Hobbs and Waite: Abundance of Phocoena phocoena in three Alaska regions 
261 
Table 2 
Survey parameters and abundance estimates for harbor porpoise ( Phocoena phocoena) stocks off Southeast Alaska, the Gulf of 
Alaska, and the Bering Sea in 1997, 1998, and 1999, respectively. Cook Inlet survey results are taken from a survey for beluga 
whales which followed a protocol similar to the harbor porpoise surveys. No perception bias correction was available for the 1998 
Cook Inlet survey; consequently observed abundance is used in place of total abundance for this area. The Cook Inlet abundance 
was included in the Gulf of Alaska stock total abundance. Extrapolated areas were small inlets and unsurveyed areas where the 
density of harbor porpoise was assumed to be the same as similar surveyed areas for the purpose of estimating total abundance. 
Coefficient of variation (CV) of a statistic is the standard error of the statistic divided by the statistic; confidence intervals are 
calculated by using a log-normal distribution and N min = Afe-° 842 '/ ina+cv<iv,2) . 
Southeast Alaska 
Gulf of Alaska 
Cook Inlet Survey 
Bering Sea 
Estimate 
CV(%) 
Estimate 
CV(%) 
Estimate 
CV(%) 
Estimate 
CV(%) 
Study region (km 2 ) 
106,087 
158,733 
18,948 
106,381 
Total trackline (km) 
9844 
10,127 
1355 
7849 
No. if sightings 
129 
88 
8 
201 
Average correction for 
1.560 
10.8% 
1.372 
6.6% 
1 
1.337 
6.2% 
perception bias (l/g(0)) 
Effective half strip width (km) 
0.182 
8.7% 
0.122 
5.8% 
0.280 
28.1% 
0.122 
5.8% 
Average group size (no. of individuals) 
1.279 
4.4% 
1.289 
2.3% 
1.129 
5.0% 
1.289 
2.3% 
Corrected average group density 
0.026 
16.6% 
0.048 
11.7% 
0.012 
60.5% 
0.119 
13.0% 
(groups/km 2 ) 
Average porpoise density 
0.033 
17.2% 
0.062 
11.9% 
0.013 
60.7% 
0.153 
13.2% 
(porpoise/km 2 ) 
Uncorrected abundance 
3505 
17.2% 
9791 
11.9% 
249 
60.7% 
16,289 
13.2% 
in surveyed areas 
Extrapolated area (km 2 ) 
6539 
4722 
Abundance in extrapolated area 
261 
40.5% 
449 
60.6% 
Total uncorrected abundance 
3766 
16.2% 
10,489 
11.5% 
16,289 
13.2% 
Correction for availability 
2.96 
18.0% 
2.96 
18.0% 
2.96 
18.0% 
(from Laake, et al., 1997) 
Average perception correction 
4.62 
21.0% 
4.06 
19.2% 
2.96 
18.0% 
3.96 
19.0% 
x availability correction 
Total abundance (A0 
11,146 
24.2% 
31,046 
21.4% 
48,215 
22.3% 
9116 
25,987 
40,039 
Lower 95% confidence limit 
6980 
20,520 
31,285 
Upper 95% confidence limit 
17,788 
46,972 
74,308 
Table 1). The abundance estimate for the GOA stock, 
which included the Cook Inlet harbor porpoise abun- 
dance estimate, was 31,046 animals (CV=21.4%; 
2V min =25,987, Table 1), and the abundance estimate 
for the BS stock was estimated as 48,215 animals 
(CV=22.3%; Af min =40,039, Table 1). 
Discussion 
Habitat type may account for the increase in density of 
harbor porpoise from east to west — at least for the much 
higher abundance of the BS stock compared to the other 
two stocks. The Bering Sea encompasses a vast sea 
ranging from a large shallow bay (Bristol Bay) extend- 
ing to a large shelf that descends to the abyssal sea. 
Our entire survey of this stock region was conducted 
in Bristol Bay where water depth never exceeds 100 m. 
In contrast, the shelf area is narrower in the Gulf of 
Alaska so that the surveys off Southeast Alaska and in 
the Gulf of Alaska were routinely conducted in waters 
up to 200 m, and occasionally up to 1800 m. Despite 
the greater ranges of depths surveyed in Southeast 
Alaska and the Gulf of Alaska, harbor porpoise were 
present primarily in waters less than 100 m in depth. 
Off northern California, higher than expected numbers 
of harbor porpoise were found between the 20 m to 60 m 
isobaths and fewer than expected in waters deeper than 
60 m (Carretta et ah, 2001). Similarly, Barlow (1988) 
found harbor porpoise primarily distributed in waters 
shallower than 110 m in depth. In contrast, Raum- 
Suryan and Harvey (1998) found that harbor porpoise 
near the northern San Juan Islands, Washington, were 
present at depths greater than 100 m. Differences in 
