198 
Abstract— Documenting year-round 
diversity and distribution of marine 
mammals off Southern California is 
important for assessment of effects 
of potentially harmful anthropogenic 
activities. Although the waters off 
Southern California have been sur- 
veyed extensively for marine mam- 
mals over the past 18 years, such 
surveys have been periodic and were 
conducted primarily from summer to 
fall, thereby missing potential sea- 
sonal shifts. We examined seasonal 
abundance and population density 
of cetaceans off Southern Califor- 
nia from 16 shipboard line-transect 
surveys conducted quarterly during 
2004-08. The study area consisted 
of 238,494 km 2 of coastal, shelf, and 
pelagic oceanic habitat from near- 
shore waters to 700 km offshore. 
Based on 693 encounters of 20 ce- 
tacean species, abundance estimates 
by seasonal period (summer-fall or 
winter-spring) and depth (shallow: 
<2000.5 m; deep: >2000.5 m) were 
determined for the 11 most com- 
monly encountered species. The fol- 
lowing are values of uncorrected 
density (individuals/1000 km 2 , coef- 
ficients of variation in parentheses) 
for the seasonal period and depth 
with greatest density for a selec- 
tion of the species in this study: 
blue whale ( Bcilaenoptera musculus ), 
summer-fall, shallow, 3.2 (0.26); fin 
whale (B. physalus), summer-fall, 
shallow, 3.7 (0.30); humpback whale 
( Megaptera novaeangliae), summer- 
fall, shallow, 3.1 (0.36); short-beaked 
common dolphin ( Delphinus del- 
phis), summer-fall, shallow, 1319.7 
(0.24); long-beaked common dolphin 
( D . capensis), summer-fall, shallow, 
687.9 (0.52); and Dali’s porpoise 
( Phocoenoides dalli ), winter-spring, 
deep, 48.65 (0.28). Seasonally, den- 
sity varied significantly by depth for 
humpback whales, fin whales, and 
Pacific white-sided dolphins. 
Manuscript submitted 24 January 2013. 
Manuscript accepted 23 May 2014. 
Fish. Bull. 112:198-220 (2014). 
doi:10.7755/FB.112.2-3.7 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Seasonal distribution and abundance of 
cetaceans off Southern California estimated 
from CalCOFI cruise data from 2004 to 2008 
Annie B. Douglas 1 (contact author) Andrea M. Havron 15 
John Calambokidis 1 Dominique L. Camacho 1 ' 5 
Lisa M. Munger 2 Greg S. Campbell 2 
Melissa S. Soldevilla 3 2 John A. Hildebrand 2 
Megan C. Ferguson 4 
Email address for contact author: abdouglas@cascadiaresearch.org 
1 Cascadia Research Collective 
21814 West Fourth Avenue 
Olympia, Washington 98501 
2 Scripps Institution of Oceanography 
University of California, San Diego 
8635 Discovery Way 
La Jolla, California 92093-0210 
3 Southeast Fisheries Science Center 
National Marine Fisheries Service, NOAA 
75 Virginia Beach Drive 
Miami, Florida 33149 
4 National Marine Mammal Laboratory 
Alaska Fisheries Science Center 
National Marine Fisheries Service, NOAA 
7600 Sand Point Way NE 
Seattle, Washington 98115-6349 
5 Spatial Ecosystems 
P.O. Box 2774 
Olympia, Washington 98507 
At least 30 species of cetaceans are 
found in the California Current 
(Leatherwood et ah, 1982), includ- 
ing 5 species of large whales listed 
as endangered under the U.S. En- 
dangered Species Act. The abun- 
dance and diversity of species along 
the West Coast of the United States 
and the continental slope are closely 
linked to the high level of biological 
production that is caused by upwell- 
ing and mixing of 4 different water 
masses along the California coast 
on a seasonal and interannual basis 
(Reid et ah, 1958; Smith et ah, 1986; 
Munger et ah, 2009). Although these 
waters are important to marine fau- 
na, they are also increasingly impor- 
tant to humans who use them for 
commercial shipping and fishing; oil 
and gas exploration, development, 
and production; naval exercises; 
and recreation. The combined use 
of these highly productive waters 
by cetaceans and humans can lead 
to ships striking large whales (Jen- 
sen and Silber, 2003; Berman-Kow- 
alewski et ah, 2010), entanglements 
of cetaceans in fishing gear (Julian 
and Beeson, 1998; Laist et ah, 2001; 
Carretta et ah, 2011b), and disrup- 
tion of normal behaviors by under- 
water sound (McDonald et ah, 2006; 
Weilgart, 2007). To assess long-term 
impacts of fisheries, industry, and 
ecosystem variability on marine 
mammals, it is necessary to estimate 
abundance, understand stock struc- 
ture, and determine seasonal habitat 
use by the species that inhabit these 
waters. 
Abundance for the summer and 
fall seasons has been estimated for 
many cetacean species in waters off 
California, Oregon, and Washington 
through the use of ship-based line- 
transect surveys or mark-recapture 
techniques of photographically iden- 
tified whales (Calambokidis and Bar- 
low, 2004; Barlow and Forney, 2007; 
Carretta et ah, 2011b). However, 
weather conditions make ship-based 
line-transect surveys difficult to con- 
duct year-round, and few studies have 
quantified habitat and distribution 
shifts of marine mammals during the 
