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:
http://www.macalester.edu/environmentalstudies/MacEnvReview/articles.htm
ABSTRACT
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
observed.
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.
Editor-in-Chief
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)
romero@macalester.edu
http://www.macalester.edu/environmentalstudies
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