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Multicentury Perspective Assessing the Sustainability of the Historical Harvest of Seaducks

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Multicentury Perspective Assessing the Sustainability of the Historical Harvest of Seaducks Multicentury perspective assessing the sustainability of the historical harvest of seaducks Kathryn E. Hargana,1, H. Grant Gilchristb, Nikolas M. T. Clydeb,c, Samuel A. Iversonb,d, Mark R. Forbesc, Linda E. Kimpea, Mark L. Mallorye, Neal Micheluttif, John P. Smolf, and Jules M. Blaisa,1 aDepartment of Biology, University of Ottawa, Ottawa, ON K1N 6N5, Canada; bWildlife Research Division, Science and Technology Branch, Environment and Climate Change Canada, Ottawa, ON K1S 5B6, Canada; cDepartment of Biology, Carleton University, Ottawa, ON K1S 5B6, Canada; dCanadian Wildlife Service, Environment and Climate Change Canada, Gatineau, QC K1A 0H3, Canada; eDepartment of Biology, Acadia University, Wolfville, NS B4P 2R6, Canada; and fPaleoecological Environmental Assessment and Research Laboratory, Department of Biology, Queen’s University, Kingston, ON K7L 3N6, Canada Edited by Rick Battarbee, University College London, United Kingdom, and accepted by Editorial Board Member David W. Schindler March 1, 2019 (received for review August 14, 2018) Where available, census data on seabirds often do not extend trends through time. Furthermore, this proxy can be corrobo- beyond a few years or decades, challenging our ability to identify rated with stable nitrogen isotopes, an already established tool drivers of population change and to develop conservation policies. in assessing seabird-derived nitrogen release to coastal environ- Here, we reconstruct long-term population dynamics of northern ments, both spatially and temporally (1, 4). common eiders (Somateria mollissima borealis). We analyzed sterols Here, we apply biomarker methods available to paleolimnol- together with stable nitrogen isotopes in dated pond sediment cores ogists to assess long-term population trends of northern common to show that eiders underwent broadscale population declines eiders (Somateria mollissima borealis) at nesting colonies in the over the 20th century at Canadian subarctic breeding sites. Likely, eastern Canadian Arctic. We examine changes in δ15N, as well as a rapidly growing Greenland population, combined with reloca- sterols and stanols, in dated sediment records from ponds on tion of Inuit to larger Arctic communities and associated increases nesting islands, as an index to reconstruct colony occupancy of in the availability of firearms and motors during the early to mid- eiders through centuries. In contrast to other studies, which have 20th century, generated more efficient hunting practices, which in often focused on one colony location (5, 9), we present data from SCIENCES turn reduced the number of adult eiders breeding at Canadian many island colonies distributed across a large geographic range ENVIRONMENTAL nesting islands. Our paleolimnological approach highlights that in Hudson Strait, Nunavut—the core of the Arctic eider breed- current and local monitoring windows for many sensitive seabird ing range (10). At these same island colonies, there is significant species may be inadequate for making key conservation decisions. δ15N enrichment in moss and soil samples compared with non- colony islands and mainland reference sites (11), indicating that biomarkers | paleolimnology | Arctic | seabirds | conservation nutrients originate from a trophically elevated source. The northern common eider is a long-lived seaduck with a SCIENCE circumpolar distribution including Arctic Canada and Greenland he factors that shape population dynamics of wildlife often SUSTAINABILITY Tact over time periods well beyond the scope of retrospective (10). Between 60 and 80% of the eiders breeding in Arctic analyses of available field information such as population surveys Canada are estimated to migrate to southwest Greenland to (1). This is particularly true in remote locations like the Cana- dian Arctic and West Greenland where standardized bird surveys Significance only began in the 1950s and even then occurred rarely with in- complete spatial coverage (2). These remote Arctic locations are The paucity of monitoring data for seabird populations at also experiencing extensive change, and there is a need for in- suitable temporal and spatial scales challenges the develop- formation to assess whether contemporary estimates of species ment of realistic and effective conservation policies. We em- abundance and patterns of fluctuation are disconcerting, or ploy newly developed paleoenvironmental techniques at 10 within the realm of natural variation (3). key subarctic seaduck colonies to reconstruct broadscale pop- New biomarker techniques applied to dated lake sediment cores ulation changes at decadal timescales through the 20th century. have unlocked the opportunity to examine long-term population We show that harvesting practices in southwestern Greenland trends among colonial nesting seabirds and seaducks. Lipophilic and northeastern Canada were unsustainable, timed with the biomarkers identified from bird feces (sterols and stanols), along advent of widespread use of