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Resident Harbor Seals (Phoca vitulina) in Iliamna Lake, Alaska: Summer Diet and Partial Consumption of Adult Sockeye Salmon (Oncorhynchus nerka)
Abstract: This study assessed the summer diet and consumption patterns of harbor seals (Phoca vitulina) resident in Iliamna Lake, Alaska. The authors predicted that adult sockeye salmon (Oncorhynchus nerka), a seasonally abundant and nutrient-rich prey source, would dominate diets when available and that seals would preferentially consume the most energetically profitable portion of salmon carcasses. Diet was examined by identifying hard parts of prey found in harbor seal scats, and consumption patterns were measured by collecting carcasses of harbor seal-killed sockeye salmon along island spawning grounds. Salmonids were present in 98% of scats that contained identifiable prey, followed by petromyzontids, osmerids, cottids, coregonids, and gasterosterids. The carcass surveys provided evidence of selective consumption patterns of sockeye salmon body parts. Harbor seals consumed the bodies of nearly all (96.6%) male salmon collected, leaving little but the head. In contrast, the belly and eggs were consumed in 63.6% of the female samples, and the entire body was eaten in only 31.3% of females. The harbor seals in Iliamna Lake thus took advantage of the seasonally abundant adult sockeye salmon by consuming them selectively and as a high proportion of their diet, but they also consumed smaller resident fishes, which presumably sustain them during the rest of the year.
Key Words: freshwater harbor seal, Phoca vitulina, sockeye salmon, Oncorhynchus nerka, Iliamna Lake, scat analysis, seasonal prey, selective predation, consumption patterns
Document Type: Research article
Page Numbers: 303-309