Marine Mammals





1. Introduction

Humpback whales (Megaptera novaeangliae) annually migrate from their summer
feeding grounds off southeast Alaska to winter in waters off the Hawaiian
Islands, Baja California Sur, Mexico and northern Japan (Baker and
Darling). The number of humpback whales in the Hawaiian waters generally
peaks from mid-February through mid-March ( Baker & Herman, 1984). Calving
and breeding is an important function of humpback whales while wintering at
lower latitudes ( Herman and Herman et al., 1980). The presence of these
whales has spawned a popular and rapidly growing whale-watching industry.
Whale watches are undertaken with a wide assortment of vessels. Because of
the ever-growing number of boats involved, concerns are often expressed by
those in the whale-watching industry, environmental groups and governmental
agencies about the effects of vessel disturbance on the whales ( Green,
1998).

Humpback whales have been observed to react to approaching boats in a
number of different ways ranging from approach to avoidance. On rare
occasions, humpback whales have been observed charging towards approaching
boats and screaming underwater (Payne, 1978). Bauer (1986) and Bauer and
Herman (1986) found that respiration rates, diving, swimming speed, social
exchange and aerial behaviors correlated with vessel numbers, proximity,
speed and direction changes. They reported that humpback whales generally
attempted to avoid vessels and sometimes directed threats towards them.
Increased frequencies of surfacing without blows and dives initiated
without raised flukes were some behaviors indicative of avoidance. Green
and Green (1990) reported that humpback whales often reduced the proportion
of time at the surface, took longer dives, altered direction as the boats
approached (horizontal avoidance) and continued to spend more time
underwater and decreased swim speed (vertical avoidance) after boats
departed. These effects persisted over 20 min after the boats departed.
Green (1990) also observed that humpback whales moved from a favored area
on days when parasail boats operated. Bauer and Herman (1986) concluded
that reactions to vessels probably are stressful to humpback whales but the
significance of the stress is unknown.

Research performed by Baker and Herman (1989), Baker, Herman, Bays and
Stifel (1982), Baker, Herman, Bays and Bauer (1983), and Bauer (1986) in
Alaskan waters suggests that humpback whales usually use two main type of
avoidance methods. The first involves a vertical avoidance in which the
dive duration increases, with a corresponding decrease in the blow interval
and in swim speed. The second method involves a horizontal avoidance in
which there is a decrease in the dive duration, longer blow intervals and
an increase in swim speed. Baker, Herman, Bays and Stifel (1982) and Baker,
Herman, Bays and Bauer (1983) also found that approaching boats often
triggered some aerial behaviors such as breaching, flipper and tail
slapping.

There appears to be little doubt that boat traffic may affect the behavior
of humpback whales. Examples of such disturbance by vessels on humpback
whales in Hawaii can be found in Tinney (1988) and in the humpback whale
recovery team report ( HWRT, 1991). Consequently, the National Marine
Fisheries Service (NMFS), the Federal agency primarily responsible for
enforcing the Marine Mammal Protection Act, has imposed a regulation
prohibiting boats from approaching within 91 m (100 yards) of any humpback
whale in Hawaii ( NMFS, 1987).

One issue that has not received much attention is the specific effect of
boat noise on the whales. All boats from the smallest motor boat to the
largest super-tanker produce underwater noise. However, there is limited
information on noise produced by small boats typically used in coastal
waters (Richardson, Greene, Malme & Thomson, 1995). Considerably more
attention has been focused on large ocean-going vessels. McCauley, Cato and
Jeffery (1966) have measured the noise generated by whale-watching vessels
in Hervey Bay, Australia. Many of these boats in Hervey Bay operated as
ferrys and modify their routine slightly upon encountering a pod of whales.
Present regulations in Hervey Bay for approaching whales state that boats
must slow within 300 m of whales, which is very different than the 91 m
standoff range in Hawaii with no speed limitations. It is also difficult to
apply noise measurements from one location to another because underwater
acoustic propagation can vary considerably depending on the depth and types
of bottom.




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