Paper: Food habits of harbor seals (Phoca vitulina) in two estuaries in the central Salish Sea
This paper discusses the dietary habits of harbor seals (Phoca vitulina) in two estuaries in Puget Sound.
Harbor seals are the most common pinniped species in the Salish Sea, and they have historically been blamed for declines in commercial fisheries. The State of Washington financed a bounty program from 1943 to 1960, but the closure of the program and the enactment of the Marine Mammal Protection Act led to a seven- to ten-fold increase in the harbor seal population in Washington. Harbor seal predation has been identified as a contributor to the decline of Pacific herring, Pacific hake, and walleye pollock, as well as juvenile and adult salmonids. Several studies have looked at the diet of seals in non-estuarine haulout sites, but few have examined their dietary habits in soft-bottomed estuarine environments.
Understanding harbor seal diets is an important component of tracking their impact on fish populations. In this study, researchers analyzed scat samples from seals at haulout sites in Padilla Bay and Drayton Harbor. They found that the total number of taxa consumed by seals at each site was comparable to studies of other locations in the Salish Sea, but the diet richness was one of the highest found for harbor seals in any habitat, which likely reflects the prey available in an estuarine environment as well as the opportunistic foraging habits of seals. The study was also the first to find evidence of harbor seals preying on small mammals. The results show that seals mostly forage in and around the estuaries during spring, summer, and fall, and consume prey from over two dozen taxonomic families. Further study could help to identify the impact of harbor seal predation on prey species.
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