February 1, 2006 — NOAA researchers and their partners have developed passive listening devices designed to record the calls of the Earth's great whales. These moored autonomous hydrophones record sounds in the water, but do not actively emit sounds themselves. The new technology can be applied world-wide to investigate the populations and ranges of the great whales. Locating calling whales enables researchers to identify apparent seasonal shifts in distribution. Correlating these data with current field observations and an extensive historical database of species distributions may help answer critical population and stock management questions. The new technology can be used in all the worlds oceans, but the pioneering program began in the North Pacific. To date, more than 20 listening devices have been deployed in the waters off Alaska. (Click on image for larger view of grey whales off Alaska. Please credit "NOAA.")

A multi-year program initiated in 1999 by the NOAA Pacific Marine Environmental Laboratory in Newport, Ore., and the NOAA National Marine Mammal Laboratory in Seattle, Wash., has advanced the use of passive listening devices designed to record whale sounds by deploying arrays of listening devices in the waters off Alaska. Sue Moore of the NOAA Alaska Fisheries Science Center, Kathleen Stafford of the University of Washington, David Mellinger of Oregon State University and John Hildebrand from the Scripps Institution of Oceanography have led the multi-year effort. (Click on image for larger view of map showing location of passive listening devices deployed in the Alaska study. Click here for high resolution version. Please credit "NOAA.")

"This is a prime example of agencies and institutions drawing together to put together technology and a pilot program that can benefit large whale populations all around the globe,” said Doug DeMaster, director of the NOAA Alaska Fisheries Science Center. “I’m proud of NOAA Fisheries’ strong part in this effort.”

“The program has yielded unprecedented information on the seasonal occurrence and calling behavior of endangered blue, fin, humpback, sperm, right and bowhead whales, as well as non-endangered gray whales,” said Sue Moore, senior researcher with the NOAA Alaska Fisheries Science Center. “And the system delivered this accurate information with little human effort and with no disturbance to the whales.” (Click on image for larger view of image showing right whale sounds recorded by the passive listening devices used in the Alaska study. Click here for high resolution version. Please credit "NOAA." Click here to both see and hear other whale sounds in Alaska.)

“Offshore from Alaska, the devices are particularly useful because standard visual surveys are hampered by darkness and bad weather,” she added.

With the end of the Cold War, the U.S. government allowed marine mammal researchers to listen in to the Navy’s Sound Surveillance System, which had been used to help track submarines, explained Moore. Biologists found the system was also an extremely useful tool to detect blue and fin whale calls over long distances. This provided the impetus for marine mammal biologists and audio technicians to develop autonomous recorders that could be deployed anywhere in the oceans to monitor areas for whale calls, as in this study.

Whale researchers use two types of recorders off Alaska: hydrophones developed by the NOAA Pacific Marine Environmental Laboratory, and acoustic recording packages developed by Scripps Institution of Oceanography.

• The autonomous recorders fabricated by NOAA’s PMEL record acoustic energy from underwater whale calls. The hydrophones are designed to be moored in the oceanic sound channel (or SOFAR channel, for SOund Fixing And Ranging). The titanium case containing the data recorder can withstand pressure to at least 1,000 meters below sea level. These instruments are capable of recording frequencies from 1 - 20,000 Hz, and depending on the sampling rate, can record data for over a year before servicing is required. The hydrophones are designed to be deployed as an array of independent instruments whose geometry can be determined by the needs of the experimenter in order to localize acoustic sources of interest. Currently, more than a dozen of these hydrophones have been deployed in the eastern equatorial Pacific, northern North Atlantic, central North Atlantic, Marianas, and the Gulf of Alaska. (Click on image for a larger view of the illustration showing the autonomous recorder fabricated by NOAA's Pacific Marine Environmental Laboratory for the Alaska study. Please credit "NOAA.")
• Scripps’ Acoustic Recording Packages (also called ARPs) are bottom mounted and provide continuous recording at 500 or 1,000 samples per second for months at a time. The main components consist of a hydrophone (which is suspended 10 meters above a mooring), batteries, ballast weights and a series of electronics handling acoustic release and datalogging. (Click on image for a larger view of the illustration showing the Institution of Oceanography's acoustic recording package used in the Alaska study. Please credit "NOAA.")

Both of the above mentioned listening devices need to be recovered in order to access the recorded data. Scientists must then differentiate the noises made by the whales from noises caused by ships, waves, other species and even the Earth.

Scientists focused much of their early efforts in listening for the critically endangered North Pacific right whale, particularly in the southeastern Bering Sea, where they deployed a total of eight autonomous recording devices. The devices have already shown that right whale calls are concentrated in September and October, but occur from May through November in the southeastern Bering Sea.

The program has increased scientists’ abilities to better differentiate between the similar calls of right whales and humpback whales.

The listening devices have also helped describe the long-distance migration patterns of blue whales in both hemispheres of the Earth, something that could not have been done a decade ago. Before 1999, little was known about the seasonal presence of blue whales in the northern latitudes, or about their population structure. Scientists working with acoustic recordings gathered since 1999 have confirmed that blue whales routinely occur the Gulf of Alaska and that two populations of blue whales may visit there in summer and early autumn. (Click on image for larger view of bowhead whales off Alaska. Click here for high resolution version. Please credit "NOAA.")

In addition, acoustic researchers were surprised to find that both sperm and fin whales stay in the Gulf of Alaska through the winter — previously, most researchers believed that the whales migrated to mid-latitude in winter. Sperm whale clicks occurred roughly half as often in winter as in summer, suggesting that a sizable fraction of the population is present year-around. Most fin whale calls were detected from August through February.

Five recorders, including three new instruments, are scheduled for deployment in the southeastern Bering Sea in April 2006, coincident with mooring sites maintained by the NOAA Pacific Marine Environmental Laboratory. Meanwhile, researchers continue to analyze audio data gathered since 1999 and are refining their interpretation of the data by integration of remotely sensed parameters, such as sea surface temperature and height.

Relevant Web Sites
Monitoring marine mammals using acoustics

Whale Vocalizations and Calls

Whale Biology

Research Projects and Milestones and Related Publications

NOAA Whale Page

Whales in Alaskan Waters

NOAA STUDIES SOUNDS IN THE SEA

North Pacific Research Board

Media Contact:
Connie Barclay, NOAA Fisheries, (301) 713-2370 x 144