Hobbs and Waite: Abundance of Phocoena phocoena in three Alaska regions 
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164°W 160°W 156°W 152°W 148°W 144W 
Figure 3 
Completed survey transects and sightings (circles) of harbor porpoise (Phocoena phocoena) during 
the 1998 aerial survey and the 1998 beluga whale aerial survey (triangles) in the Gulf of Alaska 
stock region. Also shown are transects and sightings of harbor porpoise made during the 1999 
aerial survey south of the Alaska Peninsula and west of Chignik Bay. 
survey experience. Based on this ad hoc assessment of 
discrepancies, an experienced observer was defined as 
one who had 10 or more days of observation experience 
on the survey. Species discrepancies involving harbor 
porpoise were those that led to a misidentification of 
harbor porpoise as either a Dali’s porpoise or harbor 
seal ( Phoca vitulina). 
Within the data from the first two years of the survey, 
there were 68 species identifications of harbor porpoise, 
Dali’s porpoise, and harbor seal from paired observ- 
ers. Of these 68 identifications, 52 were determined by 
paired experienced observers in the side and belly (one 
discrepancy), 12 were determined by an experienced 
side observer paired with an inexperienced belly ob- 
server (4 discrepancies), and 4 were determined by an 
inexperienced side observer paired with an experienced 
belly observer (no discrepancies). No correlation be- 
tween discrepancies and environmental conditions was 
found. To verify the observation that the inexperienced 
observers in the belly position had a higher than aver- 
age misidentification rate and determine if the rate was 
unacceptable, four possible models were compared and 
AIC was used to identify the most parsimonious model. 
The models were 1) side observers and experienced and 
inexperienced belly observers were all different (four 
parameters); 2) experienced and inexperienced side ob- 
servers and experienced belly observers were equivalent 
and inexperienced belly observers were different (two 
parameters); 3) experienced and inexperienced observ- 
ers were different but side and belly were equivalent 
(two parameters); and 4) all observers were equivalent 
(one parameter). For model 1, probabilities of a correct 
identification were >0.99 for both experienced and in- 
experienced side observers, 0.98 for experienced belly 
observers, and 0.67 for inexperienced belly observers 
with an AIC of 13.0. For model 2, side observers with 
experienced belly observers had a probability of 0.98, 
and inexperienced belly observers had a probability of 
0.67 with an AIC of 9.1. Model 3 resulted in a prob- 
ability of 0.99 for experienced observers and >0.76 for 
inexperienced observers with an AIC of 11.6. Model 4, 
a probability for all observers, was 0.96 with an AIC of 
17.6. The most parsimonious model (lowest AIC) was 
model 2, indicating that an inexperienced observer in 
the belly position had a low reliability for species iden- 
tification. Consequently, observation effort and sightings 
by inexperienced observers in the belly during their 
first 10 survey days were treated as practice and were 
not included in the subsequent analysis. Although it 
would be possible to estimate a ^(0) that accounted 
