Bromaghm et al: Diets of Phoca vituhna in the Salish Sea revealed by analysis of fatty acid signatures 
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Map of the San Juan Island region, where samples were collected for our investigation of the diet 
composition of harbor seals ( Phoca vitulina) in the Salish Sea. Harbor seals were captured in the 
vicinity of Padilla Bay, Bird Rocks, Vendovi Island, and the Belle Chain Islets. 
Sampling of predator and prey 
Harbor seals were captured from April 2007 to March 
2008 at 3 sites in the San Juan Islands of Washington 
State and at a fourth site in the adjacent Gulf Islands 
in British Columbia (Fig. 1). Padilla Bay (48°28.37 N, 
122°30.88'W) is characterized by estuarine-mudflat 
habitat, Vendovi Island (48°67.10'N, 122°61.10'W) con- 
sists of rocky reef habitat located in close proximity to 
Bellingham, Samish, and Padilla Bays, and Bird Rocks 
(48°29.16'N, 122°45.61'W) comprises rocky reef habitat 
in Rosario Strait. The fourth site was the Belle Chain 
Islets, a rocky reef in the southeastern Gulf Islands of 
British Columbia (48°49.67'N, 123°11.56'W) with habi- 
tat similar to that of Bird Rocks. 
Forty-nine blubber samples were collected from har- 
bor seals according to standard techniques (Iverson 
et al., 1997; Walton et al., 2000; Walton and Pomeroy, 
2003) under Marine Mammal Protection Act Research 
Permit 782-1702-00. Seals were captured in salmon 
landing nets and physically restrained during process- 
ing following the method of Jeffries et al. (1993). The 
sampling location on the left side of the pelvic region 
was shaved with a razor, rinsed with isopropyl alco- 
hol, scrubbed with Betadine, and rinsed again with 
isopropyl alcohol. A complete cross section of blubber 
from skin to muscle was collected with a sterile, 6-mm 
biopsy punch. A full cross-section sample provides the 
most complete information regarding diet because pho- 
cid blubber is not homogenous throughout its depth 
and the inner layer responds most quickly to diet shifts 
(Iverson et al., 1997). The biopsy site was then filled 
with antiseptic cream and left open to drain. Each sam- 
ple was placed immediately in chloroform with 0.01% 
butylated hydroxytoluene to inhibit oxidation in glass 
vials with Teflon lids, placed on ice while in the field, 
and subsequently stored frozen at -80°C until analysis. 
Seal samples were associated with these covariates: 
sampling location, sex, and season (Table 1). Seasons 
were defined as spring (March to May), fall (October to 
November), and winter (December to February). 
We sampled fish and cephalopod species known to 
be consumed by harbor seals in the San Juan Islands 
region on the basis of previous fecal analyses (Lance et 
al., 2012). Some adult salmon samples were obtained 
from seafood processors and staff of the NOAA North- 
west Fisheries Science Center. Other prey were cap- 
tured from throughout the study area between June 
