"Long before it's in the papers"
January 27, 2015


Weird ocean sound finally explained: a whale

April 23, 2014
Courtesy of NOAA FIsheries Service
and World Science staff

A strange un­der­wa­ter sound whose source was a mys­tery for dec­ades comes from minke whales, bi­ol­o­gists have con­clud­ed. The find­ing, they say, has been ac­comp­an­ied by sur­pris­ing new facts about the whale’s move­ments, and should yield more in­forma­t­ion.

The odd rhyth­mic sound was first re­ported by sub­ma­rine sail­ors in the 1960s. They called it the “bio-duck” sound be­cause they thought it sounded like a duck. Recorded since at var­i­ous loca­t­ions in the South­ern ocean, it’s now be­ing at­trib­ut­ed to the Ant­arc­tic minke whale, Bal­aen­op­tera bon­ae­ren­sis. The find­ings were pub­lished April 23 in the journal Bi­ol­o­gy Let­ters.

Bio-duck sound sam­ple. Cre­dit: De­nise Risch, NEFSC/NOAA

Last year, re­search­ers put acous­tic “tags” on two Ant­arc­tic minke whales in Wil­hel­mi­na Bay off the west­ern Ant­arc­tic Pen­in­su­la. Sci­en­tists led by De­nise Risch of Na­t­ional Oceanic and At­mos­pher­ic Ad­min­is­tra­t­ion’s North­east Fish­er­ies Sci­ence Cen­ter then an­a­lyzed the da­ta and iden­ti­fied the sound.

A se­ries of deep pulses, it’s heard mainly dur­ing the south­ern win­ter around Ant­arc­tica and off Aus­trali­a’s west coast. No one knew those whales were there. The find­ing in­di­cates some minke whales stay in ice-covered Ant­arc­tic wa­ters year-round while oth­ers make sea­son­al migra­t­ions fur­ther north, the sci­en­tists said.

Antarctic minke whale. (Cre­dit: NOAA/John W. Dur­ban)

“These re­sults have im­por­tant im­plica­t­ions for our un­der­stand­ing of this spe­cies,” said Risch. “We don’t know very much about this spe­cies,” she added, but the tags pro­vide “an op­por­tun­ity to change that, es­pe­cially in re­mote ar­eas.” 

Sci­en­tists on a hard in­flat­a­ble boat used poles to tag the an­i­mals. The tags recorded sounds, wa­ter tem­per­a­ture and pres­sure. No oth­er ma­rine mam­mal spe­cies were ob­served in the ar­ea when calls were recorded, the sci­en­tists said.

The sci­en­tists did­n’t in­i­tially rec­og­nize the mys­te­ri­ous sounds as the “bio-duck,” in­stead at­trib­ut­ing them pos­si­bly to sub­ma­rines, some ocean­o­graphic phe­nom­e­non, or even fish. They made the con­nec­tion to the “bio-duck” sound af­ter check­ing pub­lished lit­er­a­ture. 

Minke whales, which have been vic­tims of Jap­an­ese whal­ing expe­di­tions, are the small­est of the “great whales” or ror­quals, a group that in­cludes the blue whale, Bry­de’s whale, and hump­back, fin, and sei whales. Ror­quals are rath­er stream­lined, have point­ed heads and, ex­cept for hump­back whales, small point­ed fins.

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A strange underwater sound whose source was a mystery for decades comes from minke whales, biologists have concluded. The finding, they say, has revealed surprising facts about the whale’s movements and habits, and should lead to other new information. The odd rhythmic sound, recorded for decades in the Southern Ocean, was first reported by submarine personnel in the 1960s. They called it the “bio-duck” sound because they thought it sounded like a duck. Recorded since at various locations in the Southern ocean, it’s now being attributed to the Antarctic minke whale, Balaenoptera bonaerensis. Last year, researchers put acoustic “tags” on two Antarctic minke whales in Wilhelmina Bay off the western Antarctic Peninsula. Scientists led by Denise Risch of National Oceanic and Atmospheric Administration’s Northeast Fisheries Science Center then analyzed the data, identified the sound and published the findings in the April 23, 2014 in Biology Letters. The sound, a series of deep pulses, is heard mainly during the southern winter around Antarctica and off Australia’s west coast. No one knew those whales were there. The finding indicates some minke whales stay in ice-covered Antarctic waters year-round while others make seasonal migrations further north, the scientists said. “These results have important implications for our understanding of this species,” said Risch. “We don’t know very much about this species,” but the tags provide “an opportunity to change that, especially in remote areas.” Scientists on a hard inflatable boat used poles to tag the animals. The tags also recorded water temperature and pressure. No other marine mammal species were observed in the area when calls were recorded, the scientists said. The scientists didn’t initially recognize the mysterious sounds as the “bio-duck,” instead attributing them possible to submarines, huge fish or some oceanographic phenomenon. They made the connection to the “bio-duck” sound after checking published literature. Minke whales are the smallest of the “great whales” or rorquals, a group that includes the blue whale, Bryde’s whale, and humpback, fin, and sei whales. Rorquals are rather streamlined, have pointed heads and, except for humpback whales, small pointed fins.