Bradford et al.: Abundance estimates of cetaceans within the U.S. Hawaiian islands EEZ 
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Table 2 
Detection functions modeled by using pooled sightings collected in the central North Pacific during line-transect surveys 
conducted from 1986 through 2010 by the NOAA Southwest and Pacific Islands Fisheries Science Centers. The estimated 
detection functions are listed along with the associated factor levels used to test the species covariate (see text for covariate 
descriptions). Ntot is the number of available systematic and nonsystematic sightings in Beaufort sea states 0-6, and Ndet 
is the number of sightings that fell within the analytical truncation distance (TD; in kilometers). If a model with an addi¬ 
tional covariate was within 2 Akaike’s information criterion (corrected for a small sample size) units of the best-fit covariate 
model, the second covariate is shown in parentheses. 
Detection function 
Ntot 
Ndet 
TD 
Covariates tested 
Best-fit model 
Pantropical spotted dolphin 
274 
247 
4.5 
Beaufort, group size, species 
Group sizei+Beaufort) 
Pantropical spotted dolphin 
83 
73 
Other^ 
191 
174 
Species pool 1 
282 
255 
4.5 
Beaufort, group size, ship 
Shipi+group size) 
Striped dolphin 
249 
223 
Fraser’s dolphin 
23 
22 
Melon-headed whale 
7 
7 
Other 
3 
3 
Species pool 2 
231 
216 
5.0 
Beaufort, group size, species 
Group size+species 
Rough-toothed dolphin 
58 
55 
Bottlenose dolphin 
56 
50 
Risso’s dolphin 
64 
61 
Pygmy killer whale 
14 
14 
Other 
39 
36 
Species pool 3 
152 
138 
4.5 
Beaufort, group size, ship 
Null(^-s/^ip) 
Short-finned pilot whale 
138 
126 
Longman’s beaked whale 
5 
5 
Other 
9 
7 
Species pool 4 
144 
128 
5.5 
Beaufort, group size, species 
Null(^-spec^es) 
Killer whale 
34 
34 
Sperm whale 
109 
94 
Other^ 
1 
0 
Species pool 5 
143 
136 
5.0 
Beaufort, group size 
Beaufort+group size 
Blainville’s beaked whale 
7 
7 
Cuvier’s beaked whale 
46 
43 
Unidentified Mesoplodon 
39 
39 
Unidentified beaked whale 
50 
46 
Other 
1 
1 
Species pool 6 
150 
139 
5.0 
Beaufort, group size 
Nulli-i-Beaufort) 
Bryde’s whale 
81 
77 
Sei whale 
11 
9 
Fin whale 
5 
5 
Blue whale 
4 
4 
Sei or Bryde’s whale 
44 
39 
Other 
5 
5 
Unidentified rorqual 
61 
47 
5.5 
Beaufort, group size 
Null 
Unidentified dolphin 
316 
281 
5.5 
Beaufort, group size, ship 
Beaufort-i-group size 
Unidentified cetacean 
162 
144 
5.5 
Beaufort, group size 
Beauforti^group size) 
justification for testing for a species effect on this single-species detection function is provided in the text. 
^The “other” sighting in this pool was within the TD but was removed for other reasons (see text for details). 
Barlow and Forney, 2007). Sighting group size used in 
detection function modeling was a weighted geometric 
mean of the calibrated “best” estimates of group size 
made by each observer for each sighting (weighted by 
the inverse of the mean squared estimation error). 
To obtain the number of individuals of each spe¬ 
cies in sightings of mixed-species groups (as needed 
for density estimation, see the next paragraph), the 
sighting group size was multiplied by the proportion 
of each species present (averaged over all observers). 
For some sightings of mixed-species groups, the most 
abundant species within a sighted group was not one 
of the pooled species—an outcome that complicated the 
use of the species covariate. The factor level for these 
sightings was labeled as “other” to account for the col¬ 
lective influence of nonpooled species on the detection 
