STP1219: Common Murre Abundance, Phenology, and Productivity on the Barren Islands, Alaska: The Exxon Valdez Oil Spill and Long-Term Environmental Change

    Boersma, PD
    Professor, Institute for Environmental Studies and Department of Zoology, University of Washington, Seattle, WA

    Parrish, JK
    Research Associate, and Technician, Institute for Environmental Studies, University of Washington, Seattle, WA

    Kettle, AB
    Research Associate, and Technician, Institute for Environmental Studies, University of Washington, Seattle, WA

    Pages: 34    Published: Jan 1995


    Abstract

    The Exxon Valdez oil spill in 1989 caused substantial seabird mortality. By 1 August, more than 30 000 seabird carcasses (74% murres) were recovered, and it was initially estimated that between 100 000 and 300 000 seabirds were killed. The Barren Islands, in particular East Amatuli Island, support the largest seabird colonies within the path of the spill. With respect to murres nesting on the Barren Islands, claims were made that the population suffered at least a 50% loss and that the remaining population underwent a change in breeding phenology, a breakdown in breeding synchrony, and a widespread failure to fledge chicks in the years following the spill. As a result of these effects, it was projected that the population would take 20–70 years to recover.

    Principally because of the paucity of prespill data on the Barren Islands murre population size and reproductive success, it is impossible to quantify any effect of the spill on these populations. Available prespill data (1976–1978) on the East Amatuli murre population size ranges from 19 000 to 61 000 birds. These data are not systematic, replicated counts but rather are estimates indicating a broad range within which the true attendance figure probably resided. Our postspill attendance counts range from 31 041 to 37 128 (1990–1992). Comparisons between matched historical and 1990s photographs showed nearly identical attendance patterns, although there were significantly more murres in the 1990s photographs. Postspill attendance data from multiply censused areas suggest a recovery may have been taking place because of greater than expected annual increases (+25% from 1990 to 1991).

    Prespill data on reproductive activity of the murres nesting in the Barren Islands were collected from a single 5 × 5-m plot located in a dense, flat section of the East Amatuli Light Rock colony. Comparisons with similarly collected postspill data suggest that phenology, egg production, and chick production are extremely variable among years, athough chicks were fledged in all years. Egg and chick production were highest in 1977 and 1991 and lowest in 1992.

    On the basis of these analyses, we conclude that, although murres rafting near the Barren Islands undoubtedly suffered substantial mortality as a result of the Exxon Valdez oil spill, there is no justification for claims of either a dramatic reduction in colony attendance or substantial failure of the remaining birds to settle and reproduce, in the years following the spill. In spite of continued perturbations to the system from both natural and human-induced sources, East Amatuli Island continues to support a large, reproductively active colony of murres.

    Keywords:

    Common Murre, Barren Islands, Exxon Valdez, attendance, reproductive success, environmental change


    Paper ID: STP19882S

    Committee/Subcommittee: E47.13

    DOI: 10.1520/STP19882S


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