Preliminary estimates of harbor porpoise abundance in Pacific Coast waters of California, Oregon, and Washington, 2007 - 2012

"In this report, we present preliminary estimates of harbor porpoise abundance along the Pacific Coast of California, Oregon and Washington based on aerial line-transect surveys conducted between 2007 and 2012. Surveys were conducted in support of monitoring efforts for harbor porpoise (Phocoena phocoena) between central California and southern Oregon, and leatherback turtles (Dermochelys coriacea) in central California, northern Oregon, and Washington. Annual coverage and survey intensity varied by region, and two similar survey platforms were used (Partenavia and Twin Otter aircraft). For the Morro Bay and Monterey Bay harbor porpoise stocks, abundance was estimated based on previously established transects and based on alternate fine-scale transects. A geographically stratified line-transect analysis, with aircraft type as a covariate, was performed to estimate abundance (N) for the five harbor porpoise stocks found in this region: Morro Bay, N = 2,572 (coefficient of variation, CV = 0.44) for the traditional transects or N = 2,917 (CV = 0.41) for the fine-scale transects; Monterey Bay, N = 3,650 (CV = 0.46) and N = 3,715 (CV = 0.51) for traditional and fine-scale transects, respectively; San Francisco-Russian River, N = 9,886 (CV = 0.51); Northern California- Southern Oregon, N = 35,769 (CV = 0.52); and Northern Oregon-Washington Coast, N = 2 21,487 (CV = 0.44). Fine-scale survey estimates for Morro Bay and Monterey Bay stocks are similar to those using the previous transect design, but require less replication and may be a more cost-effective option for future surveys. Stock abundance estimates are similar to or greater than those reported from 2002-2007 survey data, but further analyses will be required to evaluate potential trends statistically." Karin A. Forney, James V. Carretta, and Scott R. Benson. "August 2014." System requirements: Adobe Acrobat Reader. Includes bibliographical references (pages 10-12).