system, Kuparuk Development Area, Alaska (Cameron et al., 1992b;
reprinted with permission from Arctic).

4 • R.D. CAMERON et al.
apparently involve an exponential decrease in caribou
density with increasing road density (Fig. 6). The probable
consequence is reduced access to preferred foraging habi-
tats (Nellemann and Cameron, 1996, 1998).
Incremental redistribution and local habitat loss within
the KDA may have triggered changes on a regional scale.
Wolfe (2000) reported an inland shift of concentrated calving
activity away from the Milne Point area (Fig. 7), which
coincided with an increase in the density of infrastructure.
Ground observations within the KDA provided addi-
tional insights on changing distribution and movements.
During 1978–90, observations that caribou increasingly
avoided zones of intensive construction and production-
related activity, especially during the calving period (Smith
et al., 1994), corroborated data from strip-transect sur-
veys. Lower success in crossing road/pipeline corridors by
large, insect-harassed groups during summer (Smith and
Cameron, 1985; Curatolo and Murphy, 1986; Murphy and
Curatolo, 1987; Murphy, 1988) may have contributed to
relatively greater use of peripheral areas with less surface
development and human activity. Primary routes of sum-
mer movement have shifted to areas south of Oliktok Point
and along the Kuparuk River floodplain (Smith et al.,
1994).
An analysis of the summer distribution of radio-col-
lared females during 1980–93 (Cameron et al., 1995)
suggested that caribou use of the oil field region at Prudhoe
Bay had declined considerably from that noted by Child
FIG. 4. Changes in mean relative distribution of caribou from the Central Arctic
Herd in the Kuparuk Development Area, Alaska, during calving in 1979–81,
1982–86, and 1987–90. Each transect segment was 10.4 km
2
, or 0.9% of the
1150 km
2
surveyed. Only those segments with more than 0.9% of the total
caribou observed are shown. Gradations in line spacing depict caribou densities
as multiples of the base density derived from that percentage: wide spacing =
less than 3 × base; narrow spacing = 3–5 × base; solid = more than 5 × base
(Smith and Cameron, 1992; reprinted with permission).
FIG. 5. Histogram shows decline in abundance of calving caribou from the
Central Arctic Herd west of the Milne Point road system, Alaska, 1979–87
(Spearman’s Rank, p < 0.02). Abundance is expressed as a percentage of the
total numbers of caribou north of the Spine Road (see Fig. 1), shown in the line
graph below (Cameron et al., 1992b; reprinted with permission from Arctic).

ARCTIC CARIBOU AND PETROLEUM DEVELOPMENT • 5
(1973), and White et al. (1975) during the 1970s. Both
caribou abundance within the main industrial complex and
east-west caribou movements through that area were sig-
nificantly lower (p < 0.001) than in other areas occupied by
caribou along the Arctic coast. Conservative calculations
yielded an estimated 78% decrease in use by caribou and
a 90% decrease in their east-west movements (Cameron et
al., 1995), changes apparently in response to intensive
development of that region over the past three decades.
However, the occurrence of caribou that do use the com-
plex during summer is reportedly unrelated to distance
from infrastructure (Cronin et al., 1998).
Body Condition and Reproductive Performance
Reproductive success of caribou is highly correlated
with nutritional status. The probability of producing a calf
varies directly with both body weight and body fat content
of sexually mature females during the previous autumn
(Cameron et al., 1993, 2000; Cameron and Ver Hoef,
1994; Gerhart et al., 1997). In contrast, calving date and
perinatal survival are more closely related to maternal
weight shortly after parturition (i.e., estimated prepartum
body weight minus weight of fetal tissues) (Fig. 8). Thus,
the likelihood of conceiving is probably determined by
body condition at breeding, whereas parturition date and
calf survival may reflect maternal condition during late
gestation.
In theory, these relationships link the nutritional conse-
quences of changes in distribution to the reproductive
success of caribou of the CAH. West of the Sagavanirktok
River, caribou had reduced access to preferred foraging
habitats near roads (Nellemann and Cameron, 1996) and
FIG. 6. Relationship between mean (SE) density of calving caribou from the
Central Arctic Herd and road density within preferred rugged terrain, Kuparuk
Development Area, Alaska, 1987–92. Different letters indicate a significant
difference (p < 0.05) (Nellemann and Cameron, 1998; reprinted with permission
from the Canadian Journal of Zoology).
FIG. 7. Shifts in concentrated caribou calving areas of the Central Arctic Herd
between the Colville and Canning rivers (note oil field infrastructure, Fig. 1),
Alaska, 1980–95 (adapted from Wolfe, 2000: Fig. 3).

