Raum-Suryan and Harvey: Distribution and abundance of and habitat use by Phocoena phocoena 
813 
Figure 3 
Location of 301 harbor porpoise sightings made during 73 random boat surveys completed 
from June to October 1992 within five stratified sections (A, B, C, D, E). 
tions combined, we estimated 
that the effective half-strip 
width (ESW) was 337 m (95% 
CI=307-371 m; coefficient of 
variation, CV=0.048), with an 
f( 0) of 2.96/km (SE = 0.14, 
CI=2.70-3.25, CV=0.048). 
No significant correlation 
(r=0.097, n= 250, P=0.938) was 
detected between harbor por- 
poise group size and perpen- 
dicular distance from the track- 
line. For surveys conducted 
during Beaufort <1 (re =70) in all 
sections (A-E), the mean group 
size was 1.91 harbor porpoise 
(SE=0.07, n= 250; Table 1) and 
mean density was 1.26 harbor 
porpoise/km 2 (SE=0.20; Table 
1). Harbor porpoise densities 
were least in section A (0.60 
porpoise/km 2 , SE = 0.21) and 
greatest in section D (2.3 por- 
poise/km 2 , SE=0.74; Table 1). 
There were an estimated 299 
harbor porpoise (CI=2 19-409) 
in all sections (Table 1), ranging from 
30 harbor porpoise (CI= 5-60) in sec- 
tion A to 116 harbor porpoise (CI=62- 
221) in section D (Table 1). The pooled 
estimate of harbor porpoise abundance 
(299 porpoise) for all sections yielded 
the same abundance estimate as add- 
ing the estimates for each individual 
strata (A-E; Table 1). 
If the present surveys were con- 
ducted annually with a similar sam- 
pling regime that produced an equally 
low CV (0.159), there would be suffi- 
cient power (80%) to detect a 14% an- 
nual change (a=0.05; 12% change for 
a=0.10) after five years. 
Mean number of harbor porpoise per 
survey was greatest in section D and 
least in section E (Fig. 5A). Mean 
depth throughout the study area was 
108.1 m (SE=21.68, n=584); section D 
had the greatest mean depth and sec- 
tion E the least (Fig. 5B). Harbor por- 
poise were distributed over a depth 
range of 20.1 to 235.0 m (mean=141.6 
m, SE=2.43, n- 275), with 83% of harbor porpoise 
sightings occurring over depths greater than 100 m. 
Significantly (P<0.05) fewer than expected harbor 
porpoise occurred in depths less than 75 m and sig- 
nificantly (P<0.05) more than expected in depth cat- 
egories greater than 100 m (Fig. 6). The effect size 
(degree to which depths differed among categories) 
was small and the power to detect a difference was 
