Preliminary estimates of cetacean abundance along the U.S. west coast and within four National Marine Sanctuaries during 2005

Preliminary estimates of cetacean abundance along the U.S. west coast and within four National Marine Sanctuaries during 2005 (June 2007)

Karin A. Forney

NOAA Technical Memorandum NMFS SWFSC no. 406, 27 pp.

ABSTRACT

The abundance of cetaceans along the U.S. West Coast was estimated from a ship line-transect survey conducted during 2005. The survey was designed to uniformly cover waters off California, Oregon and Washington from the coast to 300 nmi (556 km) offshore, and to provide fine-scale coverage within four of the five West Coast National Marine Sanctuaries (NMS) Preliminary abundance estimates for 19 species were calculated using a geographically stratified, multiple-covariate line-transect analysis. To increase samples sizes for estimating effective strip width based on sighting covariates, the 2005 sighting data were combined with data from four similar surveys conducted during 1991-2001. Trackline detection probabilities were obtained from other studies that used the same survey methods. Broad geographic strata for analysis included Southern California (south of Point Conception), Central and Northern California, and Oregon/Washington; fine-scale strata included the Olympic Coast NMS, adjacent areas over the continental slope and in Canadian waters, and the three combined central California NMS. As in past years, the most abundant species coastwide was the short-beaked common dolphin (Delphinus delphis), and the most abundant whale was the fin whale (Balaenoptera physalus). Off Oregon and Washington, Dall's porpoise (Phocoenoides dalli) was the most abundant species. Within the NMS, humpback whales (Megaptera novaeangliae) were the most common whale species and Pacific white-sided dolphins (Lagenorhynchus obliquidens) were the most common delphinid. Abundance estimates for most species during 2005 were comparable to estimates from a similar coast-wide survey in 2001. Blue whales have been less abundant along the U.S. West Coast in 2001 and 2005 than during the 1990s, whereas estimated humpback whale abundance is greater than during all previous assessments through 2002. The additional survey coverage within the NMS allowed an evaluation of the significance of these regions to cetaceans, and NMS waters clearly represent important habitat for several cetacean species.