- Patterns of seasonal abundance of harbor seals at Netarts and Tillamook Bays, Oregon, were documented by recording numbers of seals hauling out on tidally exposed sand flats in both bays. Harbor seal abundance at Tillamook Bay peaked during pupping (May-June) and molting (August) periods, while peak abundance at Netarts Bay coincided with the annual return (October-November) of chum salmon, Oncorhynchus keta, to a hatchery on Whiskey Creek Observations of seals preying on adult salmon resulted in estimated losses of 6.1, 7.2, and 1.5% of the total chum returns for 1978, 1979, and 1980, respectively, due to seal predation in the Whiskey Creek area. Other prey species of harbor seals at Netarts Bay were identified by the recovery of prey hard parts from seal feces collected on haul-out areas. The Pacific sand lance, Ammodytes hexapterus, was the most frequently identified prey item. Ten species of flatfish (Order Pleuronectiformes) were identified as harbor seal prey with five species (Parophrys uetulus, Glyptocephalus zachirus, Citharichthys sor-didus,Microstomuspacificus, andLyopsetta exilis) ranking among the seven most frequently occurring food items. In general, benthic and epibenthic fish appeared to be important in the harbor seal diet. Distributions, abundances, and estimated sizes of identified prey species indicated that harbor seals had fed both in Netarts Bay and in the nearshore ocean. Movements of radio-tagged harbor seals between Netarts Bay and Tillamook Bey were common (45.4% of tagged seals made at least one move between bays). Tagged harbor seals frequented at least four different estuaries and one coastal haul-out area, ranging from 25 to 550 km from the tagging area.