ICES J. mar. Sci., 53: 61–72. 1996
Evidence of a decline in beluga, Delphinapterus leucas,
abundance off West Greenland
Mads Peter Heide-Jørgensen and Randall R. Reeves
Heide-Jørgensen, M. P. and Reeves, R. R. 1996. Evidence of a decline in beluga,
Delphinapterus leucas, abundance off West Greenland. – ICES J. mar. Sci., 53: 61–72.
Aerial surveys of belugas, or white whales, Delphinapterus leucas, were conducted off
West Greenland in March 1993 and 1994. These surveys were designed to permit
comparisons with similar surveys in 1981, 1982, and 1991. Differences in methods
between the surveys in the early 1980s and those in the 1990s should mean that the
1990s surveys were, if anything, more efficient than the 1980s surveys. Weighted linear
regressions of strip-census estimates of the relative abundance of belugas showed a
significant decline from 1981 to 1994. While annual variability in ice conditions and
other unknown factors may have had some local or small-scale effects on the
movements and distribution of belugas off West Greenland, it is unlikely that these
effects would account for the apparent decline in relative abundance. The most
reasonable conclusion is that the stock size has declined considerably during the past
13 years, perhaps by as much as 62%.
? 1996 International Council for the Exploration of the Sea
Key words: beluga, Delphinapterus cas, aerial survey, West Greenland.
Received 11 July 1994; accepted 16 May 1995.
M. P. Heide-Jørgensen: Marine Mammal Section, Greenland Fisheries Research
Institute, Tagensvej 135, DK-2200 Copenhagen N, Denmark. Randall R. Reeves: Okapi
Wildlife Associates, 27 Chandler Lane, Hudson, Quebec J0P 1H0, Canada.
Introduction
The distribution of belugas, or white whales,
Delphinapterus leucas, along the west coast of Greenland
has changed dramatically during the last 70–90 years. At
least some of this change can be attributed to overhunting. In the early 1900s, West Greenlanders abandoned
the traditional use of kayaks and began using motordriven boats to drive herds of belugas into shallow
bays or sounds, locking them inside with nets (HeideJørgensen, 1994). The demand for blubber to produce
oil and for whale skin to produce leather stimulated the
development of a commercial beluga fishery. Some of
the exploitation of belugas was organized by the Danish
administration in Greenland and some by local hunters
and fishermen who had received financial support from
the Danish government to buy vessels for cod fishing.
These vessels were also used for hunting belugas and
walruses, Odobenus rosmarus (Heide-Jørgensen, 1994;
Born et al., 1994).
The largest drive fisheries were in southwestern
Greenland at Nuuk (64)N) and Maniitsoq (65)30*N)
districts, were a cumulative total of more than 11 000
belugas were taken during 1906–22 and 1915–29, respectively (Heide-Jørgensen, 1994). This intensive killing
1054–3139/96/010061+12 $12.00/0
resulted in the virtual disappearance of belugas from
areas south of 66)N. Large catches continued to be made
periodically during and after the 1930s in districts farther north; for example a drive fishery was conducted at
Upernavik (72)30*N) from 1927–51. The largest catches
in recent years have been taken at progressively more
northern settlements (Heide-Jørgensen, 1994).
Belugas that winter off West Greenland are believed
to summer mainly in the Canadian High Arctic. A
survey in 1981 produced an estimate of 12 450 belugas
(95% CI: 6300–18 600) for the summering grounds in
Canada (Smith et al., 1985). A population of this size
would not have been able to sustain the combined
catches in Canada and Greenland during the 1980s and
early 1990s (Heide-Jørgensen, 1994). Thus, either the
beluga stock has been overexploited since the early
1980s or the population estimate from 1981 was an
underestimate, or possibly both. Results of aerial surveys strongly suggested that the number of belugas
wintering along the West Greenland coast had declined
between 1981 and 1991 (Heide-Jørgensen et al., 1993).
The statistical power of the survey results, through 1991,
was sufficient to determine only that the decline was
significant at a probability level of 87% (á=0.13). While
this level falls short of the traditional 95% (á=0.05)
? 1996 International Council for the Exploration of the Sea
62
M. P. Heide-Jørgensen and R. R. Reeves
required for statistical significance, it should be noted
that, in other contexts involving the management of
marine resource exploitation, lower levels of significance
have been considered acceptable for decision-making
(Peterman, 1990; Forney et al., 1991; Richard et al.,
1994).
Uncertainty about the status of the Baffin Bay stock
of belugas, especially in view of the continued large
catches in Greenland, suggested the need for close
population monitoring with standardized surveys. This
paper presents results of aerial surveys conducted off
West Greenland in 1993 and 1994, using similar effort,
timing, and design as those of previous surveys.
Comparisons are made mainly with the 1981, 1982, and
1991 surveys to evaluate population trends.
