Harbor Porpoise Aerial Survey

We use aircraft to conduct line-transect cetacean abundance surveys and photogrammetric surveys to estimate the abundance of pinnipeds at rookeries along the U.S. west coast and Mexico. Aerial surveys are a cost-effective way of surveying large regions over short periods of time. We have used Partenavia P-68 aircraft, such as the one shown, in support of U.S. Navy ship shock trial mitigation efforts.

The primary objective of this project is to estimate abundance and trends of harbor porpoise (Phocoena phocoena) in central and northern California. A secondary objective is to conduct habitat studies of harbor porpoise in central California. Aerial surveys are used to test the following two hypotheses about harbor porpoise populations along the California coastline:

  • H1: There are no trends in abundance of harbor porpoise in central and northern California.
  • H2: Harbor porpoise are distributed randomly with respect to oceanographic variables, such as sea surface temperature.

In addition to testing the above hypotheses, the project will also estimate the abundance harbor porpoise in central and northen California every 2-5 years, as required under the Marine Mammal Protection Act.

In central California, harbor porpoise have been impacted by coastal gillnets since the late 1970s. In recent years, they have been declared a ‘strategic’stock under the MMPA because of high incidental fishery mortality. The responsible fisheries have now been closed (effective Sep 2002), and the population is now expected to recover. Under the MMPA, the SWFSC is responsible for obtaining abundance estimates every 2-5 years, to monitor the health, status, and trends of this population.

Methods will follow those used during previous surveys, as described in Forney et al. (1991), using standard line transect methods from a twin-engine, high-wing airplane flying at 650 feet altitude. The low altitude is required because of the small body size of harbor porpoise. Multiple replicate surveys will be flown, as weather permits, primarily from Aug 15-Nov 15 of each year along standardized transects. Additional surveys may be flown at other times of the year to conduct habitat studies in areas of harbor porpoise concentration. Data will be analyzed using line transect methods and generalized linear/additive models (Forney 1999).

The principle investigator is Dr. Karin Forney of the Southwest Fisheries Science Center, who also conducts the field work, along with Scott Benson.


Forney, K.A., J.V. Carretta, and S.R. Benson. 2014. Preliminary estimates of harbor porpoise abundance in Pacific Coast waters of California, Oregon and Washington, 2007-2012  NOAA Technical Memorandum, NOAA-TM-NMFS-SWFSC-537. 21 p.

Carretta, J.V., K.A. Forney, and S.R. Benson. 2009. Preliminary estimates of harbor porpoise abundance in California waters from 2002 to 2007. U.S. Department of Commerce, NOAA Technical Memorandum, NOAA-TM-NMFS-SWFSC-435. 10p.

Forney, K.A., D.A. Hanan, and J. Barlow. 1991. Detecting trends in harbor porpoise abundance from aerial surveys using analysis of covariance. Fish. Bull. 89:367-377.

Forney, K. A. 1999. Trends in harbor porpoise abundance off central California 1986-95: evidence for interannual changes in distribution? Journal of Cetacean Research and Management 1:73-80.



Last modified: 9/9/2015