shotguns and outboard motors for with more traditional geochemical biomarkers such as stable ni- hunting across the North. Our historical population reconstruc- trogen isotopes (δ15N) preserved in pond sediments, allow for a tions, corroborated with two independent proxies (sterols and multiproxy reconstruction of population changes from sedimen- stable nitrogen isotopes), reaffirms that hunting restrictions were tary records over decades to centuries (4, 5). This is because nu- necessary to prevent the collapse of this subspecies. trient flow from bird guano and related deposition is dynamic and reflects the number of birds present or absent as nesting pop- Author contributions: K.E.H., H.G.G., and J.M.B. designed research; K.E.H., H.G.G., ulations change over time (4, 6). Sterols and stanols, found in N.M.T.C., S.A.I., L.E.K., M.L.M., N.M., J.P.S., and J.M.B. performed research; K.E.H. and J.M.B. contributed new reagents/analytic tools; K.E.H., H.G.G., N.M.T.C., S.A.I., M.R.F., varying concentrations and combinations in the feces of animals L.E.K., M.L.M., N.M., J.P.S., and J.M.B. analyzed data; and K.E.H. wrote the paper. (7), are emerging as important proxies to directly track animal The authors declare no conflict of interest. inputs to lake sediments over decadal-scale and century-scale time This article is a PNAS Direct Submission. R.B. is a guest editor invited by the periods (1, 8). For example, the ratio of cholesterol (cholest-5-en- Editorial Board. β β 3 -ol) to cholesterol and sitosterol ( -sitosterol), a common phy- This open access article is distributed under Creative Commons Attribution-NonCommercial- tosterol, demonstrated significant enrichment of cholesterol in pond NoDerivatives License 4.0 (CC BY-NC-ND). sediments closest to a nesting colony of northern fulmars (Fulmarus 1To whom correspondence may be addressed. Email: [email protected] or jules. glacialis) in the High Arctic and was significantly correlated with [email protected]. 15 ornithogenic δ N enrichment of sediment (9). This “seabird ste- This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. rol index” provides a direct measure of seabird presence and, 1073/pnas.1814057116/-/DCSupplemental. when measured in sediment cores, can be used to infer population www.pnas.org/cgi/doi/10.1073/pnas.1814057116 PNAS Latest Articles | 1of6 Downloaded by guest on September 29, 2021 overwinter (12, 13) (Fig. 1A). Reports suggest that there were Eider Pond sediment record, which may be due to the higher tro- once millions of eiders in the Greenland–Canada region (14), but phic level of Arctic terns relative to common eiders (18). numbers were substantially reduced by the late 20th century (15– Overall, across all study islands, eiders use freshwater ponds 17). Eider breeding colonies are remote, often difficult to access, to drink during summertime incubation (10), and a positive re- and can have high interannual variation in occupancy, so only sparse lationship exists between breeding success and distance to the nest count records exist. To supplement these records, we employed nearest pond (19, 20). Thus, islands supporting ponds are at- a comprehensive spatial paleolimnological study of one colony in tractive breeding sites, and nesting eiders are observed concen- trated around an island’s main pond such that vegetation the Canadian High Arctic, “Tern Island” (Fig. 1A), with no local coverage and soil depth are greatest around an island’s pond and hunting; three nesting islands in Digges Sound, Hudson Strait ∼ decrease with increasing distance from pond margins (11). Once southwest of the community of Ivujivik ( 370 people) with low-to- female eiders reach these breeding grounds (displaying high moderate local hunting pressure; and six nesting islands southeast of philopatry) and commence incubation, they remain on the nest the community of Cape Dorset in Hudson Strait (∼1,450 people) 99.8% of the time (21), losing ∼45% of their body mass over with high local hunting pressure (Fig. 1B). These islands do not ∼24 d (22). Waste products released from the nesting colonies support large numbers of other bird species because they are flat, become archived in pond sediments, which serve as historical and most marine birds nest on cliffs, whereas eiders are the pre- records of seaduck densities on the island (1, 23). dominant ground-nesting marine bird in the Canadian Arctic. Tern Island (75°49′ N, 96°20) is distinguished from the other islands due Results 210 to its remote location in the High Arctic and inaccessibility by sea Sediment Chronologies for Dated Cores. Profiles of the Pb ac- canoe. At this site, a unique set of circumstances has led to the tivity trends for sediment cores CD135, CD044, and CD056 followed a classic exponential decline with increasing depth, with segregation of Arctic tern (Sterna paradisaea) and eider colonies into 210 ∼ separate drainage basins of two ponds (∼1kmapart),whichhave highest initial Pb activity levels measured in CD044 ( 1,000 Bq/kg) (SI Appendix,Fig.S1). Several of the sediment cores (CD045, distinct water chemistry and sediment geochemistry reflecting the CD114) showed greater fluctuation in initial 210Pb activity seabird nesting in its catchment (18).
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