Bromaghm et al: Diets of Phoca vitulina in the Salish Sea revealed by analysis of fatty acid signatures 
21 
diet composition of 0.0% for Black and Yellowtail Rock- 
fish, and estimates for the remaining 14 males ranged 
from 8.2% to 51.4% and averaged 31.8%. Although fe- 
males were more consistent in their reliance on Shiner 
Perch, the estimated contribution of Black and Yellow- 
tail Rockfish exceeded 25% for 3 individuals. There 
were no discernible patterns in the capture location 
or date with respect to the magnitude of rockfish 
estimates for either males or fe- 
males, a result that is consistent 
with the nonsignificant interaction 
between location and gender in the 
linear model. One female seal was 
captured twice, at Padilla Bay in 
spring 2007 and at Vendovi Island 
in winter 2008. The diet composi- 
tion of this female was estimated to 
be -90% Shiner Perch and -9% Chi- 
nook Salmon, with negligible contri- 
butions from other prey classes, on 
both occasions. 
Discussion 
Our findings re-affirm the impor- 
tance of several commercially impor- 
tant fish species to harbor seal diets, 
particularly salmon species, Pacific 
Herring, and Shiner Perch, reported 
by prior investigators (Scheffer and 
Slipp, 1944; Everitt et al., 1981; 
Brown and Mate, 1983; Olesiuk, 
1993; Zamon, 2001; Orr et al., 2004; 
Wright et al., 2007; Thomas et al., 
2011; Lance et al., 2012). However, 
our results also reveal that rockfish 
species contribute more substan- 
tially to harbor seal diets than has 
been recognized previously, exceed- 
ing 10% of the average diet of all 
harbor seals combined. Given that 
QFASA estimates are thought to 
describe diets integrated over a pe- 
riod of weeks to months (Iverson et 
al., 2004; Budge et al., 2006), esti- 
mates of this magnitude may reflect 
substantial periodic (and, perhaps, 
sustained) predation on species of 
rockfish. Although quantitative esti- 
mates of rockfish abundance are un- 
available, rockfish populations are 
considered depressed and, given the 
regional abundance of harbor seals 
(Jeffries et al., 2003), the predation 
rates indicated by these findings 
may be sufficiently high to influ- 
ence their population dynamics, on 
a local or, perhaps, regional scale. 
Consequently, management plans 
to enhance rockfish abundance may 
need to give greater consideration to 
the potential influence of pinniped 
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Prey group 
Figure 4 
Mean diet composition estimates for harbor seals ( Phoca vitulina) in the 
Salish Sea, unadjusted for differential fat mass among prey classes, by 
sex: (A) females and (B) males. Error bars are ±1 standard error of the 
estimate. Prey classes are defined as B&YR (Black \Sebastes melanops ] 
and Yellowtail [S. flavidus] Rockfish), CR (Copper Rockfish (S. caurinus]), 
PSR (Puget Sound Rockfish [S. emphaeus]), Chin (mature Chinook Salm- 
on [ Oncorhynchus tshawytscha ]), Chum (mature Chum Salmon 10. beta]), 
Coho (mature Coho Salmon 10. kisutch)), Sock (mature Sockeye Salmon 
10. nerka]). Pink (mature Pink Salmon [O. gorbuscha]), Sal-M (medium- 
size Chinook and Coho Salmon), Sal-S (small Chinook, Chum, sockeye, and 
Pink Salmon), Pol (Walleye Pollock [ Theragra chalcogramma )), Her (Pacific 
Herring \Clupea pallasii ] at least 2 years old), YH&SL (Pacific Herring 
less than 2 years old and Pacific Sand Lance [Ammodytes hexapterus ]), NA 
(Northern Anchovy \Engraulis mordax]), SP (Shiner Perch I Cymatogaster 
aggregata]), PM (Plainfin Midshipman [Porichthys notatus]), SD (Spiny 
Dogfish [Squalus acanthias]), OIS (Opalescent Inshore Squid [ Loligo opal- 
escens]), G&S&F (Kelp Greenling [ Hexagrammos decagrammus]. Pacific 
Staghorn Sculpin [Leptocottus armatus ], and Starry Flounder [Platichthys 
stellatus]). 