Materials and methods
McLaren and Davis (1983) and Heide-Jørgensen et al.
(1993) documented the winter distribution of belugas off
West Greenland on the basis of surveys conducted in
1981, 1982, 1990, and 1991. Five strata were constructed
for use in comparing beluga abundance between and
among years. Although data from the 1990 survey were
included in the study by Heide-Jørgensen et al. (1993),
we have excluded them from the present study because
of the difference in timing. The 1990 survey began 3–4
weeks later in the year than the other five surveys.
Survey design
Systematic aerial surveys of marine mammals were
conducted off West Greenland during 16–22 March
1993 and 11–24 March 1994. The survey procedures
were essentially identical to those used in 1990 and 1991
(see Heide-Jørgensen et al., 1993 for details). The same
aircraft was flown at a similar target altitude (213 m)
and speed (1993: mean=163 km/h, 95% CI: 157–168,
1994: mean=171 km/h, 95% CI: 169–174). Altitude
measurements from a radar altimeter were recorded at
30-s intervals for comparison with the readings from the
aircraft’s barometric altimeter. This procedure confirmed that the target altitude was maintained with
reasonable consistency throughout the surveys. Four
experienced observers participated in the 1993 and 1994
surveys: Heide-Jørgensen and J. Teilmann in 1993;
Heide-Jørgensen, Reeves, and J. Jensen in 1994. The two
observers on each flight sat in the rear seats and
recorded perpendicular angle and pod size for each
sighting. Ice conditions and visibility were noted at
2-min intervals by the pilot. All data were recorded
initially on independent tape recorders activated by the
observer, who pressed a hand-held switch and spoke
into the microphone of his headset. Activation of the
tape recorder prompted a synchronized time signal
which was fed on to the tape from a computer. All data
were transcribed from the tape recorders on to standard
forms at the end of each survey day.
East–west transects were flown in all strata (Fig. 1).
The highest coverage was achieved, both years, in strata
3–5, where transects separated by 5 nm (9.3 km) were
flown twice, with each replicate separated by approximately one week. The two northernmost strata were
given less coverage because of the severe ice conditions
and expected low density of belugas. Transects in these
strata were separated by 10 nm (18.5 km) in 1993 and
were flown only once in 1994.
In 1993, a few transects were allocated to areas south
and north of the main strata (Fig. 1), and the open water
in the northern part of Vaigat was surveyed for walruses
but with no sightings of belugas. In 1994, reports of
belugas being sighted off Nuuk (Fig. 2) in early January
and Paamiut (Fig. 2) somewhat later in the winter were
provided through the KNAPK (Greenland Fishermen
and Hunters Association). In addition, several people
reported a large aggregation of perhaps 1000 belugas
moving south off Maniitsoq (Fig. 2) on 12 December
1993 and again in early January 1994 (GFRI, unpubl.).
The possibility that appreciable numbers of belugas
could be present south of the study area prompted us to
fly a reconnaissance survey over coastal waters between
62)30*N and 66)00*N on 16 March 1994 (Fig. 2). Having
established that belugas were present during the survey
period as far south as 65)40*N, we created Stratum 6 to
extend our systematic coverage south to that latitude.
East–west transects at 10 nm intervals in Stratum 6 were
flown once during the last day of our 1994 survey.
Statistical analysis
For the comparisons with surveys in 1981, 1982, and
1991, strip-census estimation, with a pre-defined strip
width of 700 m on either side of the transect, was applied
to the 1993 and 1994 data (see Heide-Jørgensen et al.,
1993). Estimates were computed following the ‘‘ratio
method’’ (Cochran, 1977) where the variance of the
abundance was estimated as the empirical variance of
bootstrapped values resampled 1500 times within each
stratum with each transect line as the bootstrap unit.
We fitted a straight line through the abundance
estimates from 1981–1994 by using weighted least
squares estimation (WLSQ) with weights equal to the
inverse of the estimated variances. Thereafter, the
parameters of the weighted least squares line were
adjusted to fit an index value of 100 in 1981.
To determine the quantiles of the intercept and the
slope a value from the bootstrapped values for each
year from 1981–1994 was drawn at random. A new
WLSQ was performed on the five randomly drawn
values. This procedure was repeated 10 000 times, thus
providing a sample of 10 000 of the estimator values of
the slope and the intercept. From these samples 2.5%
0
60°W
11 to 20
6 to 10
1 to 5
16–22 March
1993
21 to 50
50
5
4
3
0
20
2
1
55°W
25 50
50°W 60°W
Kilometers
0
0
Store
Hellefiske
Banke
11 to 20
6 to 10
1 to 5
11–24 March
1994
21 to 50
50
(b)
6
5
4
3
0 2
20
1
55°W
Disko
Vaigat
25 50
50°W
Kilometers
0
Disko
Bay
Figure 1. The study area off West Greenland with the six strata (rectangles bounded by broken lines), transects flown (solid lines) and beluga sightings (on and off transect), (a) 16–23
March 1993 and (b) 11–24 March 1994.
