Disturbances from Vessels
Due to
the large number of vessels that regularly visit or transit the sanctuary,
the effects of boat traffic on marine mammals is a concern. Much of
the concern regarding disturbance of marine mammals has focused on isolated
incidents, where a vessel has caused a change in behavior of one or
more whales. Although these incidences capture public attention, it
is likely that the more serious consequence of vessel disturbances is
potentially the cumulative effects of many vessels to cause an abandonment
or decrease in use of an important habitat (Tyack, 1990). Assessing
the cumulative effects of vessel activity on marine mammals in the Sanctuary
will require long-term monitoring and evaluation of vessel use for comparison
with detailed observations regarding marine mammal occurrence, distribution,
and behaviors collected over a similar time frame.
Central
to efforts to minimize the effects of vessels on marine mammals is the
issue of "harassment," a term defined under the Marine Mammal
Protection Act as " any intentional or negligent act that substantially
disrupts the normal behavior of an animal." Thus while marine mammals
are protected by federal law, the task of determining whether harassment
has occurred requires both knowledge of what normal behavior is and
the ability to determine when an animal has been disturbed. Determining
what constitutes "normal" behavior in marine mammals is complicated
by the lack of detailed behavioral data for many species, the inherent
difficulty in studying these oceanic species without disrupting or biasing
their behavior, and the tendency of some species to become habituated
to certain types of stimuli over time. Certain studies which have attempted
to describe whale reactions to vessels are reviewed below.
Disturbance
from vessels may be considered from a number of different aspects. Examples
of stimuli from vessels which may be disturbing to some species of cetaceans
include: a vessel which is too close or in danger of striking an animal,
active pursuit or circling of animals, interfering with feeding or other
activities, and vessel noise. To evaluate the effects of vessel activity
on cetaceans some measure of avoidance behavior is typically used, such
as swimming away from the source of disturbance or a change in the behavior
which immediately preceded the disturbance (Brown, et al. 1991, Weinrich
et al. 1991). However, because cetaceans conduct many activities in
bouts with shifts in behavior and breathing rates occurring naturally,
it is often difficult to distinguish avoidance behaviors from "normal"
reactions.
Watkins
(1986) reviewed data from 25 years of observation to determine the effect
of vessel exposure on four species of cetaceans, humpback whale (Megaptera
novaeangliae), fin whale (Balaenoptera physalus), northern right whale
(Eubalaena glacialis) and minke whales (Balaenoptera acutorostrata).
Reaction to three types of stimuli associated with vessels were evaluated
including underwater sound, light reflectivity, and tactile sensation.
Reactions were categorized as either positive, uninterested, or negative.
Positive reactions included those of apparent curiosity or interest
and often involved a close approach or interaction with human activity.
Uninterested reactions were those in which the stimuli were apparently
ignored and negative reactions included sudden changes from activity
to inactivity, persistent movement away from the stimuli, and immediate
startle response such as turning sharply away or diving.
In this
study, sound proved to be the primary cause of reaction with most whales
responding to sounds with frequencies from approximately 15 Hz to 28
kHz. They appeared to ignore sounds of low amplitude or those with the
most energy at frequencies above or below their hearing. Negative reactions
were associated with a wide range of underwater sounds including those
that were unexpected, too loud (above a 12 dB increase over previous
ambient sounds), suddenly louder, or were associated with a perceived
threat (e.g. rapid vessel approach). Approximately 50 percent of all
whales avoided continuous noise at levels of 120 dB.
Similarly,
unexpected notice of brightly reflective objects, such as a boat hull
or aluminum instrument housings often caused a startled and avoidance
reaction by all species studied. However, habituation sometimes occurred
quickly, within a few hours, with animals approaching close enough to
touch objects that were initially avoided. Tactile stimulation appeared
to be a less important response than either hearing or vision, but some
whale reactions appeared to depend on their expectation of the "feel"
of particular objects. Unfamiliar objects were sometimes approached
quite closely (within a few centimeters), but were initially rarely
touched. Increasing familiarity and experience with an object may eventually
lead to touching, and familiar objects like seaweed, logs, and fish
boxes are often touched and lifted repeatedly by individual whales.
