Graduate Research Assistant - Katie Luxa
NOAA/Padilla Bay NERR Research Assistantship Recipient
Harbor Seal Diet
Katie Luxa
M.S Candidate, Western Washington University
Department of Biology
Bellingham, WA
The diet of harbor seals Phoca vitulina in southern Padilla Bay, Washington
Background
In the last decade, several marine protected areas (MPAs) have been established in Puget Sound to
aid the recovery of depleted bottomfish populations, primarily rockfish (Sebastes spp.), but also
lingcod (Ophiodon elongatus), greenlings (Hexagrammidae spp.), and cabezon (Scorpaenichthys
marmoratus). Exploited species inside MPAs exhibit increased abundance, average size, and biomass
over a relatively short period of time and there is further evidence that MPAs enhance adjacent fisheries.
In response to this recovery, however, it is possible that marine predators may increase their abundance and
foraging activity in MPAs, hindering further prey recovery. The foraging habits of predators must be understood
in order to predict their potential effect on recovering fish stocks in marine protected areas.
The harbor seal (Phoca vitulina) is the most abundant pinniped species in Washington and an important marine predator. Harbor seals are opportunistic predators that feed on a wide variety of prey. Dominant prey types tend to vary geographically, seasonally, and inter-annually. Diets are thus assumed to reflect the unique prey assemblages available spatially and temporally, with the most abundant species composing a majority of the diet, although energy content may also influence prey selection. For this reason, harbor seals are often considered a threat to local fisheries and could potentially threaten recovering fish stocks in marine protected areas.
The study will aim to: 1) describe the relative abundance of each prey species in the diet of harbor seals in southern Padilla Bay, 2) examine temporal variation in seal diet by comparing seasons, and 3) compare the primary prey species of harbor seals from soft-bottom (southern Padilla Bay) versus rocky (San Juan Islands) haul-out sites.
Method
Fecal samples will be collected from seal haul-out sites every 10-14 days via kayak within seasons winter/spring
and summer/fall to assess diet composition. The number of seals and age classes present at each site will be estimated
and recorded prior to sample collection. Prey parts will be examined and identified to the lowest possible taxonomic
level and used to calculate the minimum number of individuals, percent frequency of occurrence, and percent relative
abundance, which will be used for seasonal comparisons of diet composition.
Significance to Padilla Bay
This study will provide baseline data on the seasonal diet composition of a top marine predator, the Pacific harbor
seal, in northern Puget Sound, Washington. The results will also be compared to a concurrent study of harbor seal diet
in the San Juan Islands, a rocky substrate region. This comparison will provide a broader understanding of harbor seal
diet in northern Puget Sound and the potential impact that these predators may have on prey populations.
Biographical Information
Fig. 1. Katie Luxa collecting samples at seal haul-out sites via Kayak.
Katie Luxa is currently a graduate student in the Biology Department at Western Washington University (Fig. 1).
Her graduate advisor is Dr. Alejandro Acevedo-Gutierrez. Before enrolling at WWU, Katie received a B.S. in Marine
Science concentration in Marine Vertebrate Biology from Southampton College of Long Island University. Her research
is partially funded by the Padilla Bay Research Assistantship in Estuarine Science and Coastal Zone Management and
the Western Washington University Bureau for Faculty Research.