66°N
68°N
70°N
(a)
Decline in West Greenland beluga
63
64
M. P. Heide-Jørgensen and R. R. Reeves
Maniitsoq
66°N
Sightings of belugas
16 March 1994
13 individuals
Nuuk
64°N
0
25 50
Kilometers
Paamiut
62°N
56°W
52°W
48°W
Figure 2. Map of reconnaissance flight along West Greenland on 16 March 1994.
and 97.5% empirical quantiles were determined, thus
giving 95% confidence intervals for the intercept and the
slope.
To construct a confidence band for the weighted
linear regression, 200 equally spaced values between
1981 and 1994 were chosen. For each of these values the
10 000 estimates of slopes and intercepts were used to
calculate the corresponding abundance estimate. Again,
2.5% and 97.5% quantiles were estimated empirically to
derive the 95% confidence bands for the weighted linear
regression.
Although the 1991 and 1993–94 data were collected in
such a way that they could be used for line-transect
estimation, the 1981–82 data were not. We recognized,
however, that effective search half-widths (ESW) could
provide a basis for comparing the relative efficiencies of
the 1991, 1993, and 1994 surveys. To estimate the ESW
for each year, several models (Fourier series, negative
exponential, hazard-rate and half-normal) were fitted to
the perpendicular distances of pods and belugas. The
1-term cosine Fourier series (the linear combination of a
series of cosine functions),
f(x)=1/W+a cos(ðx/W)
where a is the parameter estimated from the data, x
are the distances and W the half-width of the transect
(e.g. Burnham et al., 1980; Buckland et al., 1993),
outperformed the other models and provided good fits
to each data set. The pooled frequency distribution of
distances for 1991, 1993, and 1994 was truncated at
W=1000 m. Maximum likelihood estimation of the
ESW and its associated empirical variance was done
using the computer program ‘‘Distance’’ (Laake et al.,
1993). When evaluated at zero, f(x) is f(0)=1/W+a.
Decline in West Greenland beluga
Results
1.4
Homogeneity of observers
1.2
1991: ESW=520 m, CV=0.044, n=773
1.0
0.8
0.6
0.4
0.2
Probability of detection
The sighting rates of the two observers in 1993 did not
differ significantly (paired t-test: p=0.64). Their respective mean pod size estimates were 2.28 and 3.06, but if
one extreme observation of a pod of 26 belugas is
excluded, the latter figure is reduced to 2.57. Even when
including the extreme observation of 26 belugas, the
difference in mean pod size was not statistically significant (Mann-Whitney: p=0.97). Hence, these two observers can be considered equally efficient. For
comparing 1993 results with those of 1991, observer
heterogeneity is of no importance as the same observers
were used for both sets of surveys.
Pairwise comparisons among the three observers in
1994, one of whom had been involved in the 1990, 1991,
and 1993 surveys, revealed no significant differences in
either mean pod size (Kruskal Wallis: p=0.1168; mean
of pod size estimates: 2.691, s.e. 0.393; 2.197, s.e. 0.27;
2.952, s.e. 0.407) or sighting rate (t-test, p-values of
0.0859, 0.2358, and 0.8443).
The observers used in the 1981–82 surveys were all
different from those used in the 1990–94 surveys, so no
direct comparisons were possible. However, the observers in the 1981–82 surveys were more heterogeneous
than those in the 1990s surveys (see Heide-Jørgensen
et al., 1993).
65
0.0
1.2
1993: ESW=500 m, CV=0.018, n=110
1.0
0.8
0.6
0.4
0.2
0.0
1.2
1994: ESW=515 m, CV=0.027, n=173
1.0
0.8
0.6
0.4
0.2
0
100 200 300 400 500 600 700 800 900 1000
Perpendicular distance from trackline (m)
Figure 3. Perpendicular distances to sightings of belugas in
1991, 1993, and 1994. Sightings more than 1000 m from the
trackline were excluded from analyses. Data have been fitted by
the Fourier series model with 1 cosine adjustment.
Efficiency of the surveys
Although timing and survey design were almost identical
in 1991, 1993, and 1994 and the same observers were
used in 1991 and 1993, the surveys still may not have
been equally efficient. Differences in efficiency could
have been caused by variations in sighting conditions,
use of different observers or different behaviour of the
whales. There is no straightforward way to measure the
efficiency of a given survey. However, one useful parameter is the ESW, which provides an indication of some of
the detection variability. We restricted the ESW to
having a similar functional form for all the surveys. The
distribution of sighting distances shows a monotonic
decrease with distance from trackline, with a shoulder
for the first 100 m (Fig. 3). The estimated ESW was
similar for 1991 (ESW=520 m, CV=0.044), 1993
(ESW=500 m, CV=0.018) and 1994 (ESW=515 m,
CV=0.027). Thus, in terms of ESW, the three surveys
can be assumed to have been similarly efficient.
