HARBOR PORPOISE, PHOCOENA PHOCOENA, 



ABUNDANCE ESTIMATION FOR CALIFORNIA, OREGON, AND 



WASHINGTON: II. AERIAL SURVEYS 



Jay Barlow,! Charles W. Oliver,^ Terry D. Jackson,^ and 

 Barbara L. Taylor^ 



ABSTRACT 



We conducted aerial surveys in September 1984 and September and October 1985 to determine the abun- 

 dance of harbor porpoise along the coasts of California, Oregon, and Washington. Two observers and 

 a recorder searched along predetermined transect lines at 0.61 and 1.85 km offshore. Strip transect 

 methods were used. A total of 366 groups of harbor porpoise were seen in the 9,500 linear kilometers 

 that were surveyed. Apparent density was significantly affected by sea state and cloud cover. Using 

 observations made during optimal conditions (clear skies and calm seas), apparent harbor porpoise den- 

 sity averaged 0.56 animals km'". Behavioral observations from shore and from a helicopter indicated 

 that porpoise are near the surface only 23.9% of the time. To account for this, porpoise density was 

 multiplied by a factor of 3.2, resulting in an adjusted estimate of 1.79 animals km"". Only a small percent- 

 age of the total area inhabited was surveyed under optimal sighting conditions, hence density estimates 

 were not extrapolated to estimate total porpoise abundance. Harbor porpoise density showed similar 

 patterns to those measured from ship surveys, and adjusted aerial estimates are approximately equal 

 to ship estimates. 



Harbor porpoise, Phocoena phocoena, are subject to 

 mortality in the halibut set net fishery in central 

 California (NMFS^; Diamond and Hanan^). To evalu- 

 ate the significance of this mortality, an estimate 

 of population size is needed. Two aerial surveys and 

 three ship surveys were conducted from 1984 to 

 1986 to gather information on harbor porpoise abun- 

 dance along the coasts of California, Oregon, and 

 Washington. Observations were also made from 

 shore-based stations and from a helicopter to pro- 

 vide ancillary information needed for population 

 estimation. Results and population estimates from 



'Southwest Fisheries Center La Jolla Laboratory, National 

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

 92038. 



^National Marine Fisheries Service, Southwest Region, 300 

 South Ferry Street, Terminal Island, CA 90731; present address: 

 Pacific Marine Center, NOAA, 1801 Fairview Avenue East, 

 Seattle, WA 98102. 



^National Marine Fisheries Service, National Marine Mammal 

 Laboratory, 7600 Sand Point Way, N.E., Seattle, WA 98115; 

 present address: University of California, San Diego, Department 

 of Biologj', La Jolla, CA 92093. 



^NMFS. 1980. A report based on the workshop on stock 

 assessment and incidental take of marine mammals involved in 

 commercial fishing operations. January 1980. Available from 

 National Marine Fisheries Service, National Marine Mammal 

 Laboratory, 7600 Sand Point Way NE, Seattle, WA 98115. 



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

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

 through March 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. 



the ship surveys are reported by Barlow (1988). 

 Preliminary results from the 1984 and 1985 aerial 

 surveys were presented by Oliver and Jackson^ and 

 Oliver^ respectively. Here we present population 

 density estimates based on the aerial surveys and 

 on shore and helicopter observations. 



The aerial surveys were flown in September of 

 1984 and in September and October of 1985 from 

 Point Conception, CA to Cape Flattery, WA. Sur- 

 veys were coordinated by the National Marine Fish- 

 eries Service (NMFS) in collaboration with the 

 California Department of Fish and Game, the Ore- 

 gon Department of Fish and Wildlife, and the 

 Washington Department of Wildlife. Survey design 

 was based on information given by Dohl et al.^ 

 regarding harbor porpoise distribution in California. 

 They reported that harbor porpoise were usually 



^Oliver, C. W., and T. D. Jackson. 1987. Occurrence and 

 distribution of marine mammals at sea from aerial surveys con- 

 ducted along the U.S. west coast between December 15, 1980 and 

 December 17, 1985. Adm. Rep. LJ-87-19, 189 p. Available from 

 National Marine Fisheries Service, Southwest Fisheries Center, 

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



^Oliver, C. W. 1986. Trip report: 1985 harbor porpoise aerial 

 survey, September 9 to October 15, 1985. Adm. Rep. LJ-86-21, 

 29 p. Available from National Marine Fisheries Service, South- 

 west Fisheries Center, P.O. Box 271, La Jolla, CA 92038. 



»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. 



Manuscript accepted May 1988. , 



fishery BULLETIN: VOL. 86, NO. 3, 1988. V//' ^Yj 



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