174 
Franklin Bluffs (approximately 53 km away) to 
the SE and S respectively (Fig. 1). This drainage 
area was approximately 2,842 square km (Table 
16). Thus, the study area was approximately 
18% of the total drainage. It was anticipated 
that counts for the study area might be extrap- 
olated to the drainage, and further, that on days 
of high insect harassment, the number of cari- 
bou observed moving to the coastal dunes 
should represent the total number in the drain- 
age. Hence, observations of 20, 50, and 100 
animals in the study area should yield estimates 
of respectively 110, 280, and 560 animals in the 
entire drainage. These latter values are similar to 
the numbers of animals moving to the coastal 
dunes on some days in 1972 and 1973 (Fig. 2). 
However, the estimate is very low compared 
with two peak values of 1,500 and 1,200 ani- 
mals observed in 1972 (Fig. 2). 
(e) Estimation of caribou biomass and herb- 
age intake in relation to seasonal primary pro- 
duction. From the size of the study area and 
that portion containing grazeable herbage (Table 
16), an estimate was made of caribou densities 
(Table 17). In 1972 a mean population of 155 
animals was at a density of 3.4 km2 animal-!; 
the effective density was 1.9 km2 vegetated area 
animal-!. The following year (1973), total and 
effective stocking density were respectively 9.7 
and 5.2 km2 animal-!. At a seasonal primary 
production of 50-70 g m-2 (mean 55 g m2), it 
can be calculated that during the respective 
summers of 1972 and 1973, approximately 0.16 
and 0.03% of the aboveground vascular 
production was ingested. If the animals noted in 
1972 and 1973 remained on the study site 
year-round, then approximately 1.1 and 0.2% of 
the respective seasonal vascular productions 
would be removed in the entire year. 
/n vitro digestibility of plant species consumed 
by caribou 
Table 18 shows a comparison of indices of 
dry matter digestibility of selected plant species 
collected 12-25 July, 1972 at Prudhoe Bay. For 
the micro-digestion /n vitro technique, rumen 
liquor was obtained by rumenotomy from tran- 
quilized caribou, from rumen fistulated reindeer 
grazing vegetation at Prudhoe Bay, and from 
reindeer given prepared forages. 
Table 17 
Prediction of herbage intake by caribou in relation to seasonal primary production. 
Herbage intake was calculated over a period of 52 days (21 June through 10 August). 
Parameter 1972 1973 
Study area (km?) 
a) total 532 532 
b) vegetated 288 288 
Population size (average July/August) 155 55 
Caribou density (No. km*2) 
a) total 0.29 (3.4) 0.10 (9.7) 
b) vegetated 0.54 (1.9) 0.19 (5.2) 
Seasonal primary production ~ 
Prudhoe Bay (kg km’) 55,000 55,000 
(range 50-70 g m2) 
Herbage intake (50 d study period) 
a) total (kg) 25,000 5,400 
b) per unit area (kg km?) 87 19 
c) percentage of above-ground production 0.16 0.03 
Value in parenthesis is caribou density expressed as km? caribou’!. 
“Calculated as peak above-ground, vascular live material. 