Ice conditions and distribution of belugas in 1993
The winter of 1992–93 was among the coldest ever
recorded in West Greenland, so severe ice conditions
were expected on the beluga wintering grounds. How-
ever, several recent gales had caused considerable
movement of the ice, which was riven with large leads,
cracks, and open water areas by the time the surveys
began. Many of the leads and cracks became partially
or completely refrozen during the survey period, but
substantial open water persisted in areas south of 68)N
(Fig. 4). Along the east–west transect at 68)10*N at the
northern edge of Store Hellefiske Banke numerous
icebergs were grounded or frozen into the sea ice.
Fast ice prevailed in the area north of 68)N, and
Disko Bay, Vaigat, and the area west of Disko were
covered by fast ice, with only a few small areas of
open water. Ice conditions, overall, appeared more
similar to those in 1982 and 1991 than to those in 1981
and 1990 (cf. Heide-Jørgensen et al., 1993, also see Fig.
5, below).
Searches for belugas west of Disko Island north of
Stratum 1 revealed no evidence of their presence north
to 70)20*N. The open-water area in the northernmost
part of Vaigat (Fig. 1) was also searched for belugas,
without success. Strata 1 and 2 were both dominated by
fast ice and close pack ice, with only occasional small
leads and cracks in which narwhals, Monodon
monoceros, were sometimes sighted. The general absence
66
M. P. Heide-Jørgensen and R. R. Reeves
Figure 4. NOAA satellite images showing approximately average ice conditions in southern Baffin Bay and central Davis Strait
during the surveys on (a) 23 March 1993 and (b) 19 March 1994. Reproduced with permission from the Danish Meteorological
Institute.
of open water made these two strata largely unsuitable
for belugas; hence, survey coverage of them was
reduced.
No belugas were observed in Stratum 1. The northernmost sighting was in Stratum 2 at 69)10*N, 54)16*W,
where several pods were observed in a narrow lead.
However, the one primary sighting was made at a
distance of 2400 m from the trackline, thus beyond the
truncation distance. No other evidence of belugas in
Stratum 2 was obtained.
The highest numbers of belugas were found in
Stratum 4, but the two neighbouring strata (3 and 5)
also had substantial numbers (Fig. 1 and Table 1).
Comparison of the results of replicate coverage in these
three strata revealed no significant differences. Although
mean pod size for the first set of replicates in Stratum 4
was considerably higher than that for the second
(Table 1), the difference in relative abundance was not
significant.
Ice conditions and distribution of belugas in 1994
Although the winter of 1993–94 was warmer than that
of 1992–93, sea-ice conditions off West Greenland were
broadly similar (Figs 4, 5). During 18–20 March,
between the first and second set of 1994 replicates in
Strata 3–5, strong winds from the north-east drove the
pack ice away from the coast and caused much of it to
break up. This change in ice conditions may help to
explain the marked decline in both the sighting rate
and the abundance estimate between the first and
second replicates in Stratum 5 (Table 1). The suggestion is that the less severe ice conditions in the central
and northern parts of the study area allowed the
animals to begin moving northwards after 18 March.
The concomitant increases in the abundance estimate and average pod size (but not sighting rate) in
Stratum 4 (Table 1) appear to be consistent with this
interpretation.
Decline in West Greenland beluga
67
100
Percentage of surveyed area
80
60
40
20
0
1981
1982
1991
Year
1993
1994
Figure 5. Ice conditions encountered during surveys of belugas off West Greenland, 1981–94. In 1982, 1991, 1993, and 1994, the
ice coverage was recorded, in tenths, for each 2-min segment of the transects. In 1981, each 2-min segment was assigned to one of
five categories of percent ice coverage. =9–10; =5–8; =1–5; =0.
A few pods of belugas, including one large group of
about 30 animals (in two pods), were observed in the
cracks of open water at the mouth of Disko Bay and off
the west coast of Disko to as far north as 69)30*N (Fig.
1). Their presence in Stratum 1 and the northern part of
Stratum 2 suggests that some belugas could have been
north of our study area during the 1994 survey. We were
unable to sample north of Stratum 1 but, judging by the
similarity in ice conditions between 1994 and 1993, there
is no reason to believe that large numbers of belugas
would have been found north of 69)30*N in 1994.
