Val Veirs

Colorado College

Colorado Springs, CO

Source Levels of Orca (Orcinus Orca) Social Vocalizations Measured with a Shore-Based

Hydrophone Array

S-19 Call -- 169 dB re 1Pa @ 1m

Array of hydrophones is permanently deployed on the west side of San Juan Island, Puget Sound.

Orca Vocalization and Localization -- OVAL

Each spring for the past 5 years a group of undergraduate physics majors from Colorado College have worked at the

site – deploying, repairing, operating …

OVAL Hydrophone ArrayFour ITC hydrophones with student-build preamps are deployed on fixed, weighted stands in depths from 12 to 45 meters.

The seafloor descends at a nearly uniform 30o to depths of 200 m at 400m from the shore.

The frequency bandwidth of these detectors is 100Hz – 10kHz and signals are digitized at 22050 Hz.

Southern Resident Orcas

The three pods of Southern Residents, ~85 animals, pass by the OVAL array many times over the four month summer season – May to September.

Sometimes they vocalize and sometimes they are close to the hydrophone array.

Localization via Cross Power Spectra and Matched Field

Processing

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Minimization of composite error between source location modeled differences and observed differences finds best estimate of source location.

Downhill Simplex:

Cross Power Spectra for 3 Pairs of Hydrophones

Calibration of Hydrophone

Array

Chirps are sent to the hydrophones from J-9 underwater projector from known depths and GPS locations.

Accuracy of Source Locations  Mean Error (m) Standard

Deviation (m)East-West difference 0.01 9.3

North-South difference 0.7 14

Vertical difference 2.9 21

Range difference 0.7 15.7

Spreading ModelChirps sent from J-9 at source level of 140 dB re 1 Pa @ 1 m show average decrease in received level with distance is close to cylindrical spreading.

Source Level CalibrationHistogram of calculated source level for 50 chirps from underwater projector operating at 140 dB re 1 Pa @ 1 m.

Summer 2004 Orca Passbys

The OrcaSound hydrophone array ran continuously from May through September.

The system triggered on orca social vocalizations on 24 separate passbys on 19 different days.

A total of 1.84 Gb of acoustic data was automatically recorded during these passbys. All of these signals passed amplitude vs time profile constraints designed to accept transient signals that include orca vocalizations.

445 Orca Calls Near the ArraySelection Criteria: Events

Passing:

The localization must be of adequate quality (Q > 6) and the distance from any hydrophone and the localized position must be less than 400m (this distance is ~ twice the array aperture).

 602

The frequency structure of the call must be “orca-like”. There must be a relatively small number of prominent peaks in the power spectra that persist continuously for periods of time ~ a half a second or more during the call.

 456

A trained observer checked to hear and see if the recording is an orca vocalization.

445

Source Level Distribution 445 orca vocalizations within 400 m of hydrophones

Source SPL (dB) vs Logarithm of Body Mass (kg)SPL = 21.458 Log(mass) + 86.135

R2 = 0.6114

90

100

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190

1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00

Log(m ass in kg)

SPL

(dB

)

Harbor porpoise

Spinner Dolphin

Dall's porpoise

BottlenosedolphinRiver dolphin

Sperm w hale

Short-f inned pilot w hale

Killer w haleRichardson Table 7.2

Southern ResidentOrcas -- Tw ostandard deviation SPL range reported here

Source levels from Richardson, “Marine Mammals and Noise” and recent dolphin report (Janick 2000) and manatee report (Phillips 2004)

Reported Source Levels of non-Echolocation Vocalizations of

OdontocetesRegression line:

acoustic pressure (Pa) at one meter from vocalizing animal = 20 mass (metric tons)

Mean Passby Source Level vs Call Rate(24 Passbys)

dB = 1.0832 Call Rate + 143.01R2 = 0.2832

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154

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00

Localized Calls per Minute During Passby

dB S

ourc

e Le

vel

Error bars are standard error of the mean.

Midnight -- 7calls

3 am -- 17 calls

Peculiar Bifurcation and Quiet Nights

Passby Average Source Level vs. BackgroundSource dB = 0.3601xBackground dB + 106.6

R2 = 0.2779

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154

95 100 105 110 115 120

Background dB

Aver

age

Sour

ce L

evel

dB

Midnight

3 am

Background Noise and Average Source Levels

Acknowledgement and Thanks

March 2000: Tami Beitzel, Jonah Huckabay, Rois Langner, Vik Sarkar, Davis Thomson March 2001: Kat Baker, Hannes Hubmayr, Bethany Marsh, Amos Ngola March 2002: Anderson English, Paul Guidice, Winn Jewett, Peter Richardson, Michael Silk, Hillary Swanson, Erika Danforth, Matt Ayres, Molly Yoder-Williams March 2003: Luke Galli, Brian Hurlbutt, Winn Jewett, Bill Morton, Sara Schuster, Zach Van Hilsen March 2004: Liz Martin, Craig Peterson, Luke Roberts, Nick Santorsola, Max Stevens, Yulan Qing

Colorado College Students:

The Colorado College Physics Department and Faculty Research CommitteeThe Whale Museum of Friday Harbor and Dr. Rich OsborneLeslie Veirs and Scott Veirs