6 • R.D. CAMERON et al.
FIG. 8. Logistic regressions of parturition rate, incidence of early calving (on
or before 7 June), and perinatal calf survival (> two days postpartum) on autumn
and summer body weights of female caribou, Central Arctic Herd, Alaska,
1987–91. Solid lines are significant at p < 0.05. The empirical percentages are
shown at arbitrary 10 kg intervals of body weight. Numbers in parentheses are
sample sizes. *The weight category 60–70 kg includes one female weighing
57 kg (Cameron et al., 1993; reprinted with permission from the Canadian
Journal of Zoology).
FIG. 9. Mean (SE) body weights of lactating (n = 23) and nonlactating (n = 23)
female caribou in summer (July) and autumn (October), Central Arctic Herd,
Alaska, 1988–91. *Difference is significant at p < 0.001 (Cameron and White,
1996).
FIG. 10. Distributions of observed autumn (October) body weights for lactating
and nonlactating female caribou, Central Arctic Herd, Alaska, 1988–91. The
associated parturition rates are integrated estimates derived from the logistic
model (Fig. 8) (Cameron and White, 1996).
shifted their concentrated calving area into habitats with
lower plant biomass (p < 0.001) (Wolfe, 2000). In contrast,
forage biomass remained constant (p = 0.23) within con-
centrated calving areas east of the Sagavanirktok River,
where no development was present (Wolfe, 2000). Re-
peated use of lower-quality calving habitats may reduce
forage intake by females to the west. Likewise, impaired
summer movements between insect-relief habitat and in-
land feeding areas could depress energy balance (Smith,
1996) and, hence, rates of weight gain.
Indeed, several data sets suggest reduced nutritional
status and fecundity of radio-collared females exposed to
oil development west of the Sagavanirktok River. Esti-
mates of July and October body weights, over-summer
weight gain, the incidence of two pregnancies in succes-
sive years, and perinatal calf survival all tended to be
lower for females to the west than for those under distur-
bance-free conditions to the east, although individual
differences were not significant at the 95% confidence
level (Cameron et al., 1992a). In a more recent analysis of
data for 1988– 94, however, the mean parturition rate of
females west of the Sagavanirktok River was 64% com-
pared with 83% for females to the east (p = 0.003, Table 1)
(Cameron, 1995). Corresponding frequencies of repro-
ductive pauses (Cameron, 1994; Cameron and Ver Hoef,
1994) were 36% to the west of the river (26 of 73 observa-
tions) and 19% to the east (12 of 64 observations) (p < 0.02,
t-test, ratio method), or approximately one pause every
three and five years, respectively (Cameron, 1995). With
the opening of the Badami production unit east of the
Sagavanirktok River in 1996, the undisturbed status of that
area was compromised, rendering further comparisons
problematic.
The key constraint on reproduction is lactation: it ex-
acts a substantial cost on summer weight gain, which in
turn influences the probability of conceiving that autumn.
During 1988–91, weights of all lactating CAH females
sampled averaged 9 kg less than those of nonlactating
females (Fig. 9), resulting in a projected 28% reduction in
parturition rate (Fig. 10). Lower parturition rates of

