Update: SONAR Recorded off of San Juan Island

Posted April 9, 2009 at 3:31 pm by

Jen­ny Atkin­son is the direc­tor of the Whale Muse­um, and she files this update to Jean­ne’s report from yesterday:

Begin­ning at 7 p.m. on April 7, hydrophones oper­at­ed by The Whale Muse­um and Beam Reach Marine Sci­ence and Sus­tain­abil­i­ty School start­ed pick­ing up unusu­al sounds.  Hydrophones off the coast­line of Lime Kiln State Park and anoth­er node about 4 km north record­ed SONAR pings and what sound­ed like gar­bled human speech.  These sounds became alter­nate­ly loud­er and soft­er in one or the oth­er of the two hydrophone receiv­ing loca­tions.  Record­ings of SONAR and oth­er sounds con­tin­ued until Wednes­day, April 8, 3 a.m. PST.  The sounds from these hydrophones stream live via the inter­net on the pub­lic-acces­si­ble site www.orcasound.net.  Sam­ples of the record­ed sounds are archived there.

Exam­i­na­tion of the record­ed sounds shows that the sound lev­els at the south­ern loca­tion, Lime Kiln Light­house, were usu­al­ly high­er than at the more north­ern loca­tion off the west-side of San Juan Island.

It is like­ly that the sound source was gen­er­al­ly south of San Juan Island.  Dr. Val Veirs, pres­i­dent of the The Whale Museum’s Board and pro­fes­sor of Physics (emer­i­tus) at Col­orado Col­lege, stat­ed that “The received lev­els of the sig­nals at Lime Kiln Light­house were about the most intense sounds that the hydrophones there have record­ed in the past sev­er­al years of con­tin­u­ous operation.”

The high­est received lev­els came from SONAR pings. The high­est received lev­els were approx­i­mate­ly 140 dB re 1 microPas­cal.  This is approx­i­mate­ly the same as the most intense SONAR sig­nals record­ed in May 2003 when the US Navy Guid­ed Mis­sile “Shoup” tran­sit­ed the waters of Haro Strait (here’s the report). The base fre­quen­cy of the SONAR pings was about 3 kHz which sug­gests that the SONAR is the Navy’s mid-fre­quen­cy sonar which was impli­cat­ed in the death of mul­ti­ple beaked whales in the Bahamas Octo­ber 2003.

Dr. Veirs said that “We have been told that the US Navy report­ed that a sub­ma­rine, the USS San Fran­cis­co, was oper­at­ing in the Strait of Juan de Fuca at the time that we made our obser­va­tions and that the ‘gar­bled voic­es’ we heard were used for com­mu­ni­ca­tion between the sub­ma­rine and a sur­face ten­der.  We esti­mate that the dis­tance  between our hydrophone at Lime Kiln Light­house and the sub­ma­rine was in the neigh­bor­hood of 10 nau­ti­cal miles and for our hydrophones to pick up the strong sig­nals that they did, the sub­ma­rine was emit­ting sound with source lev­el in the range 175 dB to 225 dB re 1 microPa@1m.”

These sounds were heard for many miles in a vari­ety of under­wa­ter loca­tions from the east at Whid­by Island, to the north of San Juan Island and out toward the ocean in the Strait of Juan de Fuca.  The Whale Muse­um has not received reports of strand­ed or injured marine ani­mals.  If you see an injured or strand­ed marine mam­mal, please con­tact the San Juan Coun­ty Marine Mam­mal Strand­ing Net­work (800–562-8832).

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