Beaked Whale Strandings in the Mariana Archipelago Associated with Sonar

[Photo of a pair of Cuvier's beaked whales by Jenny Trickey, taken under SEMARNAT permit SGPA/DGVS/000451/18.]

A new study by scientists at NOAA and Scripps Institution of Oceanography at UC San Diego has found that beaked whale strandings in an area of the western Pacific Ocean have been associated with naval sonar. 

Researchers examined eight stranding events of Cuvier’s beaked whales in the Mariana Archipelago since 2007 and found that three of these strandings occurred either during or within six days after naval anti-submarine sonar operations. One to three whales were involved in each event.

They also found that multiple species of beaked whales inhabit the Mariana Archipelago throughout the year, similar to other island-associated populations around the world. The study was published Feb. 19 in the journal Proceedings of the Royal Society B: Biological Sciences.

The Mariana Archipelago consists of the islands of Guam to the south and the Commonwealth of the Northern Mariana Islands, including Saipan and Tinian, to the north. It has been designated as a strategic location by the U.S. Department of Defense, and serves as the principal U.S. military training and basing location in the western Pacific. Biologists have been recording marine mammal strandings in the archipelago for more than 25 years. 

The researchers found that from August 2007 to January 2019 there were eight beaked whale stranding events, of which at least three occurred at the same time as major naval anti-submarine operations. The likelihood that this occurred by chance is less than one percent, suggesting that there is a highly significant relationship between anti-submarine sonar and beaked whale strandings on Guam and Saipan.

“This study is relevant because we identified important beaked whale habitat around the Mariana Islands and document that naval anti-submarine sonar activity is putting these animals at risk,” said lead author Anne Simonis, an acoustic ecologist affiliated with NOAA and alumna of Scripps Oceanography. 

Since 2010, NOAA’s Pacific Islands Fisheries Science Center has been collecting acoustic recordings using High-Frequency Acoustic Recording Packages (HARPs) at two deep-water sites in the Northern Mariana Islands. The long-term acoustic record captures the sounds of whales and dolphins, allowing scientists to document the presence of these species. It also records sounds from human activities such as shipping traffic and military sonar. NOAA and Scripps researchers compared the acoustic data with records of naval activities and the eight stranding events to come to the conclusion that these beaked whale strandings are affiliated with sonar.

“We did not expect to see as direct a relationship between sonar exercises around the Mariana Islands and beaked whale standings over such an extended period of time,” said study coauthor Simone Baumann-Pickering, an acoustic ecologist at Scripps Oceanography. “Together with NOAA and the U.S. Navy, we will have to continue our work on understanding the cause and effect of sonar use and beaked whale strandings and implement better strategies on how to mitigate harmful exposure during naval exercises in the region.”

Beaked whales hold the world record for deepest and longest dives among marine mammals: 2,992 meters (9,816 feet) and 137.5 minutes, respectively. Given their long dives and preference for deep water habitats, people rarely see beaked whales at the surface. As a result, researchers have not yet been able to estimate the population size of Cuvier's beaked whales in the Mariana Archipelago. 

Throughout their range in the Northern Hemisphere, beaked whales are known to be particularly sensitive to mid-frequency active sonar, which is used by navies to detect and locate ultra-quiet submarines. Since it was introduced in the 1960s, there have been 12 documented mass strandings of marine mammals that were associated with sonar activities. These occurred in the Bahamas, Canary Islands, Greece, and Italy. Dozens of strandings have occurred in the vicinity of naval activities in other locations, but there was no direct evidence associating them with mid-frequency active sonar. 

Beaked whales may change their normal diving behavior by surfacing too quickly when they encounter navy sonar. This behavior may cause bubbles in their blood, joints, and vital organs, similar to decompression sickness (“the bends”). This may make whales vulnerable to stranding when exposed to naval sonar activities, but scientists don’t understand the exact relationship between beaked whales and sonar.

Identifying the cause of death in sonar-associated strandings is challenging because skilled technicians need to promptly examine carcasses before they begin to decompose. In remote places such as Guam and Saipan, this is often difficult.

Following a rare stranding of two beaked whales on Saipan in 2011, researchers examined the acoustic records for naval sonar activities. Both recorders detected sonar for more than 10 hours the day before the first beaked whale stranded. Between 2010 and 2014, both recorders detected sonar on 35 days, with the sonar events lasting from 1 to 18 days. Since acoustic monitoring was not continuous throughout that time, there may have been other sonar events that the recordings did not capture.

Researchers also compared the public record of sonar operations on the Marianas Island Range Complex with the eight standing events of beaked whales on Guam and Saipan.  

Although one additional stranding, in January 2019, is associated with a known training event, the U.S. Navy has confirmed that sonar was not used until after the stranding date. NOAA Fisheries worked closely with the U.S. Navy to confirm the publicly available details of other Navy training, testing, and operational sonar use. NOAA and the U.S. Navy continue to work together to ensure that complete and accurate data are available for scientific research.

While they forage, beaked whales use species-specific echolocation clicks that are recognizable in the acoustic record. (Listen to a Cuvier's beaked whale here.) The recent study showed that Mariana Archipelago contains important habitat for at least three species of beaked whales. They are Cuvier’s, Blainville’s, and a third unidentified species that may be the ginkgo-toothed beaked whale. The consistent presence of beaked whales in the area suggests that there may be high chances of sonar-associated beaked whale strandings throughout the year.

This study highlights the value of passive acoustic monitoring for visually cryptic beaked whales as well as naval sonar activity, researchers said. This is particularly valuable in remote regions with few opportunities for visual surveys or established stranding networks beyond Guam and Saipan. 

In addition to Simonis and Baumann-Pickering, co-authors include Robert Brownell Jr. of NOAA’s Southwest Fisheries Science Center, Erin Oleson of NOAA’s Pacific Islands Fisheries Science Center, Bruce Thayre and Jennifer Trickey of Scripps Oceanography, and Roderick Huntington, a Mount Edgecumbe High School student who got involved with this research through Scripps’ SeaTech program. Brent Tibbatts and the Guam Department of Agriculture, Division of Aquatic and Wildlife Resources also provided information on stranding records. 

Funding for deployments and recoveries of HARPs and analysis of mid-frequency active sonar was provided by NOAA PIFSC. Funds for the detection and classification of beaked whale signals within the HARP datasets were provided by U.S. Navy Pacific Fleet through interagency agreements (grant nos PIC-14-002, PIC-15-007, PIC-16-007), and the Cooperative Institute for Marine Ecosystems and Climate (grant no. NA15OAR4320071). This work was also supported by the NOAA John H. Prescott Marine Mammal Rescue Assistance Grant Program.

– Adapted from NOAA’s Pacific Islands Fisheries Science Center

Attached file: Cuvier's beaked whale clicks