FISHERY BULLETIN: VOL. 86, NO, 3 



Table 4.— Estimated abundance of harbor porpoise in each of the 

 eight geographic strata based on the primary model of offshore 

 distribution. Estimates for Beaufort & 1 and for Beaufort 2 were 

 computed separately and then averaged, weighting by transect 

 length. Pooled estimates for the eight strata were obtained as an 

 average of the two surveys, weighting by transect length. All esti- 

 mates are adjusted for missed animals. Standard errors are in 

 parentheses. 



Geographic 

 region 



Survey 1 



Survey 3 



Pooled 

 estimates 



1 



2 



3 



4 



5 



6 



7 



8 



Totals 

 Regions 1-3 



Regions 1-7 



Regions 1-8 



2,401 

 (2,180) 







6,909 

 (2,959) 



11,245 

 (6,943) 



9,061 

 (2,724) 



16,934 

 (7,097) 



9,808 

 (4,311) 



2,401 

 (2,180) 



46,550 

 (10,932) 



56,358 

 (11,751) 



126 

 (68) 



932 

 (646) 



153 

 (158) 



9,096 

 (9,855) 



3,296 

 (1,410) 



12,786 

 (3,676) 



5,641 

 (2,424) 



1,210 

 (669) 



32,029 

 (10,906) 



96 



(52) 



1,459 

 (885) 



112 

 (116) 



7,909 

 (4,784) 



4,806 

 (1,745) 



11,107 

 (2,363) 



10,416 

 (3,311) 



9,808 

 (4,311) 



1,667 

 (895) 



35,904 

 (6,578) 



45,713 

 (7,865) 



DISCUSSION 



Distribution 



Harbor porpoise are not uniformly distributed 

 between Cape Flattery and Point Conception. Al- 

 though there are no obvious discontinuities within 

 this range, density varies geographically and tem- 

 porally. The most dramatic temporal changes are 

 between the two September surveys and the Janu- 

 ary-February survey (Fig. 1). The coasts of Wash- 

 ington and northern Oregon were found to have 

 relatively high densities of harbor porpoise in Sep- 

 tember, but, despite excellent sighting conditions, 

 very few porpoise were seen there in January. High 

 densities of harbor porpoise were also seen in 

 Monterey Bay on both September cruises and on 

 survey 4 in May. This area was intensively surveyed 

 in February, and few harbor porpoise were seen. As 

 can be seen in Figure 1, adjacent areas tended to 

 have similar densities within a survey. Less consis- 

 tency is found when the same areas are compared 

 between different surveys. 



Table 5.— Estimated abundance of harbor porpoise in central 

 California (regions 1-3) and along the entire coast (regions 1-8) 

 based on two alternate models of offshore distribution. All 

 estimates are adjusted for missed animals. Standard errors are 

 in parentheses. 



Survey 1 Survey 3 



Pooled 

 estimates 



Alternate Model b 

 Regions 1-3 



Regions 1-8 



Alternate Model c 

 Regions 1-3 



Regions 1-8 



3,966 

 (3,602) 



95,132 

 (19,515) 



1,505 

 (1,367) 



35,736 

 (7,550) 



1,986 

 (1,104) 



770 

 (421) 



2,744 

 (1,478) 



78,019 

 (13,356) 



1,054 

 (561) 



28,769 

 (4,995) 



The apparent changes in distribution could be 

 caused by small changes in depth distributions. The 

 majority of survey effort was along the 18 m iso- 

 bath. A large fraction of animals could be missed 

 if their depth distribution changed by 10 m or less. 

 More information on depth distributions is needed 

 before the apparent temporal changes in geographic 

 distribution can be interpreted. 



Porpoise Density 



Estimates of harbor porpoise density ranged from 

 0.03 to 2.8 animals/km^ along transect lines in the 

 eight geographic regions (pooled estimates, Table 

 2). In another study, Szczepaniak (fn. 9) estimated 

 0-1.9 porpoise/km^ in four study areas in the Gulf 

 of the Farallones, CA. Taylor and Dawson (1984) 

 found 1.2-5.9 porpoise/km- at study sites in Glacier 

 Bay, AK. Flaherty and Stark^^ estimated 0.8-1.6 

 porpoise/km^ in Washington Sound. Densities in 

 the present study are therefore within the range of 

 densities found in other areas along the same coast. 



Harbor porpoise density was estimated for 

 California, Oregon, and Washington based on aerial 

 surveys that were concurrent with the present study 

 (Barlow et al. 1988). The overall estimate of harbor 

 porpoise density from that study (corrected for 

 missed animals) was 1.79 porpoise/km^. The overall 

 estimate from the ship survey (1.33 porpoise/km^) 

 can be corrected for missed animals to yield an 

 estimate of 1.73 porpoise/km^. Given that the coef- 



I'Flaherty, C, and S. Stark. 1982. Harbor porpoise {Phocoena 

 phocoena) assessment in "Washington Sound". Final Report 

 #80-ABA-3584 submitted to National Marine Mammal Laboratory, 

 National Marine Fisheries Service, NOAA, 7600 Sand Point Way, 

 NE, Seattle, WA 98115. 84 p. 



428 