ARCTIC CARIBOU AND PETROLEUM DEVELOPMENT • 7
females west of the Sagavanirktok River during 1988–94
(Table 1) may reflect a failure to compensate for the
metabolic burden of milk production (i.e., through in-
creased forage intake or reduced energy expenditure). The
result is consistently poorer condition in autumn and,
hence, more frequent reproductive pauses, which contrib-
ute to a decline in calf production of the herd (Fig. 2).
Yet the degree to which lactation constrains weight gain
does vary. An increase in net calf production during 1996–
2000 (Fig. 2) suggests the prevalence of forage and insect
conditions that enhanced growth and fattening, despite the
demands of milk production and the presence of industrial
activity.
CONCLUSIONS
Anthropogenic effects on caribou must be identified and
assessed within the framework of a variable natural environ-
ment. Favorable foraging and insect conditions would attenu-
ate the consequences of disturbance-induced changes in the
quality of habitats occupied. Conversely, adverse conditions
would exacerbate those same types of consequences (e.g.,
NRC, 2003:114–115). Unless analyses are based on multi-
year observations of marked individuals and incorporate
comparative data on an undisturbed control or reference
group, conclusions will be equivocal at best. For example,
absent a valid baseline, net growth of the CAH (Fig. 2) is no
better evidence of compatibility with development than a net
decline would be evidence of a conflict.
The crucial consideration for the future of the CAH and
other Arctic caribou herds is whether changes in distribution
associated with surface development, by depressing repro-
duction or survival, will either retard an increase in herd size
or accelerate a decrease. Our data, in fact, indicate that
productivity can and will decline if the cumulative loss of
preferred habitat, when superimposed on natural forces, is
sufficient to compromise nutrition.
ACKNOWLEDGEMENTS
Base funding was provided by Federal Aid in Wildlife Restoration
and the Division of Wildlife Conservation, Alaska Department of
Fish and Game. Supplemental support was provided by the Alaska
Fish and Wildlife Research Center, U.S. Fish and Wildlife Service;
Division of Habitat and Division of Subsistence, Alaska Department
of Fish and Game; Institute of Arctic Biology, University of Alaska
Fairbanks; ARCO Alaska, Inc.; EXXON Co. U.S.A.; SOHIO
Petroleum Co.; CONOCO, Inc.; Continental Pipeline Co.; and the
Alaska Department of Transportation and Public Facilities.
For analytical advice and technical assistance, we thank M.M.
Billington, D.A. Borchert, K. Butters, G.M. Carroll, R.A. Caulfield,
J.R. Dau, R.A. DeLong, S.G. Fancy, R.K. Friedrich, K.L. Gerhart,
C.S. Gewin, H.N. Golden, R.G. Hunter, N. Ihlenfeldt, K. Jouppi,
E.A. Lenart, J.A.K. Maier, T.R. McCabe, L.A. McCarthy, L.M.
McManus, D.C. Miller, S. Pedersen, D.J. Reed, J.W. Schoen, M.D.
Smith, R.T. Shideler, P. Valkenburg, J.M. Ver Hoef, N.E. Walsh,
K.R. Whitten, J.F. Winters, and S.A. Wolfe. S.G. Fancy and two
anonymous reviewers offered helpful comments and suggestions.
An earlier version of this paper appeared as a section in a U.S.
Geological Survey technical report (Cameron et al., 2002).
We dedicate this review to the memory of Ronald M. Warbelow,
who died in 1995 after a long battle with cancer. Equally skilled at
the controls of a helicopter or a fixed-wing aircraft, Ron was
instrumental in the success of caribou capture and survey programs
in the late 1980s and early 1990s. His friendship and enthusiastic
participation will not be forgotten.
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1
Central Arctic Herd, west and east of the Sagavanirktok River,
2
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% Parturient (n)
Year West East
1988 72.7 (11) 100.0 (8)
1989 53.8 (13) 77.8 (9)
1990 83.3 (12) 100.0 (7)
1991 45.5 (11) 75.0 (12)
1992 72.7 (11) 75.0 (12)
1993 55.6 (9) 62.5 (8)
1994 66.7 (6) 87.5 (8)
Mean parturition rate, %
3
64.3
± 5.0 82.5 ± 5.3
1
All sexually mature.
2
Individual locations consistently west or east for 2–7 years
during the calving period.
3
t-test, paired comparisons, p = 0.003.

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