Nichols et al.: Spatial and temporal distribution of Eubalaena glacialis in Cape Cod Bay 
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70° 40' W 70° 30' W 70° 20’ W 70° I O' W 70° 00' W 69° 50' W 
42° 10' N 
42° 00' N 
41° 50' N 
41° 40' N 
Figure 3 
North Atlantic right whale ( Eubalaena glacialis) sightings ( + ) 
recorded during valid aerial survey effort 1998-2002. A sight- 
ing is defined as one or more whales observed at the same time 
and location. 
method (Kenney and Winn, 1986). This method first 
quantifies survey effort as length of track line sampled, 
then expresses SPUE as the number of whales sighted 
per standardized length of track. 
The boundaries of the study area for this analysis 
were 42°09'N to 41°39'N and 70°00'W to 70°39'W (Fig. 
2). The study area was partitioned into 117 cells mea- 
suring 3 minutes of latitude (5.6 km) by 3 minutes of 
longitude (4.1 km). Each cell was 23 km 2 in area. Four- 
teen cells lay completely over land and were eliminated; 
thus there were 103 cells available to be sampled. 
Survey data comprised a chronological sequence of 
latitude and longitude points that described the path 
flown by the aircraft. Each successive pair of points de- 
scribed a track segment, and the length of that segment 
(effort) could be computed from the latitude and longi- 
tude data (Kenney and Winn, 1986). For each survey, 
each track segment was partitioned into smaller sec- 
tions contained within the separate 3-minute cells. In 
order to standardize effort further, only those segments 
were completed where visibility was at least 3.7 km, 
Beaufort sea state was 3 or lower, aircraft altitude was 
below 325 m, and observers were on watch. Similarly, 
only right whales sighted under these defined, valid ef- 
fort conditions were included in our study. We included 
only sightings identified by observers in the field as 
definite or probable right whales in the analysis; sight- 
ings identified as possible right whales were eliminated. 
A sighting was defined as one or more whales observed 
at the same time and location; for simple distribution 
maps (e.g., Fig. 3) all sightings were treated as single 
points, but the number of whales sighted is factored 
into the SPUE analysis. The sampling season was de- 
fined as December through mid-May, and was divided 
for analysis into 12 two-week periods (1 December-17 
May). Total effort and total number of right whales 
sighted within each cell were summed within periods 
and across years; then the number of whales sighted 
was divided by effort to generate the SPUE index, in 
units of whales sighted per 1000 km of valid effort. 
Cells with less than 2 km of effort (half the width of 
a cell) within a 2-week period were considered to have 
been inadequately sampled and were eliminated from 
further analyses. 
For mapping purposes, the SPUE values were ranked 
into levels. All cells with SPUE>0 were pooled, sorted 
from highest to lowest SPUE values, and separated by 
quartiles, representing the top, second highest, third, 
and bottom quarters of the distribution. The upper 
quarter was further partitioned by identifying the top 
5% of all values. These values were mapped by using 
different shadings to show the classes. The cells were 