The reconnaissance survey south to 62)30*N on 16
March provided good coverage, under excellent conditions, of the shallow nearshore waters where belugas
might be expected to occur (cf. Heide-Jørgensen et al.,
1993). There was surprisingly little open water but
the extensive newly-formed ice had many leads and
cracks. Three pods, totalling 13 belugas, were seen
in a lead at 65)40*N, 53)58*W (Fig. 2). The systematic
survey of Stratum 6 on 24 March was done in excellent
sighting conditions, but belugas were seen only on the
northernmost transects (Fig. 1).
conditions during the survey period. The categories of
ice conditions used in 1981 were different from those
applied in later years. In addition, different people
collected the ice data in the 1980s and in the 1990s.
While we would expect the classifications of open water
and 9/10–10/10 ice coverage to be reasonably consistent
regardless of who collected the data, the data for other
classifications could be biased by observer variability.
Nevertheless, it seems fair to conclude that there was
probably the greatest amount of open water in 1981 (up
to 11%) while the least was in 1982 (Fig. 5). In the 1990s,
approximately 5% of the study area had open water,
while the percentage with fast ice varied between
20–33%, compared with 4% in 1982. One could say,
based on these data, that 1981 and 1982 represented two
extremes in ice conditions (‘‘open’’ vs. ‘‘closed’’, respectively) and that the three years in the 1990s were all
intermediate between these two extremes. Alternatively,
one might emphasise the relatively large amount of fast
ice prevailing in the 1990s compared with the 1980s. Its
effect could be either to force the whales into more
concentrated clumps or to drive them out of the study
area.
Annual variation in ice conditions
In all years, ice conditions have been recorded in 2-min
segments on each transect. As the transects sample the
study area systematically, the data on ice coverage,
collected in 2-min segments, can be regarded as providing a representative and consistent description of ice
Changes in relative abundance of belugas
When results from the 1993 and 1994 surveys are added
to the trend analysis, it becomes evident that the decline
detected from 1981–82 to 1991 (Heide-Jørgensen et al.,
1993) is even more pronounced (Fig. 6). The resulting
68
M. P. Heide-Jørgensen and R. R. Reeves
Table 1. Sighting rates, mean pod sizes and estimates of relative abundance for strip-census surveys off West Greenland, 1991,
1993, and 1994. Stratum replicates (numbered 1 and 2) were flown approximately five days apart. Coefficients of variation
calculated as standard error in proportion to the mean are indicated in parentheses.
Effort
(L, km)
Sightings
(n)
Sighting
rate
(n/L)
Stratum
Replicate
(a) 1991
1
2
3
4
5
Total
1
1
1
1
1
137
951
747
595
440
2868
6
10
36
3
19
74
1
1
1
2
111
485
735
570
1305
619
525
1144
442
417
859
3222
0
0
27
19
46
10
13
23
20
14
34
103
0
0
0.0367 (0.49)
0.0333 (0.47)
0.0353 (0.33)
0.0162 (0.45)
0.0248 (0.42)
0.0201 (0.30)
0.0453 (0.37)
0.0336 (0.32)
0.0396 (0.24)
0.0329 (0.18)
157
962
849
808
1657
565
320
885
449
444
893
422
4554
2
3
43
42
85
9
2
11
33
14
47
5
148
0.0152
0.0031
0.0510
0.0526
0.0518
0.0159
0.0063
0.0124
0.0735
0.0315
0.0526
0.0118
0.0325
(b) 1993
1
2
3
3
Sum 3
4
4
Sum 4
5
5
Sum 5
Total
(c) 1994
1
2
3
3
Sum 3
4
4
Sum 4
5
5
Sum 5
6
Total (1–5)
1
2
1
2
1
1
1
2
1
2
1
2
1
95% confidence intervals for 1993 and 1994 do not
overlap those for 1981 and 1982. Weighted linear regression through each survey suggests that the population
may have declined by as much as 62% (95% CI: 38–75%)
between 1981 and 1994. This corresponds to an annual
decline of 4.7% (95% CI: 2.1–7.2%) evaluated in 1981.
Weighted linear regression of the log-transformed
index values showed an annual decline of 7.5% (95%
CI: 3.8–10.7%).
If the effort and sightings in Stratum 6 in 1982 (see
Heide-Jørgensen et al., 1993) and 1994 are incorporated
into the abundance estimation, the apparent decline in
index values from 1982–1994 is 47%. Furthermore, the
bootstrapped quantiles (2.5–97.5%) of the 1982 abundance estimate (95% CI: 1540–3117) do not overlap
those of the 1994 estimate (95% CI: 775–1532) including
the Stratum 6 data.
