200 
Fishery Bulletin 99(1 ) 
in BF sea states 2, 3, and 4. The average density in BF 
sea state 1 (0.206 whales/km 2 ) was more than three times 
greater than the average density in BF sea states 2, 3, 
and 4 (0.068 whales/km 2 , SE=0.009). Further, the average 
density in BF sea state 1 was greater than the average 
density observed in any individual year by a factor of two 
or more. That is, the average density estimates (whales 
sighted/km 2 ) for beluga whales derived from our surveys 
in 1993, 1994, and 1995 were 0.074 (SE=0.023), 0.083 
(SE=0.027), and 0.097 (SE=0.035), respectively (Lowry and 
DeMaster 3 ) compared with an average density of 0.206 
whales/km 2 for BF sea state 1. 
A preliminary estimate for a correction factor that would 
account for sea state, based on the ratio of the estimated 
average density for BF sea state 1 in relation to the 
weighted average density in BF sea states 2, 3, and 4, 
is 3.023 (CV=0.285). Given our inability to discriminate 
among density estimates for BF sea states 2, 3, and 4, it is 
not possible at this time to develop a BF-specific correction 
factor for Norton Sound beluga whale surveys. 
As noted earlier, we did not observe coherent groups of 
beluga whales during the survey, although they were ag- 
gregated in their general distribution. Therefore, we have 
not reported on the effect of sea state on estimates of 
group size. Further, because surveys were conducted at 
survey altitudes of either 264 m or 330 m in some years, 
interpreting the effect of sea state on average effective 
strip width (ESW) was not possible. However, the avail- 
able data for a given year at a constant altitude (i.e. 330 m) 
indicated that there was not a significant relationship be- 
tween sea state and ESW. For example, in 1994 the ESWs 
for BF sea states 1, 2, 3, and 4, were 0.35, 0.58, 0.54, 0.20 
km, respectively, where there were no significant differ- 
ences in ESW for a given sea state. The effect of sea state 
on encounter rate (i.e. number of sightings per km of sur- 
vey effort), as noted earlier, was significant (Table 3). Not 
surprisingly, the same pattern reported for estimated den- 
sity versus sea state was observed for encounter rate. That 
is, the encounter rate for BF sea state 1 (0.28 sightings/ 
km) was significantly greater than the encounter rates for 
BF sea states 2, 3, or 4 (0.11, 0.11, and 0.04 sightings/km, 
respectively). 
Beluga whale aerial surveys are flown in a variety of 
conditions and with methods adapted to regional circum- 
stances. The results and conclusions presented in this 
note relate specifically to line-transect surveys in the Nor- 
ton Sound region flown in an airplane similarly config- 
ured to the Aero Commander used in our study. Norton 
Sound is a large, exposed area and has frequent windy 
conditions. Some of the transects that we flew were very 
long, and sea state sometimes varied considerably along a 
transect. Nonetheless, because of the strong effect of sea 
state on density that we were able to detect, possible sea 
state effects should be considered in all beluga whale sur- 
veys. However, the authors recognize other factors not con- 
trolled for in our study may have influenced the results 
(e.g. behavioral responses of beluga whales to sea state). 
Clearly, additional studies are warranted. 
Several approaches that should be considered in design- 
ing aerial surveys for the purpose of estimating beluga 
whale abundance are 1) restrict survey effort to conditions 
of BF sea state 1 or less; 2) continue to survey in sea states 
higher than BF sea state 1 and incorporate sea state ef- 
fects in data analysis, 3) estimate the probability of sight- 
ing through the use of a third (independent) observer, or 4) 
increase the probability of sighting animals on the track 
line through the use of a belly window and third observer. 
The first approach is not feasible in the Norton Sound re- 
gion and might prove difficult to implement in other locali- 
ties. The latter approaches provide more flexibility in the 
field. Correction factors can then be used to adjust for re- 
duced sightings in higher sea states, or analytical models 
can be developed that incorporate sea state as a covariate, 
as was done for harbor porpoise (Phocoena phocoena) by 
Forney et al. (1991). 
Acknowledgments 
Surveys were expertly flown by Tom Blaesing. Observers 
and data recorders in addition to DeMaster, Lowry, and 
Frost, included Robert Nelson, Debbie Blaesing, and Dieter 
Betz. Funding for this study was provided by the Alaska 
Beluga Whale Committee, the National Marine Fisheries 
Service, and the Alaska Department of Fish and Game. 
Early versions of the manuscript were improved by com- 
ments from John Bengtson, Rod Hobbs, Pierre Richard, 
and Janice Waite, two anonymous reviewers, and the sci- 
entific editor. 
Literature cited 
Brodie, P. F. 
1971. A reconsideration of aspects of growth, reproduction, 
and behavior of the white whale with reference to the Cum- 
berland Sound, Baffin Island, population. J. Fish. Res. 
Can. 28:1309-1318. 
1989. The white whale Delphinapterus leucas (Pallas, 1776). 
In Handbook of marine mammals, vol. 4 (S. H. Ridgway and 
R. Harrison, eds.), p. 119-144. Academic Press, London. 
Doidge, D. W. 
1990. Age-length and length-weight comparisons in the 
beluga, Delphinapterus leucas. In Advances in research 
on the beluga whale, Delphinapterus leucas (T. G. Smith, D. 
J. St. Aubin, and J. R. Geraci, eds.), p. 59-68. Can. Bull. 
Fish. Aquat. Sci. 224, 
Eberhardt, L. L. 
1968. An approximation to a multiple-comparison test. Co- 
peia 2:314-319. 
Forney, K. A., D. A. Hanan, and J. Barlow. 
1991. Detecting trends in harbor porpoise abundance from 
aerial surveys using analysis of covariance. Fish. Bull. 
89:367-377. 
Frost, K. J., and L. F. Lowry. 
1990. Distribution, abundance, and movements of beluga 
whales, Delphinapterus leucas , in coastal waters of western 
Alaska. In Advances in research on the beluga whale, Del- 
phinapterus leucas (T. G. Smith, D. J. St. Aubin, and J. R. 
Geraci, eds.), p. 39-71. Can. Bull. Fish. Aquat. Sci. 224. 
Frost, K. J., L. F. Lowry, and R. R. Nelson. 
1985. Radiotagging studies of belukha whales in Bristol 
Bay, Alaska. Mar. Mamm. Sci. 1:191-202. 
