198 
Fishery Bulletin 99(1) 
Figure 1 
Map of the Norton Sound and Yukon River delta region showing beluga whale 
aerial survey transects flown in June 1993-95 (dashed lines). Circles reflect sight- 
ings of beluga whales, where all three years of data are combined. 
ter was used to measure sighting angles for the bins. The 
inner edge of the first sighting bin was offset 330 m from 
the center of the track line, and the outer edge of the outer 
bin was 2100 m from the center of the track line. Position 
data were collected by means of an onboard global position- 
ing system that sent data directly to a laptop computer. All 
sightings were reported by the observers to a third person 
who entered the data into the onboard laptop computer. A 
continuous record of sea state was maintained by the re- 
corder, according to the BF scale (Table 1). 
Within the study area, surveys were conducted along the 
coast and on offshore transects. Very few beluga whales 
were seen on the coastal flights and they were always on 
the shoreward side of the aircraft, very near shore. To min- 
imize the effect of very low densities of beluga whales seen 
in a wide range of BF sea states in the coastal band (de- 
fined as survey effort conducted while the aircraft was 
centered approximately 1.1 km offshore), only survey data 
from the offshore transects were used in our analysis. The 
number of on-effort track miles surveyed during offshore 
transects was 10,362 km. 
Survey data were analyzed with the computer program 
DISTANCE (Laake et al., 1994). Each sighting of beluga 
whales was considered to he a grouped cluster within a 
single sighting bin. Animals were sighted in juxtaposed 
bins only a few times. In those situations, the bin that 
included a majority of animals in the group was used to 
designate the sighting bin for that sighting. However, it 
Table 1 
Summary of the relationship between Beaufort (BF) sea 
state number, wind speed, and sea surface condition. 
BF 
Wind speed 
sea state 
(km/h) 
Sea surface conditions 
0 
0 
no ripples 
1 
1-5 
ripples, no foam on crests 
2 
6-11 
small wavelets, crests 
glassy 
3 
12-19 
large wavelets, scattered 
whitecaps 
4 
20-28 
small waves, numerous 
whitecaps 
5 
29-38 
moderate waves, many 
whitecaps, some spray 
should be noted that in this area at this time of year, 
we did not observe coherent schooling behavior of beluga 
whales. Rather, beluga whales were observed in highly 
dispersed linear aggregations. Therefore, analysis of group 
size by sea state was not undertaken because group size 
was predominantly a function of whether the transect was 
crossing or flying parallel to a “line” of beluga whales. 
