27 
Fish consumption by harbor seals (Phoca 
vitulina) in the San Juan Islands, Washington 
Email address for contact author: sarah_howard@nps gov 
Abstract — The harbor seal ( Phoca 
vitulina) is a large-bodied and abun- 
dant predator in the Salish Sea 
ecosystem, and its population has 
recovered since the 1970s after pas- 
sage of the Marine Mammal Protec- 
tion Act and the cessation of boun- 
ties. Little is known about how this 
large predator population may affect 
the recovery of fish stocks in the 
Salish Sea, where candidate marine 
protected areas are being proposed. 
We used a bioenergetics model to 
calculate baseline consumption rates 
in the San Juan Islands, Washing- 
ton. Salmonids ( Oncorhynchus spp.) 
and herring (Clupeidae) were the 2 
most energetically important prey 
groups for biomass consumed by 
harbor seals. Estimated consumption 
of salmonids was 783 (±380 standard 
deviation [SD ] ) metric tons (t) in 
the breeding season and 675 (±388 
SD t in the nonbreeding season. 
Estimated consumption of herring 
was 646 (±303 SD) t in the breeding 
season and 2151 (±706 SD) t in the 
nonbreeding season. Rockfish, a de- 
pressed fish stock currently in need 
of population recovery, composed one 
of the minor prey groups consumed 
by harbor seals (84 [±26 SD| t in the 
nonbreeding season). The variables 
of seal body mass and proportion of 
prey in seal diet explained >80% of 
the total variation in model outputs. 
Prey groups, such as rockfish, that 
are targeted for recovery may still 
be affected by even low levels of 
predation. This study highlights the 
importance of salmonids and herring 
for the seal population and provides 
a framework for refining consump- 
tion estimates and their confidence 
intervals with future data. 
Manuscript submitted: 4 November 2011. 
Manuscript accepted 31 October 2012. 
Fish. Bull. 111:27-41 (2013). 
doi: 10. 7755/FB. 111.1.3 
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. 
Sarah M. S. Howard (contact author ) 1 
Monique M. Lance 2 
Steven J. Jeffries 2 
Alejandro Acevedo-Gutierrez 1 
1 Biology Department 
Western Washington University 
516 High Street 
Bellingham, Washington 98225 
Present address: National Park Service 
10 Organ Pipe Drive 
A|o, Arizona 85321 
2 Washington Department of Fish & Wildlife 
7801 Phillips Road SW 
Lakewood, Washington 98498 
Overfishing and habitat change have 
affected fish populations heavily 
in the inland waters of the Pacific 
Northwest. Many formerly abundant 
fish species are now species of con- 
servation concern, including ground- 
fish stocks, such as rockfish species 
( Sebastes spp.) and Pacific Hake 
(Merluccius productus), forage fish 
stocks such as Pacific Herring (Clu- 
pea pallasii), and several salmonid 
species ( Oncorhynchus spp.) (Musick 
et ah, 2000; Mills and Rawson, 2004). 
Most recently, 3 rockfish species (S. 
ruberrimus, S. pinniger, S. paucispi- 
nis) were listed under the Endan- 
gered Species Act as threatened or 
endangered in Puget Sound, Wash- 
ington State (Federal Register, 2010). 
The decline of all these popula- 
tions, which perform a critical func- 
tion in regional food webs (Simenstad 
et al., 1979; Schindler et al., 2003) 
and have commercial and recre- 
ational value, has created a need for 
recovery strategies at the ecosystem 
level. Fish recovery efforts currently 
rely on traditional fisheries manage- 
ment approaches, such as reduction 
of fishing pressure and creation of 
no-take refuges or marine reserves, 
and on habitat restoration (Allison et 
al., 1998; Roni et al., 2002). Marine 
reserves in particular are more like- 
ly to be successful for species, such 
as rockfish, that have small home 
ranges and high site fidelity (Love 
et al., 2002), and reserves are impor- 
tant management tools for recovery 
of rockfish in the Pacific (Murray et 
al., 1999). More reserves have been 
proposed recently for the San Juan 
Islands, 1 an island group that is part 
of the Salish Sea marine ecosystem 
that spans U.S. and Canadian waters 
(Fig. 1). For pelagic species, such as 
salmonids and forage fishes, recovery 
efforts call for habitat protection and 
mitigation of water-pollution issues, 
among other factors, as management 
tools (Fluharty, 2000; Schindler et 
al., 2003). 
The restoration of predators in ma- 
rine ecosystems can reestablish tro- 
phic relations and restructure habi- 
1 McConnell, M. L., and P. A. Dinnel. 2002. 
Rocky reef bottomfish recovery in Skagit 
County. Phase II final report: assessment 
of eight potential marine reserve sites 
& final site recommendations. Skagit 
County Marine Resources Committee, 
Mount Vernon, WA, 43 p. [Available 
from http://www.nwstraits.org/Archives/ 
Library.aspx.] 
