Food Habits of Harbor Seals (Phoca vitulina) in Two Estuaries in the Central Salish Sea

Abstract

This study describes the seasonal diet composition of the Pacific harbor seal (Phoca vitulina) in two estuaries, Padilla Bay and Drayton Harbor, in the central Salish Sea. Prey remains were recovered from harbor seal fecal samples (scats) collected at haul-out sites during spring and summer/ fall in 2006. Top prey taxa (≥ 25% frequency of occurrence) were compared between seasons, estuaries, and between estuarine and non-estuarine haul-out sites. Overall, prey from at least 26 taxonomic families were identified in 198 harbor seal scats. In Padilla Bay, the most common prey were gunnel (family Pholidae; 88.6%), snake prickleback (Lumpenus sagitta; 59.1%), Pacific staghorn sculpin (Leptocottus armatus; 50.0%), and shiner perch (Cymatogaster aggregata; 47.7%). Threespine stickleback (Gasterosteus aculeatus; 95.5%) and Pacific herring (Clupea pallasi; 83.1%) were the most frequently consumed species in Drayton Harbor; shiner perch, snake prickleback, mammal, and Pacific staghorn sculpin also each occurred in ≥ 50% of samples from at least one season. Occurrences of top prey taxa varied by season, estuary, and habitat type. Diet composition suggests that harbor seals in Padilla Bay and Drayton Harbor foraged primarily within estuarine habitats such as those found near the haul-out sites. Temporal and spatial variations in diet appeared to reflect differences in the availability of prey taxa. This study also identifies mammals as a potentially novel prey item for harbor seals in Drayton Harbor.

New insights into the diets of harbor seals (Phoca vitulina) in the Salish Sea revealed by analysis of fatty acid signatures

“…We surmise that such temporal heterogeneity exists, but that evidence of these seasonally available prey species in harbor seal blubber was diminished by late October. The lack of summer seal samples may partially explain the difference between these results and assessments of harbor seal diet based on scats, in which salmon species and Pacifi c Herring are prevalent (Luxa, 2008;Lance et al, 2012). A complete assessment of seasonal variation in harbor seal diets would require a somewhat expanded investigation, in which the distribution of sampling effort would be designed to investigate potential changes in diet expected on the basis of seasonally predictable shifts in the availability of prey species.…”

Short Note: Inferences on the Diet of the Eastern Pacific Harbor Seal (Phoca vitulina richardii) at the Southern End of Its Distribution: Stable Isotopes and Scats Analyses

“…The identified prey in our work differ from other studies of P. v. richardii from other latitudes. There are other important prey reported for harbor seals in California, Washington, and Alaska such as the yellowfin goby (Acanthogobius flavimanus), shiner surfperch (Cymatogaster aggregate), Pacific staghorn sculpin (Leptocottuss armatus), Pacific sand lance (Ammodytes hexapterus), coho salmon (Oncorhynchus kisutch), pollock (Theragra calcograma), capelin (Mallatus villosus), cephalopods (squids and octopus), and crustaceans, among other species (Pitcher, 1980;Gibble, 2011;Luxa & Acevedo-Gutiérrez, 2013). These and other studies, as well as ours, report a diet dominated by fish prey; we also report a high frequency of an octopus prey, an item that is present in the Phoca's diet from regions like the Gulf of Alaska (Pitcher, 1980).…”

Diet composition and biomass consumption of harbour seals in Telemark and Aust-Agder, Norwegian Skagerrak

“…They inhabit coastal areas around the northern Pacific and Atlantic oceans (Teilmann and Galatius 2018). Between foraging trips harbour seals return to specific haul-out sites to socialize and rest with conspecifics, a behaviour called central place foraging (Geiger et al 2013;Luxa and Acevedo-Gutiérrez 2013). Generally, seals spend most of their time hauled out during daytime and low tide, while most foraging trips take place at night (Thompson et al 1989;Thompson and Miller 1990;Bjørge et al 1995;Ramasco et al 2014).…”

“…clupeoids, gadoids, sandeels (Ammodytidae), sculpins and flatfish (e.g. Tollit and Thompson 1996;Bromaghin et al 2012;Lance et al 2012;Geiger et al 2013;Luxa and Acevedo-Gutiérrez 2013). They vary their diets according to season and geographical location, seemingly to prefer the regionally and seasonally most abundant of both benthic and pelagic species (e.g.…”