Finding the Needle in the Haystack: Using Sonobuoys to Locate a Critically Endangered Species (cont.)
Figure 2. Spectrogram of the upsweep (top) and gunshot (bottom) calls produced by the North Pacific right whale.
Figure 3. Deploying a sonobuoy from the rail of the NOAA ship Oscar Dyson.
Figure 4. A sonobuoy being dropped from the belly port of the Aerocommander during the 2009 right whale aerial survey. Photo by Jeff Foster.
Right whales produce two distinct and easily identifiable vocalizations, the upsweep and the gunshot call (Fig. 2). The upsweep call, with a frequency range of 80-250 Hz, can sometimes be confused with a humpback call. However, humpbacks tend to produce many other varying calls in conjunction with the upsweep, whereas, the upsweep of a right whale typically stands alone. Thus, right whales can often be distinguished from humpbacks by looking at the call in the context of other vocalizations around it. The gunshot call, as the name implies, is a distinctive short, impulsive, broadband sound. By localizing on these two call types, acoustic technicians can direct the boat to within sighting distance of the calling whale.
After a successful 2008 field season using sonobuoys (Fig. 3), passive acoustic monitoring was incorporated into the right whale aerial survey as well. Sonobuoys were deployed from the belly port of the aircraft (Fig. 4), and all receiving equipment was secured to a board that hung on the back of a seat. Because the sonobuoys rely on line-of-sight from the float to the antenna for signal transmission, the aircraft was able to obtain far greater reception ranges than the vessel, which was limited to 10-15 nmi. Right whales were detected by aerial observers on over 55% of the sonobuoys deployed from the aircraft, increasing the overall number of sightings.
Due to their efficiency in detecting calling whales in limited visibility and high sea states, both the aerial and vessel surveys were able to locate right whales more quickly, allowing for more time with the animals and a more productive survey. The right whale project no longer conducts large-scale surveys and, as a result of budget cuts, is limited to only a handful of days piggybacking on transits of other project cruises. Finding right whales quickly is now critical, and using sonobuoys provides the best chance of maximizing the time available with the animals.
Since 2007, over 1,000 sonobuoys have been deployed throughout the Bering, Chukchi, and Beaufort Seas, and they have detected at least nine different cetacean species. The inclusion of sonobuoys not only increases the coverage area of a survey and the number of sightings but also allows us to continue to monitor critically endangered populations even in limited visibility and high sea states.
NMML would like to thank Jeff Leonhard (Naval Surface Warfare Center, Crane Division), Theresa Yost (Naval Operational Logistics Support Center), Todd Mequet (Applied Logistics Services, Inc.), and Captain Robin Fitch (Director of Marine Resources and At-Sea Policy, Office of the Assistant Secretary of the Navy, Installations and Environment) for their continued support in providing us with sonobuoys.
