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Fishery Bulletin 113(3) 
Figure 3 
Sightings of harbor porpoise (Phocoena phocoena) and completed tracklines for line- 
transect surveys conducted in the inland waters of Southeast Alaska during summer 
in (A) 2006 and (B) 2007. 
Completed tracklines and harbor porpoise sightings 
are depicted for each of the 3 periods in Figures 2-4. 
Estimation of detection probability 
Parameter estimates for the models most supported by 
AIC for each period are presented in Table 3, and their 
equivalent detection functions are illustrated in Fig- 
ure 5. Estimation of P varied between 0.47 (coefficient 
of variation [CV]=0.04) and 0.61 (CV=0.04). The half- 
normal model with a Beaufort category covariate was 
selected as the best fit for the periods 1991-1993 and 
2010-2012, and the hazard rate model without covari- 
ates was the most supported model in 2006-2007. 
Encounter rates and estimation of group size 
Sightings and group encounter rates are presented in 
Table 4. The total number of harbor porpoise groups 
seen in inland waters in Southeast Alaska during the 
summer was 422, 137, and 434 for the periods 1991- 
1993, 2006-2007, and 2010-2012, respectively. How- 
ever, because of truncation of perpendicular distance 
data, the number of sightings used in the estimation 
of density was 381, 130, and 412 for each period. The 
greatest average encounter rate was observed in the 
period 2010-2012 (0.07 groups/km, CV=0.17) and the 
lowest was recorded within the period 2006-2007 
(0.05 groups/km, CV=0.20). Expected average group 
sizes (Table 5) ranged from 1.37 (CV=0.03, during 
2010-2012) to 1.59 individuals/group (CV=0.05, during 
1991-1993). 
Estimation of density and abundance 
Stratum-specific estimates of density and abundance 
of harbor porpoise in Southeast Alaska during the 
summer are summarized in Table 6. Overall, density 
was similarly high in the earliest (1991-1993, density 
(D)=0.06, CV=0.13) and the latest (2010-2012, D=0.06, 
CV=0.10) periods. In contrast, density declined by 
half during the period 2006-2007 (D=0.03, CV=0.20). 
Overall estimates of abundance indicated a significant 
decline in the numbers of Southeast Alaska harbor 
porpoise from the levels observed in the early 1990s 
(A=1076, 95% 01=910-1272) to the mid-2000s (A/=604, 
95% 01=468-780) a drop that was followed by a signifi- 
cant increase in the early 2010s (N=975, 95% 01=857- 
1109) when the population reached numbers similar to 
those observed 20 years earlier (Table 6, Fig. 6). 
Regions of higher density were consistently found 
near Glacier Bay and Icy Strait (region 1; the northern 
region of the study area) and around Zarembo Island 
and the town of Wrangell (region 5; the southern re- 
gion of the study area), with mean densities in these 2 
regions nearly 2 and 4 times greater, respectively, than 
the mean overall density of harbor porpoise in South- 
east Alaska. Abundance in these 2 regions correspond- 
ed to 75-88% of the overall harbor porpoise abundance 
in the study area (Table 6), but trends in abundance 
differed between them. Although region 5, with Zarem- 
bo Island and Wrangell, showed a pattern similar to 
the one seen in the whole of Southeast Alaska, that is 
to say, they showed a significant decline from the early 
1990s to the mid-20G0s followed by a significant in- 
