Analysis and Ranking of the Acoustic Disturbance Potential of ...

Report No. 6945
BBN Systems and Technologies Corporation
Guard icebreaking activities to one large Polar Class vessel in Alaskan waters
and USCG icebreakers do not routinely support oil industry operation.
The F-4C fighter aircraft is included in the table as a representative
loud jet aircraft. Most commercial aircraft are 10 to 20 dB quieter, and
small civil aviation aircraft 20 to 30 dB quieter. On a sound pressure basis,
the source level of the F-4C can be seen to be equal to that of the icebreaker.
(The underwater sound reference level of 1 vPa has been used for
both sources. )
Noise levels from large military and commercial aircraft are highest near
airports. In other areas these aircraft usually fly at high altitude which
considerably reduces their noise at ground level. Small aircraft and helicopters
often fly at low level along shorelines and estuaries to aid
navigation. This procedure produces sporadic high noise levels on the ground
near the flight paths.
The large tanker example shown in the table is a steam turbine driven
vessel which represents the upper range of large merchant vessels. Some
supertankers may have up to 5 dB higher source 1evels.depending on their
propulsion plant and propeller design.
The major shipping industry sources in Alaska are the larger cargo,
container, and tanker vessels that operate from the southern Alaska ports of
Anchorage, Valdez, Seward and Kodiak to either the "lower 4811 or to Japan.
The route that is most important from the standpoint of potential marine
mammal noise impact is the route to Japan which goes along the Alaska
Peninsula and through Unimak Pass. This is also the route used by fishing
vessels and cargo shipments, generally with tugs and barges, to the settlements
along the Bering Sea coast and the Arctic.
The vessels operating for the tourist industry are also a significant
part of the Alaskan marine environment. The cruise ships and ferries
operating in Southeast Alaska, with acoustic source levels that range from
170 to 180 dB, maintain a schedule with typically more than 20 vessels per
week along passages and channels frequented by humpback whales and other
marine mammals.
The vessels used by the fishing industry are less powerful than the
icebreakers and large tankers represented in Table 6.1. Their acoustic source
levels are lower, typically ranging from about 170 dB for trawlers at full
speed to 160 dB for smaller high speed sports-fishing vessels. When operating
individually, these vessels do not have as much noise impact potential as the
larger cargo ves-sels and tankers. While the source levels of individual boats
are relatively modest, the combined effect of several vessels operating at
high speed in the same area can produce a zone of high sound level which is
comparable to that produced by a much larger vessel. This type of effect is
likely to occur during openings of fishing for restricted species where
concentrations of vessels are present. Vessel concentrations may persist
through the season in areas where species do not disperse. The major fishing
vessel locations are Homer in Kachemak Bay, Kodiak Island, Seward, Sand Point,
Dutch Harbor, and the settlements aJong the east end of Bristol Bay.