Human disturbance of harbor seals behavior (fwd)

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Date: Thu Oct 25 2001 - 19:47:56 EDT

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    Subject: Human disturbance of harbor seals behavior

    A new article titled: "Human Disturbances Affect Harbor Seal Haul-Out
    Behavior: Can the Law Protect These Seals From Boaters?" by Barbara
    Lelli and David E. Harris, has been published in Macalester
    Environmental Review. This article is published in electronic form
    only. You can find the article at:


    Over 30,000 harbor seals inhabit the near shore waters of the Gulf of
    Maine. They leave the water (haul-out) primarily onto rock ledges to
    rest, sleep, give birth and nurse their young. Federal legislation, the
    Marine Mammal Protection Act of 1972 (MMPA), protects harbor seals from
    human disturbance, including non-lethal disturbances that disrupt
    normal behavior.

    We observed the harbor seal population that hauls-out at low tide on
    two rock ledges in Gun Point Cove, Casco Bay, in the southern Gulf of
    Maine. Throughout four consecutive Augusts (1997 - 2000) we counted the
    number of harbor seals hauled out at each low tide between 7 AM and 7
    PM. We also determined the level and type of boat traffic passing the
    ledge, the off shore weather conditions (temperature, wave height and %
    possible sunshine - from the nearest weather buoy), as well as the
    current status and enforcement of the MMPA (from statutory law, case
    law and the agency responsible for enforcing this law).

    Using multivariate analysis, we found that the number of seals hauled
    out correlated positively with off shore wave height but negatively
    with % possible sunshine. We also found that the level of boat traffic
    in the cove was, by far, the single strongest predictor of harbor seal
    haul-out number, accounting for 27% of its variability. In 122 days of
    observation, we observed 85 incidents in which the harbor seals were
    flushed off their haul-out ledges. Of these, 93% were caused by boats.
    Because most (526/565=93%) of the boats passing the ledge were motor
    boats, this boat type caused the majority of flushing events. However,
    55% of paddled boats caused flushing events whereas only 11% of motor
    boats did so. We also observed no enforcement of the MMPA in Gun Point
    Cove. Our legal research determined that the MMPA has been used to
    prosecute lethal harassment of seals, but we could find no indication
    that the MMPA has ever been used to deter disturbances of the type we

    We have found that human disturbance by boat traffic has a large impact
    on harbor seal haul-out behavior on near-shore ledges in the Gulf of
    Maine. However, while the MMPA has been used successfully to deter
    human activity that directly and immediately harms seals, penalties
    have not been imposed to prevent harassment by boaters. This suggests
    that education of boaters and clear regulations may be a reasonable
    first step in reducing the impact of boaters on harbor seals in the
    Gulf of Maine.

    Aldemaro Romero, Ph.D.
    Macalester Environmental Review, The Electronic Journal on
    Environmental Studies
    Environmental Studies Program,
    Macalester College,
    1600 Grand Ave.,
    St. Paul, MN 55105-1899, USA
    (651) 696-8157
    (651) 696-6443 (fax)

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