HARBOR PORPOISE, PHOCOENA PHOCOENA, 

 ABUNDANCE ESTIMATION FOR CALIFORNIA, OREGON, AND 



WASHINGTON: I. SHIP SURVEYS 



Jay Barlowi 



ABSTRACT 



The density and total population size of harbor porpoise along the coasts of California, Oregon, and 

 Washington are estimated from ship surveys using line transect methods. Surveys were completed 

 between September 1984 and May 1986 using teams of 3-5 observers. Data include 852 porpoise groups 

 sighted during 6,590 km of transects. Sighting rates varied more due to effects of sea state than due 

 to the presence of rain, fog, or sun glare. Experiments using additional observers indicate that approx- 

 imately 22% of trackline groups were missed by a team of 5 observers. Harbor porpoise density is 

 calculated from transects along the 18 m isobath and is extrapolated to other depth zones based on a 

 model of porpoise abundance as a function of depth. Total population size is estimated as 45,713 (SE 

 = 7,865) animals. 



Approximately 200-300 harbor porpoise are taken 

 annually in central California set net fisheries (Dia- 

 mond and Hanan^; Hanan, et al.^). Little is known 

 about porpoise abundance in this area. Dohl et al.* 

 estimated that 1,600-3,000 porpoise reside in cen- 

 tral and northern California based on their aerial 

 surveys of coastal cetaceans. However, because har- 

 bor porpoise are frequently missed in aerial surveys 

 (Kraus et al. 1983), this estimate is probably low. 

 More information is needed on abundance, distribu- 

 tion, and population structure to determine the 

 significance of harbor porpoise mortality in set 

 nets. 



Beginning in 1984, the National Marine Fisheries 

 Service (NMFS) has conducted ship and aerial 

 surveys of harbor porpoise abundance in California, 

 Oregon, and Washington. This report presents 

 results from four ship surveys. Results of the aerial 

 surveys are presented by Barlow et al. (1988). 



'Southwest Fisheries Center La JoUa Laboratory, National 

 Marine Fisheries Service, NOAA, P.O. Box 271, La Jolla, CA 

 92038. 



^Diamond, S. L., and D. A. Hanan. 1986. An estimate of har- 

 bor porpoise mortality in California set net fisheries: April 1, 1983 

 through May 31, 1984. Adm. Rep. SWR-86-15, 40 p. Available 

 from National Marine Fisheries Service, Southwest Region, 300 

 S. Ferry Street, Terminal Island, CA 90731. 



^Hanan, D. A., S. L. Diamond, and J. P. Scholl. 1986. An esti- 

 mate of harbor porpoise mortality in California net fisheries April 

 1, 1984 through March 31, 1985. Adm. Rep. SWR-86-16, 38 p. 

 Available from National Marine Fisheries Service, Southwest 

 Region, 300 S. Ferry Street, Terminal Island, CA 90731. 



^Dohl, T. P., R. C. Guess, M. L. Duman, R. C. Helm. 1983. 

 Cetaceans of central and northern California, 1980-83: status, 

 abundance, and distribution. Report prepared for U.S. Minerals 

 Management Service, Contract #14-12-0001-29090, 284 p. 



Porpoise density is estimated from survey data 

 using line transect models (Burnham et al. 1980). 

 Total abundance is estimated by extrapolating from 

 density observed along transect lines to the entire 

 area inhabited. Abundance in offshore regions is 

 based on a model of porpoise density as a function 

 of water depth. In addition to abundance estimation, 

 survey data are used to examine the effect of envi- 

 ronmental conditions on sighting efficiency and the 

 possibility of temporal changes in harbor porpoise 

 distribution. 



METHODS 



Ship Survey Methods 



Surveys were conducted from two National 

 Oceanic and Atmospheric Administration (NOAA) 

 research vessels, the 52 m RV David Starr Jordan 

 (Surveys 1, 3, and 4) and the 54 m RV McArthur 

 (Survey 2)^. Both vessels were of similar design with 

 viewing stations located on top of the pilothouse 

 (viewing height was approximately 10 m above sea 

 surface). Transect lines followed as close as possi- 

 ble to the 18 m isobath (roughly 2-4 km from the 

 coast), although the actual depth along the transect 

 varied from approximately 15-45 m, depending on 

 the presence of local navigational hazards. The areas 



Manuscript accepted May 1988. 



FISHERY BULLETIN: VOL. 86, NO. 3, 1988. 



^Cruise reports available from the Southwest Fisheries Center, 

 P.O. Box 271, La Jolla. CA 92038. 



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