808 
Abstract .—Boat surveys along ran- 
domly placed line transects were con- 
ducted from June to August 1991 and 
June to October 1992 to determine dis- 
tribution and abundance of and habi- 
tat use by harbor porpoise ( Phocoena 
phocoena) off the northern San Juan Is- 
lands, Washington. There were 301 
sightings (average 4.4 sightings/h) of 
526 harbor porpoise during 73 random 
boat surveys, with group sizes of 1 to 8 
individuals (mean = 1.87, SE=0.06, 
=278). An estimated 299 harbor por- 
poise (1.26 porpoise/km 2 , SE=0.20) 
were distributed in an aggregated pat- 
tern within a 237 km 2 area (10% of 
Washington Sound), indicating that a 
large proportion (30%) of harbor por- 
poise in Washington Sound occur in the 
northern San Juan Islands. Harbor 
porpoise were distributed over a depth 
range from 20.1 to 235.0 m (mean= 
141.6 m, SE=2.43, n= 275) and were 
observed more than expected (P<0.05) 
in depths greater than 125 m and over 
shallow slopes ( < 10%) and observed 
less than expected (P<0.05) in depths 
less than 75 m. Porpoise occurred at sea 
surface temperatures of 10. 1° to 16.3°C 
and were sighted more frequently than 
expected (P<0.05) in water tempera- 
tures of 11° to 12°C. Boat surveys along 
fixed location transects indicated dis- 
tribution was similar between 1991 and 
1992. The occurrence of harbor porpoise 
in deep water, at cooler sea surface tem- 
peratures, over shallow sloping seaf- 
loor, and in tidally mixed regions (ow- 
ing to currents and tide rips) within our 
study area may, collectively, affect prey 
distribution and associated harbor por- 
poise distribution. 
Manuscript accepted 12 March 1998. 
Fish. Bull. 96:808-822 (1998). 
Distribution and abundance of and 
habitat use by harbor porpoise, 
Phocoena phocoena, off the northern 
San Juan Islands, Washington 
Kimberly L. Raum-Suryan 
James T. Harvey 
Moss Landing Marine Laboratories 
RO. Box 450 
Moss Landing, California 95039 
Present address (for K. L. Raum-Suryan): Alaska Department of Fish and Game 
Division of Wildlife Conservation 
333 Raspberry Road 
Anchorage, Alaska 995 ! 8 
E-mail address (for K. L. Raum-Suryan): kimr@fishgame. state. ak. us 
Harbor porpoise (Phocoena phocoena) 
are present year-round off the coast 
and inland waters of Washington 
State. Historically, harbor porpoise 
have been present throughout the 
Strait of Juan de Fuca, Washington 
Sound (San Juan Island archi- 
pelago), and south in Puget Sound. 
Once considered the most common 
cetacean in southern Puget Sound 
(Scheffer and Slipp, 1948), harbor 
porpoise sightings are now rare 
(Everitt et al., 1980; Calambokidis 
et al., 1984, 1985). Although harbor 
porpoise have not been sighted off 
the central San Juan Islands in re- 
cent years (Flaherty and Stark 1 ; 
Calambokidis et al. 2 ), sightings off 
the northern San Juan Islands have 
been common (Flaherty and Stark 1 ; 
Calambokidis et al. 2 ). Reasons for the 
disappearance of harbor porpoise 
from South Puget Sound are unclear 
but may be due to reduced availabil- 
ity of prey (because of changes in en- 
vironmental conditions), fishing pres- 
sure, disturbance, net entanglement, 
or pollution. 
Many biological (e.g. prey) and 
physical oceanographic factors (e.g. 
depth, seafloor relief, tidal currents, 
and sea surface temperature) affect 
the distribution of cetaceans. In- 
creased availability of prey in deep 
waters may be a factor affecting the 
distribution of harbor porpoise. 
Smith and Gaskin (1983) found a 
significant positive correlation be- 
tween abundance of mother-and- 
calf pairs and bottom depth and 
copepod ( Calanus spp.) density. 
Abundance of harbor porpoise also 
was positively correlated with depth 
and physiographic features that con- 
centrated Atlantic herring ( Clupea 
harengus) in near-surface waters 
(Watts and Gaskin, 1985). In Fish 
Harbor, New Brunswick, Canada, 
harbor porpoise were associated 
with reduced sea surface tempera- 
tures that coincided with a large in- 
flux of juvenile herring in the region 
(Gaskin and Watson, 1985). Tidal 
state affected movements of harbor 
porpoise in the Bay of Fundy; har- 
1 Flaherty, C., and S. Stark. 1982. Harbor 
porpoise (Phocoena phocoena ) assessment 
in “Washington Sound.” Final report for 
subcontract 80-ABA-3584. National Ma- 
rine Mammal Laboratory, Natl. Mar. Fish. 
Serv., NOAA, 7600 Sand Point Way NE, 
Seattle, WA, 84 p. 
2 Calambokidis, J., J. C. Cubbage, J. R. 
Evenson, S. J. Jeffries, and R. F. Brown. 
1993. Abundance estimates of harbor 
porpoise in Washington and Oregon 
waters. Final Report to National Marine 
Mammal Laboratory, Natl. Mar. Fish. 
Serv., NOAA, 7600 Sand Point Way NE, 
Seattle, WA, 55 p. 