0.0435
0.0106
0.0482
0.0050
0.0438
0.0258
(0.76)
(0.49)
(0.35)
(0.69)
(0.39)
(0.24)
(0.55)
(0.71)
(0.33)
(0.32)
(0.22)
(0.49)
(0.55)
(0.42)
(0.43)
(0.32)
(0.33)
(0.90)
(0.18)
Mean
pod
size
2.667
2.900
3.222
3.667
3.263
3.162
(0.21)
(0.31)
(0.15)
(0.48)
(0.45)
(0.15)
—
—
2.111 (0.14)
1.842 (0.21)
2.000 (0.12)
5.700 (0.43)
4.154 (0.29)
4.826 (0.26)
2.150 (0.16)
2.142 (0.29)
2.147 (0.15)
2.954 (0.13)
1.500
1.667
2.744
2.048
2.400
3.000
11.000
4.454
2.303
2.714
2.426
1.200
2.534
(0.33)
(0.19)
(0.15)
(0.12)
(0.10)
(0.31)
(0.27)
(0.29)
(0.16)
(0.50)
(0.20)
(0.17)
(0.23)
Abundance
estimate
104
189
755
69
355
1471
(0.75)
(0.74)
(0.35)
(0.86)
(0.46)
(0.26)
0
0
337 (0.48)
238 (0.42)
297 (0.35)
396 (0.65)
381 (0.40)
389 (0.37)
245 (0.58)
181 (0.43)
214 (0.38)
900 (0.21)
6
32
652
475
566
184
256
209
426
102
265
85
1078
(0.73)
(0.64)
(0.31)
(0.34)
(0.23)
(0.52)
(0.49)
(0.37)
(0.41)
(0.29)
(0.40)
(0.86)
(0.18)
Pod characteristics and age classification
The trend of decreasing pod size reflected in the data
from 1981–82 and 1990–91 (Heide-Jørgensen et al.,
1993) is also evident from the 1993–94 data (Fig. 7). The
decline in strip-census abundance estimates, across
years, reflects the reduction in pod sizes from a mean of
4.9 (CV=0.10) in 1981–82 to 3.1 (CV=0.15) in 1991, 2.7
(CV=0.13) in 1993, and 2.6 (CV=0.09) in 1994. The
common mean pod size for 1991–94 (mean=2.7,
CV=0.07) was significantly (p<0.05) lower than the
mean pod size for 1981–82. The pod size distributions
from within the periods of 1981–82 and 1991–94 did not
differ significantly (Kolmogorov-Smirnov: p>0.05) but,
between the periods, all pod size distributions differed
significantly (p<0.05). While some of the apparent
trends may be due to the fact that different observers
Decline in West Greenland beluga
Index of relative abundance
225
200
175
150
125
100
75
50
25
0
1980 1982 1984 1986 1988 1990 1992 1994
Year
Figure 6. Weighted linear regression of strip-census estimates of
relative abundance of belugas in the surveyed area off West
Greenland for 1981, 1982, 1991, 1993, and 1994. To avoid
giving the impression that these estimates are of the entire
population abundance, they are shown as index-values on a
scale from 1 to 100. Vertical lines indicate 95% confidence limits
around each annual estimate whereas the bands around the line
indicate the 95% confidence band of the regression.
classified pods differently or had different rounding
tendencies, the most compelling feature of the data is the
decline in percentage of large pods (10+ individuals), a
69
category that should be fairly robust to observational
and methodological variability.
In 1993, 56% of classified individuals were white
(including mothers accompanied by ‘‘calves’’), 36%
were grey (not including ‘‘calves’’) and 8% were
‘‘calves’’. In 1994, the respective percentages were 73%,
18%, and 9%. The similarity of the 1993 percentages to
the 1990 and 1991 percentages (see Heide-Jørgensen
et al., 1993, Table 6), and their dissimilarity from the
1994 percentages, can be interpreted as being due to
observer bias of some kind. Whereas the two observers
used in the 1990, 1991, and 1993 surveys apparently
classified whales consistently, the two new observers
used in 1994 may have been more likely to note the
colour of white animals than that of grey animals. It
should be noted that we used only those sightings for
which all animals in the pod were colour-classified to
calculate percentages. This meant that if, for example,
the observer noted that several animals in a pod were
grey but failed to specify the colours of the other pod
members, the entire pod was excluded from the calculations. Of 55 whales excluded on this basis in 1994, 11
(20%) were grey and 6 (11%) were ‘‘calves’’.
The percentages of white and grey animals recorded in
the aerial surveys differed greatly from the composition
45
50
40
45
35
40
30
35
25
30
20
25
15
20
10
15
5
10
Percentage of total sightings
Percentage of total sightings
50
5
0
1
2
3
4
Pod-
size
5
6
class
es
7
8
9
10+
0
1981
1982
1991
ar
Ye
1993
1994
Figure 7. Changes in frequency distribution of beluga pod sizes from 1981–94. The pod sizes are shown in 10 different classes. Pods
of ten or more belugas are pooled in class 10+.
