Prelimnary Project Findings
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Research Summary
Our preliminary findings indicate that
the haddock aggregations were present soon after our deployments
began on Jefferies Ledge
and the onset of vocalizations seems to coincide with local fishermans
knowledge of haddock spawning. Figure 3 is
an example of series of haddock calls recorded on Jefferies Ledge
at 1:45 pm on 8 May, 2003:
Figure 3. Waveform of haddock calls on Jefferies Ledge (23 sec.).
Date: 5/8/03 Time: 1:45pm ID: Haddock calls, Jeffries Ledge
This is
a clean, easily identified signal accompanied by relatively low
levels ambient sea-state noise. Earlier in that same deployment
we were surprised to see the 15-min. recording shown in Figure
4. This reveals the acoustic environment is being dominated
by sound that arrives at exactly 18-seconf intervals. After some
investigation we learned that Marathon Oil Corporation had begun
seismic tests in a location known as the Gully, southwest of
Sable Island east of Nova Scotia. In spite of these sounds, we
are able to identify haddock calls, which can be seen as lower-amplitude
signals in between the air gun blasts. Such pollution from oil
and gas activity can persist for hours and days depending on
the schedule of the survey ships and the acoustic conditions
of the waters between the source and our listening station.
Figure
4. A 15-minute recording from Jefferies Ledge showing seismic
testing off Sable Island.
Date: 5/8/03 Time: prior to 1:45pm ID: seismic testing, Jeffries Ledge
Figure
5 shown another series of haddock calls recorded on May
9 that occur along with the 18-second seismic blasts. So far
we are unable to conclude whether this level of persistent
anthropogenic noise has an effect on fish vocalization rates.
Two other examples of haddock calls are presented in Figures 6 and 7.
The latter is likely the latter stages of spawning activity
during which courtship vocalizations grow in intensity and
repetition rate.
Figure
5. A characteristic pre-spawning haddock call mingled with seismic
blast (41 sec.)
Date: 5/9/03 Time: unknown ID:haddock calls, Jeffries Ledge
Figure
6. May 9, Jefferies Ledge, 1:20 pm, haddock calls
Date: 5/9/03 Time: 1:20pm ID: haddock calls, Jeffries Ledge
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Figure
7. May 9, Jefferies Ledge, 1:47 pm, spawning haddock calls (90
seconds)
Date: 5/9/03 Time: 1:47pm ID: spawning haddock calls, Jeffries Ledge
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Whale
calls are also common on Jefferies Ledge and are easily detectable. Figure
8 is a three-call sequence, probably representing more than
one whale.
Figure
8. Three whale calls recorded on Jefferies Ledge at 6:00 am on
11 May (28 sec.)
Date: 5/11/03 Time: 6:00am ID: Whale calls, Jeffries Ledge
Based
on cursory viewing of waveforms and manual comparisons of the
sounds with know laboratory and field recordings, we have found
that most of the haddock acoustic activity occurs late afternoon
and evening. A shorter waveform display of a single whale call
is shown in Figure 9, showing the characteristic
45 Hz. of a fin whale.
Figure
9. Waveform of a fin whale recorded on Jefferies Ledge at 2:00
pm on 8 May (1.4 sec.)
Date: 5/8/03 Time:2:00pm ID: Whale calls, Jeffries Ledge
There
are many sounds that require speculation as to their source. Figure
10 is an example recorded at 4:00 am on 10 June 12 miles
to the east of West Cod ledge of Portland. This record is one
of many in a sequence that go on for over 4 hours.
Figure 10.
A 15-min. record of repeating unknown sounds east of West Cod
Ledge.
Date:
6/10/03 Time 4:00am ID: unknown sounds, 12miles E of West
Cod ledge of Portland.
One of
the signals is expanded in Figure 11 and
some who have listened to it suspect these might come from whales
bubble feeding with the open-mouthed breach at the end.
Figure
11. An expansion of a signal from Figure 8 (39 sec.)
Date: 5/11/03 Time: 6:00am ID: Whale calls, Jeffries Ledge
Another
example of an unknown sound was recorded on 22 June 3 miles to
the northwest of the above location at 9pm. These differ in some
respects to those shown in Figure 10 and
they endure for nearly three hours. One possible explanation
is the hauling of lobster gear . However, the late evening time
suggests that the activity might be clandestine. That same night
we recorded two unusual sounds that sound like rifle shots and
they are shown in Figure 13.
Figure
12. Another 15-min. record of repeating sounds off Portland,
possibly night lobstering.
Date: 6/22/03 Time:9:00pm ID:unknown sound, NW of West Cod Ledge, Portland,
Maine
Figure
13. Two distinct signals that sound like rifle shots 22
June, 7:25 pm (0.6 sec.
Date: 6/22/03
Time: 7:25pm ID: possible gun shots
In summary, our recording to date have demonstrated what we had hoped, that
our listening stations can detect spawning vocalizations.
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