Underwater Vessel Noise in the Haro Strait

Lindsay H. RobinsonUniversity of Puget SoundIntern with Beam Reach

Marine Science and Sustainability School

Photo: Lindsay Robinson

Orcas’ Acoustic Environment• Orcas may be threatened in U.S.

and are endangered in Canada• ~ 100 whale watching vessels

interact with orcas every summer day in the Haro Strait

• This doesn’t include tankers, cargo ships and other commercial vessels.

• Vessel sound may disrupt the orcas’ ability to echolocate and communicate.

• Orcas responded to Navy ship in May 2002 by grouping together and staying at the surface.

• How loud are these boats?• What is the orientation of sound?• What implications might these

have on policy?

Photo:Guen Jones

•Study siteHaroStrait Friday

Harbor•Vancouver Island

Procedure and Instruments

• Cat’s Cradle was used as typical privately owned boat.

• At 3500 rpm’s, vessel ran transect from me on shore, over fixed hydrophones 0, 1 and 2.

• I used a laser range finder to measure distances.

• Sound was measured from approaching and departing vessel.

Photo: Val Veirs

•Me

H1H2

H0

H3

Analysis Methods• I used computer

sonogram program to find received levels from hydrophone 0.

• Formula for source level:

Source Level=

Received Level + Transmission Loss

Photo: Patrick Duffy

Source Level Results

Min

(dB)

Max (dB)

RL0 120 133

SL0 147 157

•Average Source level is 152 dB re 1µPa @ 1 meter.

Source Level w/ my spreading model

0

2

4

6

8

10

147 149 151 153 155 157

Source Level (dB)

Number of Events

Preliminary Asymmetry• Average SL for

approaching vessel:

154 dB re 1µPa @ 1m • Average SL for

departing vessel:

156 dB re 1µPa @ 1m • More data must be

analyzed to make any conclusions.

Departing Spreading Model dB rec = -15.219 Log R + 156.01

R2 = 0.8006

115

120

125

130

135

140

1 1.5 2 2.5

Log Distance

Recieved Level

Approaching Spreading Model

dB rec= -8.2364 log R + 144.16

R2 = 0.5674

dB rec= -15.421x + 154.32

R2 = 0.9817

120

125

130

135

140

1 1.2 1.4 1.6 1.8 2 2.2

Log Distance

Received Level

In context

• Source Levels of the Washington State Ferry, a whale herding device and an average orca call

• Received Level is an important perspective given different distances.

Photo: Val Veirs

Cat Pipe WSF Orca

SL 152 164 215 160

Dist. 100m 1km 10km 10m

RL 132 134 175 150

Assuming cylindrical spreading

Implications

• This study showed a method for measuring source levels that can be used on other vessels.

• “Be Whale Wise” guidelines may need to be updated.

• Vessels departing from whale watching may be inadvertently directing the most noise orcas.

Photo : Guen Jones

Conclusions

• Small private vessels probably aren’t the most disturbing sound in the area (Unless they are really close!)

• Other boats may prove to be asymmetrical or too loud to be in 100 meter range of orcas.

Photo: Lindsay RobinsonPhoto : Guen Jones

Sonogram frequency spectrum