70
M. P. Heide-Jørgensen and R. R. Reeves
The pooled data on whale headings from 1993 and 1994
(all strata combined) showed no tendency for directional
movement and were essentially uniform when assigned
to eight categories (p>0.05; Kuiper test, see Batschelet,
1981). The same percentage of sightings (36%) had
southbound as northbound headings. It should be
noted, however, that we did not exclude from the sample
of headings those in which the whales were milling,
feeding, or resting. The orientations (headings) of such
whales would be essentially random and would probably
indicate little or nothing about directional tendencies in
the population.
this reconnaissance survey, together with the few other
sightings south of Stratum 5 in 1994, also demonstrated
that the five original strata did not quite extend to the
southern limit of the March distribution.
Simultaneously with the 1993 West Greenland survey,
an aerial survey was conducted of the North Water, a
flaw-lead system in northern Baffin Bay that is the only
other known wintering area of the Baffin Bay stock of
belugas (Richard et al., 1993). Approximately 500
belugas were observed during reconnaissance flights
over the limited leads and cracks that were present in
the North Water in 1993. This total is similar to the
numbers documented during surveys of the North Water
in 1978 and 1979 (Finley and Renaud, 1980). It can
therefore be concluded that fewer belugas probably
overwinter in the North Water than off the coast of
central West Greenland and that no obvious increase in
numbers wintering in the North Water took place
between 1978–79 and 1993.
Discussion
Trends in the beluga population
Overall distribution and relative abundance
The limited time-series of surveys of wintering belugas
off West Greenland unambiguously demonstrates that
relative abundance has declined between the early 1980s
and early 1990s. It is not certain whether this decline was
also experienced at the same rate in the entire population (Baffin Bay stock) but it seems plausible that it
would be, as no major shift in distribution or increase in
relative abundance in other potential wintering areas has
been detected. Of the likely causes of the decline,
hunting is probably the single most important one.
A question of both theoretical and practical interest is
how large, in absolute terms, the Baffin Bay stock of
belugas might be. As has been repeatedly emphasised,
the West Greenland aerial surveys in winter account for
an unknown fraction of the entire stock and thus can
only provide an index, rather than an estimate, of the
population’s absolute size (cf. Heide-Jørgensen et al.,
1993). Abundance estimates from aerial survey are
negatively biased because only animals at the surface, or
within a few metres of it, are sampled. Correction
factors of 1.15–1.75 have been used or proposed for
photographic census surveys of belugas (Kingsley,
1993). Because of differences in ‘‘efficiency’’ between
photographic images and visual searches of the water
surface, we are reluctant to use the same correction
factors for both. However, even if the highest of these
correction factors (1.75) were applied to the upper
confidence limit of the highest strip-census estimate of
belugas off West Greenland in March (about 9625 in
1981; see Heide-Jørgensen et al., 1993, Table 4), the
population estimate would still be too small for the
catches between 1981 and 1992 to have been sustainable
(Heide-Jørgensen, 1994). The lower end of a 1981
estimate of beluga abundance of 12 450 (95% CI:
of catches at Upernavik, where the majority of whales
taken by driving were less than 5 years old (HeideJørgensen and Teilmann, 1994) and would not yet have
turned white.
Whale headings
Judging from the satellite images and the ice conditions
observed during the aerial surveys, it seems unlikely that
appreciable numbers of belugas would have been present
in eastern Baffin Bay north of 70)N during the survey
periods in 1991, 1993, and 1994. Catches in Disko Bay
did not begin in 1993 before 10 April or, in 1994, before
mid-April (Heide-Jørgensen, unpubl.), fully two weeks
after the surveys ended in both years. The searches in
areas north of Stratum 1 in 1993 revealed no belugas
and it can be assumed that few, if any, had started their
northward migration before or during the survey.
The situation was somewhat different in 1994 as we
had more sightings in Stratum 2 and several in Stratum
1. Most of the belugas seen in these strata, including the
large group of 30 in Stratum 1, appeared to be heading
north. Although these observations suggest that the
surveyed population was not ‘‘closed’’ to the north, it
still seems reasonable to assume that the proportion of
belugas outside the surveyed area was not larger in
either 1993 or 1994 than it was in the previous years with
surveys.
No belugas had been seen south of 66)30*N in
previous March surveys (Heide-Jørgensen et al., 1993).
One animal was seen south of this latitude in 1993. Thus,
we cannot exclude the possibility that some additional
animals were present in areas south of Stratum 5 in
1993. Results of the reconnaissance survey south to
62)30*N in 1994 generally confirmed the observations
of previous investigators that the present-day winter
(March) distribution of belugas off West Greenland is
primarily north of 66)30*N (Heide-Jørgensen et al.,
1993; Heide-Jørgensen, 1994). However, the results of
Decline in West Greenland beluga
6300–18 600) on the Canadian summering grounds (with
no corrections for submerged animals; Smith et al.,
1985) is within the corrected estimate derived from the
West Greenland surveys in March 1981.
