13 
Abstract — Harbor seals (Phoca 
vitulina) are an abundant preda- 
tor along the west coast of North 
America, and there is considerable 
interest in their diet composition, 
especially in regard to predation on 
valued fish stocks. Available infor- 
mation on harbor seal diets, primar- 
ily derived from scat analysis, sug- 
gests that adult salmon ( Oncorhyn - 
chus spp.), Pacific Herring (Clupea 
pallasii ), and gadids predominate. 
Because diet assessments based on 
scat analysis may be biased, we in- 
vestigated diet composition through 
quantitative analysis of fatty acid 
signatures. Blubber samples from 
49 harbor seals captured in west- 
ern North America from haul-outs 
within the area of the San Juan Is- 
lands and southern Strait of Georgia 
in the Salish Sea were analyzed for 
fatty acid composition, along with 
269 fish and squid specimens rep- 
resenting 27 potential prey classes. 
Diet estimates varied spatially, de- 
mographicaily, and among individual 
harbor seals. Findings confirmed the 
prevalence of previously identified 
prey species in harbor seal diets, but 
other species also contributed sig- 
nificantly. In particular. Black ( Se - 
bastes melanops) and Yellowtail (S. 
flauidus) Rockfish were estimated to 
compose up to 50% of some individu- 
al seal diets. Specialization and high 
predation rates on Black and Yellow- 
tail Rockfish by a subset of harbor 
seals may play a role in the popu- 
lation dynamics of these regional 
rockfish stocks that is greater than 
previously realized. 
Manuscript submitted 31 January 2012. 
Manuscript accepted 31 October 2012. 
Fish. Bull. 111:13-26 (2013). 
doi:10.7755/FB.111.1.2 
The views and opinions expressed 
or implied in this article are those of the 
author (or authors) and do not necessar- 
ily reflect the position of the National 
Marine Fisheries Service, NOAA. 
New insights into the diets of harbor seals 
(Phoca vitulina) in the Salish Sea revealed by 
analysis of fatty acid signatures 
Jeffrey F. Bromaghin (contact author)’ 
Monique M. Lance 2 
Elizabeth W. Elliott 3 
Steven J. Jeffries 2 
Alejandro Acevedo-Gutierrez 4 
John M. Kennish 3 
Email address for contact author: |bromaghin@usgs gov 
U. S. Geological Survey 
Alaska Science Center 
4210 University Drive 
Anchorage, Alaska 99508 
Washington Department of Fish & Wildlife 
Wildlife Research Division 
7801 Phillips Road SW 
Lakewood, Washington 98498 
3 Department of Chemistry and Applied 
Sciences, Engineering and 
Technology (ASED Laboratory 
University of Alaska Anchorage 
3211 Providence Drive 
Anchorage, Alaska 99508 
4 Department of Biology 
Western Washington University 
516 High St MS 9160 
Bellingham, Washington 98225-9160 
The harbor seal (Phoca vitulina) is 
the most abundant pinniped spe- 
cies in the protected coastal waters 
of Washington State and British 
Columbia, Canada (Jeffries et ah, 
2003). This species is a generalist 
piscivorous predator, at or near the 
apex of marine food webs. Such large 
and mobile endothermic predators 
require high caloric intake to support 
growth, reproduction, and foraging 
activity (e.g., Williams et ah, 2004). 
Given their abundance and trophic 
position, harbor seals undoubtedly 
make up an influential component 
of their marine ecosystems (Sergio 
et ah, 2006; Heithaus et ah, 2008; 
Schmitz et ah, 2010). 
Numerous fish stocks of historic 
commercial importance are depressed 
or have declined significantly in the 
Salish Sea of western North Amer- 
ica, including Pacific Herring (Clu- 
pea pallasii), Chinook Salmon ( On - 
corhynchus tshawytscha) in Puget 
Sound, Steelhead Trout ( O . mykiss), 
Pacific Hake ( Merluccius productus ), 
Walleye Pollock (Theragra chalco- 
gramma), and many species of rock- 
fish ( Sebastes spp.) (Federal Register, 
2007). Under the Endangered Species 
Act, the Puget Sound and Georgia 
Basin distinct population segments 
of Yelloweye (S. ruberrimus) and Ca- 
nary (S. pinniger) Rockfish recently 
were listed as threatened, and Bo- 
caccio (S. paucispinis) was listed as 
endangered (Federal Register, 2010). 
Three additional rockfish species — 
Brown Rockfish (S. auriculatus). Cop- 
per Rockfish (S. caurinus), and Quill- 
back Rockfish (S. maliger ) — now are 
considered federal species of concern, 
and the remaining 7 species found in 
the Salish Sea are listed as species 
of concern by the State of Washing- 
ton (M. Lance, personal commun.). 
Continued declines in fish abundance 
and the failure of depleted popula- 
tions to recover have elevated con- 
cerns among fishing crews, manag- 
ers, and conservationists (Musick et 
ah, 2001; Williams et ah, 2010). 
The concurrence of abundant har- 
bor seals and depressed fish popula- 
tions has stimulated debate about 
the degree to which harbor seals may 
regulate prey abundance (Orr et ah, 
2004). Numerous factors may have 
contributed to the declines in fish 
