197 
The effect of sea state on estimates of abundance 
for beluga whales ( De/phinapterus leucas ) 
in Norton Sound, Alaska 
Douglas P. DeMaster 
National Marine Mammal Laboratory 
National Marine Fisheries Service, NOAA 
7600 Sand Point Way, NE 
Seattle, Washington 98115 
E-mail address: douglas demaster@noaa.gov 
Lloyd F. Lowry 
Kathryn J. Frost 
Alaska Department of Fish and Game 
1300 College Road 
Fairbanks, Alaska 99701 
Rebecca A. Bengtson 
National Marine Mammal Laboratory 
National Marine Fisheries Service, NOAA 
7600 Sand Point Way, NE 
Seattle, Washington 98115 
Beluga whales (De/phinapterus leucas ) 
are relatively small odontocete ceta- 
ceans; standard lengths of newborn 
calves are about 160 cm and adults 
range from 300 to 450 cm (Doidge, 
1990). At birth, calves are dark slate 
gray, and the color gradually lightens 
until they become pure white as adults 
(Brodie, 1989). When actively swim- 
ming or diving, their bodies break 
the surface only for brief periods. 
Frost et al. (1985) reported that the 
average length of surfacing intervals 
for two radio-tagged beluga whales 
were 0.9-2. 2 seconds. 
Aerial surveys are the most com- 
mon method for estimating the abun- 
dance of beluga whales (e.g. Frost and 
Lowry, 1990; Richard et al., 1990; and 
Harwood et al., 1996). Beluga whales 
are readily seen from aircraft in calm, 
clear waters but become increasingly 
difficult to detect when the water is 
murky or when whitecaps are pres- 
ent. Although a reduction in detect- 
ability in higher sea states is expected, 
there have been no published reports 
to quantify this effect on beluga whale 
counts. Rather, researchers have usu- 
ally restricted survey effort to condi- 
tions where whitecaps are uncommon 
(see Harwood et al., 1996). Under those 
conditions, it has been assumed that 
the probability of detecting a beluga, 
given it is at or near the surface, is in- 
dependent of sea state. 
Beluga whales are one of the more 
important species of marine mammals 
used by native subsistence hunters in 
Alaska, Canada, Greenland, and Rus- 
sia (Lowry et al., 1989; Reeves, 1990; 
Harwood et al., 1996). To facilitate the 
sustained use of beluga whales by sub- 
sistence-based communities through- 
out the Arctic, it is necessary to deter- 
mine safe levels for annual removals. 
One piece of information required for 
developing guidelines for these remov- 
als is a realistic estimate of the mini- 
mum population size (Wade, 1998). In 
the past, counts of beluga whales have 
been converted to estimates of abun- 
dance by using correction factors based 
on the following probabilities: 1) the 
probability that an animal is unavail- 
able to be observed because of being 
submerged (Frost and Lowry 1 ); 2) the 
probability that an adult-size animal 
at the surface was missed (Hobbs 2 ); 
and 3) the probability a calf or year- 
ling at the surface was missed (Brodie, 
1971). We report the results of an anal- 
ysis designed to determine whether 
sea state, as measured by the Beaufort 
(BF) scale, affects beluga whale den- 
sity estimates. If such an effect is sig- 
nificant within the range of sea states 
that are routinely surveyed, failure to 
consider sea state effects would pro- 
duce negatively biased estimates of be- 
luga whale abundance. 
Methods 
Beluga whale aerial surveys were 
flown in the vicinity of Norton Sound, 
Alaska (Fig. 1), in June 1993, 1994, 
and 1995. Two primary observers were 
used during the line-transect surveys, 
one looking out each side of the air- 
craft. Within any particular year, the 
same observers flew the entire survey 
period and did not rotate positions. 
Surveys were flown between the hours 
of 0900 and 1800 local time. The survey 
was done in a passing mode, where 
whales were counted, while the survey 
aircraft remained on the trackline. 
The survey aircraft was a twin- 
engine, high-wing Aero Commander. 
Mean air speed was 220 km/h during 
surveys, and the target survey altitude 
was 330 m. However, when cloud cover 
precluded survey effort at 330 m, the 
survey altitude was reduced to 264 m. 
Each of the viewing ports contained a 
flat window, which was marked with 
a grease pencil to establish five con- 
secutive “bins” for recording sightings 
(Lowry and DeMaster 3 ). An inclinome- 
1 Frost, K. J., and L.F. Lowry. 1995. Radio- 
tag based correction factors for use in 
beluga whale population estimation. 
Working paper for the Alaska Beluga 
Whale Committee, Scient ific Workshop, 5-7 
April 1995. (Available from ADF&G, 1300 
College Road, Fairbanks, AK 99701.1 
2 Hobbs, R. 1998. Personal commun. Na- 
tional Marine Mammal Laboratory, 7600 
Sand Point Way, NE., Seattle, WA 98115. 
3 Lowry, L. F., and D. P. DeMaster. 1996. 
Beluga whale surveys in Norton Sound, 
Alaska: June 1995. Alaska Beluga Whale 
Committee Report 96-2, 6 p. (Available 
from ADF&G, 1300 College Road, Fair- 
banks, AK 99701.] 
Manuscript accepted 11 August 2000. 
Fish. Bull. 99:197-201 (2001). 
