Dahlheim et al.: Temporal changes in abundance of Phocoena phocoena inhabiting the inland waters of Southeast Alaska 
247 
Table 2 
Regions identified within the study area with overall size of each stratum and the amount of survey effort 
realized during line-transect surveys for harbor porpoise (Phocoena phocoena) conducted in summer in South- 
east Alaska in 3 survey periods (1991-1993, 2008-2007, and 2010-2012). 
Survey effort (km) 
Region 
Region name 
Area (km 2 ) 
1991-1993 
2006-2007 
2010-2012 
1 
Cross Sound, Icy Strait, and Glacier Bay 
2302 
1210 
522 
1122 
2 
Lynn Canal and Stephens Passage 
1985 
740 
345 
526 
3 
Frederick Sound 
2951 
1059 
579 
1279 
4 
Upper and Lower Chatham Strait 
4267 
957 
354 
694 
5 
Sumner Strait, Wrangell, and Zarembo Island 
2943 
812 
450 
1136 
6 
Clarence Strait to Ketchikan 
3218 
533 
159 
599 
Total 
17,665 
6228 
2466 
6172 
tion to estimate the expected group size for analysis 
conducted with CDS models. For MCDS models, es- 
timates of the expected group size were obtained as 
proposed by Marques and Buckland (2003, Eq. 16 on 
p. 928). 
Estimation of abundance 
Stratum-specific abundance was estimated with the 
most supported detection probability model for each 
period. Total abundance in the survey regions was es- 
timated by summing across the estimates of each in- 
dividual stratum. Abundance and variance were esti- 
mated as in Innes et al. (2002) and Marques and Buck- 
land (2003). Lognormal 95% confidence intervals (CIs) 
(Buckland et al., 2001) were computed for abundance 
estimates for each period. 
Results 
Between 1991 and 2012, 8 line-transect surveys were 
completed during the summer in Southeast Alaska (Ta- 
ble 1). The regions (or strata) within the study area are 
depicted in Figure 1. Total and stratum-specific regions 
and realized survey effort are summarized in Table 2. 
In all regions combined, a total area of 17,665 km 2 rep- 
resenting 14,865 km of survey trackline was surveyed. 
Figure 2 
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) 1991, (B) 1992, and (C) 1993. 