Variability
The calculated variance in estimates of density and
abundance accounts for the variability intrinsic to distance sampling, but it does not address other elements of
variability which might confound our results. Ice conditions undoubtedly affect the distribution and movements
of the whales, and possibly also the size of aggregations
(pod sizes). They may also affect the detection probabilities and the abilities of observers to judge pod sizes.
Significant changes in ice conditions off West Greenland
in March can occur on time scales of hours, days, or
weeks. The within-survey effects of such changes are
virtually intractable. While we can make general comparisons of ice conditions between surveys, for example
by examining satellite images (Fig. 4) and tediously
plotting the data collected during the surveys on ice
types and percent coverage (Fig. 5), we can only speculate about the ways that different ice conditions might
affect the actual behavior of the animals, and our
perceptions of their behavior, during the surveys.
One approach to investigating the nature and extent
of within-survey variability is by making pairwise comparisons between transect replicates. However, the
results of such an analysis, when applied to the 1993 and
1994 data, revealed no consistent or unambiguous basis
for making inferences. As discussed in the Results, it is
possible to account for the most obvious differences
between replicates by assuming that the whales made
only short-range movements between strata in response
to fluctuating ice conditions. There is no evidence that
appreciable numbers of whales moved out of or into the
study area during the survey periods.
The basic migratory schedule of belugas is quite
consistent and seems to be governed primarily by
photoperiod rather than by other physical or biological
factors, including sea-ice conditions. They migrate
rapidly away from the summering grounds in the
Canadian High Arctic in early September as day length
shortens (Davis and Finley, 1979; Smith and Martin,
1994). Smith et al. (1994) reported the first arrival of
belugas at Cunningham Inlet as occurring within a
2-week interval (8–21 July) in seven seasons with
data; their departure was within a similar interval
(3–16 August) in five seasons with data. The timing
of belugas’ arrival in Northwest Greenland in late
September or early October is remarkably consistent
(Heide-Jørgensen, 1994). The spring northward migration in Baffin Bay coincides with the dramatic increase in
daylight.
71
Trends in catch and effort in Greenland
The decline in relative abundance of belugas off West
Greenland should have reduced their availability to
Greenlandic hunters. Such reduced availability would be
reflected by trends in the catch rate unless any trend
were masked by changes in hunting effort or technology.
Unfortunately, none of these parameters (catch rate,
hunting effort, hunting methods) has been adequately
monitored. Catch statistics for North and West
Greenland became decreasingly reliable during the 1980s
and were no longer being kept by the end of that decade
(Heide-Jørgensen, 1994). Belugas are captured in
Greenland by a variety of techniques and catches are
often made either opportunistically or during multispecies harvesting operations. Little attention has been
given to the problem of documenting catch effort.
Conclusions
The variance estimates in our survey results obviously
do not account for all of the uncertainty that is intrinsic
to the index values. A variable proportion of the whale
population may winter outside the survey strata (e.g. in
the North Water) from one year to the next, and ice
conditions can affect survey efficiency (i.e. cause a positive or negative bias on numbers of sightings and sizes
of pods, see above). Nevertheless, the results of the
1993 and 1994 surveys reinforce the conclusion of
Heide-Jørgensen et al.. (1993) that the wintering population off West Greenland has been ‘‘much reduced’’
since the early 1980s.
Whatever the cause or causes of the apparent decline
in relative abundance off West Greenland, and however
this decline may relate to the entire Baffin Bay stock,
there is reason for concern about the observed trend.
The most likely explanation of the decline is that the
annual removals from the population by hunting, particularly in West Greenland, have exceeded the replacement yield. If this explanation is correct, then the only
way to achieve stasis in the population is by adjusting
the removal rate downwards to where it approximates
net recruitment rates. If the management goal is to
achieve some degree of population recovery, e.g. to a
higher proportion of the carrying capacity level, then
removal rate would have to be less than net recruitment
rate, at least in the short term.
Acknowledgements
This study was supported financially by the Fisheries
Directorate of the Greenland Home Rule Government
and it was conducted by the Greenland Fisheries
Research Institute. Danish Air Survey ApS provided
the aircraft and the pilot, Leif Petersen, who skilfully
operated the aircraft and contributed to the data
72
M. P. Heide-Jørgensen and R. R. Reeves
collection. The other observers, Jonas Teilmann in 1993
and Jette Jensen in 1994, also deserve our sincere thanks.
Hans Valeur from the Danish Meteorological Institute
was most helpful in providing satellite images of ice
conditions in West Greenland. We thank Carsten
B. Pedersen for statistical assistance and Stephen T.
Buckland for critical comments on the manuscript.
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