Acoustic Monitoring Program
New: Listen to underwater
sounds!
Click here for location of underwater
cable and precautions
Underwater Acoustic Monitoring in
Glacier Bay National Park
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What is the underwater noise monitoring program? In May
2000, Glacier Bay National Park (GBNP) staff and U.S. Navy acousticians
installed an underwater listening device - called a hydrophone –
in the entrance of Glacier Bay. The hydrophone transmits underwater
sounds through a cable to a computer workstation at Park headquarters
in Bartlett Cove. Navy acousticians have begun to analyze and summarize
the data and provided
reports to the Park.
What can you hear with the hydrophone? The hydrophone detects
natural and human-made sounds. Wind,
rain, snow and earthquakes all produce distinct underwater sounds.
Whale vocalizations are
also audible when they are in the area. We can also hear sounds
made by other animals,
and possibly some fish. We will also be able to hear vessels
passing by. Skilled acousticians will determine whether the sounds
we recorded are wind, rain, an outboard engine, or a cruise ship.
This picture shows an example of the computer display produced
when a motor vessel passes by the hydrophone.
What was the impetus for this project? In 1996, GBNP completed
its Vessel Management Plan, designed to accommodate increased visitation
to the park while protecting sensitive park resources. The Plan
regulates the number of vessels allowed to enter the bay, and implements
vessel course and speed restrictions in areas where whales are present
(referred to as ‘whale waters’). Although GBNP has a variety
of resource concerns related to vessel traffic, park staff are particularly
concerned about the potential disturbance of endangered humpback
whales by vessel noise.
Why monitor underwater sounds? Endangered humpback whales
feed during summers in Glacier Bay. Research shows that whales may
move away from preferred feeding areas when disturbed by vessel
sounds. Repeated disturbances could be detrimental to Alaskan humpbacks,
who must feed enough during the summer to sustain themselves through
their 3,000 mile roundtrip migration to and from Hawaii. Vessel
noise can also interfere with whale communications, increase the
opportunity for collision between vessels and whales, or cause short
or long-term hearing loss.
Park staff are interested in learning what, if anything, can be
done to minimize sound disturbance of marine mammals in the park.
The data gathered during this study will help park managers fine-tune
vessel management regulations.
The specific objectives of the research are to:
- Describe ‘natural underwater sounds" such as wind,
rain, and animal vocalizations
- Describe vessel-generated sounds (frequency, loudness, duration,
and how far the sound travels) in lower Glacier Bay
- Determine the frequencies and loudness of vessel-generated sound
that whales and other marine life are exposed to
- Determine how vessel numbers, speed and other operating parameters
affect underwater sound
How loud is too loud? Does the Park have an upper threshold
of acceptable noise? Not yet. Once we have collected data on
the proportion of underwater noise that comes from vessels, the
sound levels marine mammals are exposed to, and how much variability
in sound levels there is on a daily basis, the Park will work with
Navy acousticians to develop "noise goals". "Noise
goals" will then guide the Park’s vessel management practices.
Is the park interested in all vessel noise, or just cruise
ship noise? We are able to "hear" all vessel types
using the hydrophone. While larger vessels like cruise ships are
certainly loud at greater distances than smaller vessels, other
types of vessels can produce equivalent underwater noise levels
at close range. In 1999, 5 cruise
ships volunteered to individually visit the Navy’s underwater
listening station in Ketchikan to obtain a vessel "sound signature".
The resulting data allowed GBNP to evaluate the effects of engine
type and operational conditions (including speed, engine RPM and
propeller pitch) on their underwater sound output. In fall 2000
and 2002, we obtained similar 'sound signatures’ of a variety
of Park Service
vessels in Bartlett Cove by asking them to navigate near the
hydrophone at a specified course and speed. The results are available
in reports found
on this web site. If you are planning to be in Bartlett Cove and
are interested in obtaining a sound signature for your vessel, please
contact Chris Gabriele@nps.gov.
Will acoustic monitoring results lead to more restrictions on
vessels in Glacier Bay? Gathering underwater sound data will
allow park managers to evaluate its vessel management policies.
For example, ambient
noise data have revealed that lower Glacier Bay is quieter on
average when there is a 10 knot speed limit in effect, compared
to when the speed limit is 20 knots. However, many other factors
will also be considered before any changes are made to the existing
regulations including: navigational safety, the risk of whale/vessel
collisions, visitor experience and effects on other Park resources.
In some cases, regulations could become less restrictive.
How will the Park correlate vessel noise data with marine mammal
behavior? After collecting at least one year of ambient noise
data, wehope to conduct a behavioral study of whales and other marine
mammals to determine what effects vessel sounds have on them. Numerous
other studies have shown that vessel noise can cause whales to change
their diving and respiratory intervals and be diverted from feeding
or resting. Our proposed study would go beyond what is presently
known about disturbance by comparing actual underwater sound levels
and food availability to whale behavior.
Where can I go to hear the sounds being received by the hydrophone?
Data collected by the hydrophone is available on all computers
on the Park’s computer network. We hope to place a "listening
station" and interpretive display in the Park Visitors Center.
In the meantime, please feel free to call Chris Gabriele at 907-697-2664
to arrange a time to visit her office and listen to the present
underwater sound conditions in Glacier Bay.
Where is the cable laid and how can
I avoid snagging it with my boat anchor or fishing line? The
hydrophone and cable are not marked with a buoy or in any
other fashion and the cable will likely bury itself in the sand
or mud and won’t be visible either. However, they are both
very vulnerable to damage from anchors, long-lines or clam diggers.
Cutting the cable or pulling on it could damage its ability to conduct
sound. Moving the hydrophone anchor could bury the hydrophone or
damage it.
- The hydrophone and anchor are in approximately 100 ft of water,
at the location indicated on the map.
- The cable is laid in very shallow water along the Lester Island
shoreline, but should not be exposed except at tides lower than
–4 feet below mean lower low water. Even at the highest tides,
the cable should be in less than 40 feet of water even at the
highest tides.
NOTE: The hydrophone and cable location and a
complete description are published in the U.S. Coast Guard’s
"Notice to Mariners" as well as on the park's website.
 How
can people avoid damaging the hydrophone cable?
- Avoid bottom-fishing, anchoring, setting a crab pot, or clam
digging in the vicinity.
- Do not anchor, bottom-fish or set a crab pot in less than 20
feet of water along the south shore of Lester Island.
- If you are fishing or anchoring in the area and snag something
strong on the bottom, which you suspect may be the hydrophone
cable, consider cutting your line.
- Before clam digging near Lagoon Island or Lester Island get
a detailed description of the cable location from Chris Gabriele.
What should I do if I inadvertently damage or pull up the cable?
Report the event and its location (a GPS position would be ideal)
to Park staff immediately. The cable can be repaired if it is broken,
but we must know where the break is. If you snag something really
tough, or pull up a ½" diameter black cable, or know that you
have cut the cable, call the Visitor Information Station, or Chris
Gabriele at 907-697-2664.
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