shifting baseline of northern fur seal ecology in the northeast Pacific Ocean

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 104; no. 23; pp. 9709 - 9714
• Main Authors: Newsome, Seth D, Etnier, Michael A, Gifford-Gonzalez, Diane, Phillips, Donald L, van Tuinen, Marcel, Hadly, Elizabeth A, Costa, Daniel P, Kennett, Douglas J, Guilderson, Tom P, Koch, Paul L
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 05-06-2007; National Acad Sciences
• Subjects: Age Determination by Skeleton; Age structure; Analysis of Variance; Animal populations; Animal reproduction; Animals; Archaeological sites; Archaeology; Base Sequence; Biological Sciences; Bone and Bones - chemistry; Bones; Breeding; Callorhinus ursinus; Carbon Isotopes - analysis; Climate; Cluster Analysis; Collagen - analysis; Conservation of Natural Resources; Demography; DNA Primers; Ecology; Extinction, Biological; Fossils; Fur Seals - physiology; Geography; Isotopes; Likelihood Functions; Marine; Marine ecology; Marine mammals; Models, Genetic; Molecular Sequence Data; Nitrogen Isotopes - analysis; Pacific Ocean; Phylogeny; Physical Sciences; Pinnipedia; Population Dynamics; Population ecology; Pups; Radiocarbon; Reproduction - physiology; Seals; Seas; Sequence Analysis, DNA; Pacific Ocean; California; Pacific Northwest; INE, USA, Pacific Northwest; INE, USA, California; IN, USA, Alaska, Aleutian Is
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0610986104

Historical data provide a baseline against which to judge the significance of recent ecological shifts and guide conservation strategies, especially for species decimated by pre-20th century harvesting. Northern fur seals (NFS; Callorhinus ursinus) are a common pinniped species in archaeological sites from southern California to the Aleutian Islands, yet today they breed almost exclusively on offshore islands at high latitudes. Harvest profiles from archaeological sites contain many unweaned pups, confirming the presence of temperate-latitude breeding colonies in California, the Pacific Northwest, and the eastern Aleutian Islands. Isotopic results suggest that prehistoric NFS fed offshore across their entire range, that California populations were distinct from populations to the north, and that populations breeding at temperate latitudes in the past used a different reproductive strategy than modern populations. The extinction of temperate-latitude breeding populations was asynchronous geographically. In southern California, the Pacific Northwest, and the eastern Aleutians, NFS remained abundant in the archaeological record up to the historical period [almost equal to]200 years B.P.; thus their regional collapse is plausibly attributed to historical hunting or some other anthropogenic ecosystem disturbance. In contrast, NFS populations in central and northern California collapsed at [almost equal to]800 years B.P., long before European contact. The relative roles of human hunting versus climatic factors in explaining this ecological shift are unclear, as more paleoclimate information is needed from the coastal zone.