Dahlheim et al.: Temporal changes in abundance of Phocoena phocoena inhabiting the inland waters of Southeast Alaska 
251 
Distance (km) 
Distance (km) 
Distance (km) 
Figure 5 
Detection probability models that fit perpendicular distance data collected during surveys of harbor porpoise ( Phocoena 
phocoena) in Southeast Alaska for the following periods and models: (A) 1991-1993, half normal (hn)+Beaufort sea state; 
(B) 2006-2007, hazard rate; and (C) 2010-2012, hn+Beaufort sea state. 
harbor porpoise, possibly because most groups were ob- 
served well within the maximum detection range pro- 
vided by each ship. Animal responses may have varied 
on the basis of the noise profiles transmitted by these 
different platforms. If animals move toward or away 
from the survey platform during line-transect surveys, 
density estimates will be over- or underestimated, re- 
spectively. Palka and Hammond (2001) reported that 
North Atlantic harbor porpoise avoided the survey plat- 
form. However, Williams and Thomas (2007) reported 
that responsive movement toward or away from sur- 
vey platforms was not pronounced for harbor porpoise 
that occupied the coastal waters of British Columbia. 
During our investigations, we did not observe harbor 
porpoise responding to our survey platform; however, 
quantitative data that addressed porpoise avoidance or 
attraction were not collected. 
It is unlikely that we missed areas with high den- 
sities of harbor porpoise given the extent of our spa- 
tial coverage and the long-term nature of our study. 
In addition to the 8 summer surveys reported here 
(in 1991-1993, 2006-2007, 2010-2012), we also con- 
ducted 5 line-transect surveys each in the spring and 
fall (Table 1). Some areas typically not covered during 
our line-transect surveys (e.g., when we were off effort 
while entering bays and inlets to anchor for the night, 
finding shelter from storms, or conducting studies on 
killer whales; see Dahlheim and White, 2010) did not 
reveal any other regions of high porpoise densities. In 
addition, between 1994 and 2005, 24 more vessel sur- 
veys, during which line-transect methods were not car- 
ried out throughout this study area, found no other ar- 
eas of high porpoise densities (Dahlheim et al., 2009). 
An aerial study conducted in 1997 (Hobbs and Waite, 
2010) included some additional survey areas in South- 
east Alaska but also did not reveal any other locations 
with high densities of harbor porpoise. Interviews with 
other researchers, local residents, and fishermen famil- 
Tahle 6 
Summer density (D; individuals/km 2 ) and abundance (TV; number of individuals) of harbor porpoise ( Phocoena phocoena ) 
from surveys conducted in the inland waters of Southeast Alaska during the periods 1991-1993, 2006-2007, and 2010-2012. 
CV=coefficient of variation. 
1991-1993 2006-2007 2010-2012 
Region 
Region name 
D 
N 
CV 
D 
N 
CV 
D 
N 
CV 
1 
Cross Sound, Icy Strait, and Glacier Bay 
0.15 
342 
0.14 
0.13 
297 
0.31 
0.14 
332 
0.14 
2 
Lynn Canal and Stephens Passage 
0.03 
65 
0.24 
0.02 
35 
0.44 
0.02 
40 
0.42 
3 
Frederick Sound 
0.03 
81 
0.32 
0.02 
64 
0.41 
0.01 
30 
0.54 
4 
Upper and Lower Chatham Strait 
0.02 
68 
0.31 
0.01 
26 
0.56 
0.01 
25 
0.04 
5 
Sumner Strait, Wrangell, and Zarembo Island 
0.16 
461 
0.25 
0.06 
182 
0.29 
0.18 
526 
0.15 
6 
Clarence Strait to Ketchikan 
0.02 
60 
0.45 
0.00 
0 
0.00 
0.01 
21 
0.49 
Total 
0.06 
1076 
0.13 
0.03 
604 
0.20 
0.06 
975 
0.10 