Watkins
also reported that the type of reaction differed for each species and
that these reactions changed over time. Changes in reactions which occurred
over the time period studied may be summarized as follows: minke whale
responses to vessels changed from one of frequent positive interest
in vessels to one of general disinterest; fin whale responses changed
from mostly negative to uninterested; right whales showed the same varied
response pattern, which was often negative; and humpback whales indicated
a dramatic change from mixed responses which were often negative to
responses which were often strongly positive. In some instances, if
whales appeared preoccupied with certain activities, such as feeding
or social activity, they might ignore sounds that previously generated
a negative response. As suggested by this study, a whale's observable
response to vessels and vessel stimuli may differ depending upon prior
experience and thus familiarity with the stimuli present. The effects
of habituation to certain stimuli should be considered in future research
of this type.
The effects
of whale watching on whales has come under increased scrutiny in recent
years as both its popularity and the size of the industry have grown.
According to Tilt (1985), whale watching activity in the Stellwagen
Bank area represents the most concentrated whale watch center in North
America. The level of activity in the area has remained high and consequently
efforts to determine and minimize any effects to endangered cetaceans
is an important conservation priority. The northeast region of the National
Marine Fisheries Service (NMFS) typically receives 6 -12 reports of
"harassment" due to vessels a year (Tilt, 1985).
In 1988,
the National Marine Fisheries Service convened a workshop on whale watching
which involved researchers, government officials, and industry representatives.
The purpose of the workshop was to review whale watching activities
and available information on the effects of whale watching on the whales
in order to provide NMFS with direction on how to protect whales from
potentially harmful activities associated with this activity. Workshop
participants addressed both short and long-term research needs, educational
programs and options for regulating the industry. The relevant priority
recommendations for research included areas with small populations subjected
to whale watching, such as right whales in the northeast and those identified
as critical to significant numbers of whales for key activities such
as feeding. Both of these priorities apply to the Sanctuary and the
adjoining right whale critical habitat in Cape Cod Bay. Specific research
recommendations addressed, among others, the need to determine short-term
behavioral changes as indicators of disturbance, techniques for monitoring
physiological indicators of stress, and quantifying the effects of acoustic
disturbance. The workshop also recommended the development of regulations
establishing minimum approach distances based upon regional considerations
(including type of species, location, habitat use, and behavior) which
appear to influence whale reactions to vessels. There is also general
support that restrictions which establish minimum approach distances
ought to pertain to activities other than whalewatching, including recreational
boats, thrill craft, and swimmers (Anon., 1988).
Currently
the New England whale watching fleet operates under a voluntary set
of guidelines which recommend the following safe operating procedures
for maneuvering vessels in the vicinity of whales: no head-on approaches,
no more than one vessel within 300 feet of a whale at any time (close
approach zone), and a no-approach zone of 100 feet from a whale. In
addition, the guidelines recommend a 600 foot (distance from whale)
stand-by zone for no more than three vessels and a 1500 foot cautionary
or whale awareness zone, where no sudden changes in speed or direction
should be made by a vessel. The guidelines have been available since
1984 and are used by the NMFS to educate vessel captains and the general
public about the potential harm caused to whales by vessel activity.
In general, the guidelines are respected by the commercial whale watching
operators, but compliance may vary depending upon whale abundance, time
constraints, vessel operator, and/or weather conditions (David Mattila,
pers. com.). Disregard and/or ignorance of the guidelines by recreational
boaters remains a serious problem, especially during peak summer periods.
Recently
NMFS proposed whale watching regulations to establish uniform minimum
approach distances of 100 yards for all whales and 50 yards for dolphins
and porpoises in U. S. waters (Fed. Reg., Vol. 57, No. 148, 1992). Ultimately,
this proposal was withdrawn in response to the widespread criticism
received from commentors, many of whom felt it ignored the recommendations
of the 1988 workshop discussed above.
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