The increase in whales washing up on Mariana shores is likely due to the Navy's sonar use, according to a new scientific study published this month.

Half of the incidents involving stranded beaked whales in the region were within days of Navy activity in the water. The probability that these whales stranded by chance amidst the training is extremely low, at 0.1%, the study stated.

The first incident was a beaked whale washing ashore alive in Piti in 2007. Since then, there has been a strong association between beaked whale strandings with the presence of multinational naval antisubmarine warfare training operations in the region, the study stated.

No beaked whale strandings were reported in the Mariana Archipelago between 1962 and 2006. But from 2007 to January 2019, along with an uptick in military activity, eight beaked whale strandings were reported on Guam and Saipan — 50% of these events were within days of reported naval operations.

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In January 2019, an 11-foot, 1,000-pound beaked whale was found on the reef flats off the waters of Agat, following the Navy's anti-submarine warfare training, Exercise Sea Dragon.

The Pacific Daily News last year reported that the Navy proposed continued sonar use throughout the region's waters in its latest supplemental environmental impact statement, despite an increase in beaked whales washing up on Guam's shores and research indicating sonar is correlated with such incidents.

The environmental impact statement is expected to be finalized this year, which will formalize more sonar use in Guam's waters, along with other training and testing activities.

Many residents weren't happy about this, expressing concern regarding sonar use in the region's waters during a public meeting last year on the environmental impact statement.

A common diver's ailment, decompression sickness, is a possible reason whales strand after sonar exposure, according to research published January 2019. The effects of long-term exposure to sonar are unknown due to the lack of data on beaked whales in general, but any effects of decompression sickness have clear impact on the welfare of whales.

Canary Islands sonar ban

Antonio Fernandez, co-author of the 2019 study and veterinary histology and pathology professor at the University of Las Palmas of Gran Canaria, stated that prompt political action in Spain resulted in a remarkable conservation success for marine mammals in the face of sonar use.

The Canary Islands, where much of his research was conducted, saw 18 beaked whales strandings between 2002 and 2004. In 2004, Spain banned sonar use around the Canary Islands. There have been no strandings since the ban.

"The Canary Islands were a hot-spot for mass strandings of beaked whales before 2004," Fernandez said. "But there have been no new mass strandings since the moratorium, proving the effectiveness of this mitigation, and the link between these strandings and naval exercises with antisubmarine mid-frequency sonar."

High risks

This latest research hones in specifically on the Marianas, and the likelihood that the whales washing up on Guam's and Saipan's shores are due to naval sonar.

Beaked whales may be particularly susceptible to sonar. The infrequent sonar activity, combined with the "quiet ambient noise levels" of the waters in the region, may increase the severity of the behavioral response of beaked whales, according to the study.

"The high association of beaked whale stranding events with antisubmarine warfare and sonar activity, with the relative lack of beaked whale strandings before 2007, suggest that there may be high risks of sonar-associated beaked whale strandings in the Mariana Archipelago," the study stated.

More monitoring, full disclosure

Consistent stranding networks are needed to monitor and respond to individual and mass strandings, the study stated. In addition, full disclosure on the part of the military regarding the timing and position of mid-frequency active sonar events would support more robust assessments of the potential risk for sonar-associated strandings.

"We strongly recommend more visual monitoring efforts, at sea and along coastlines, for stranded cetaceans before, during and after naval exercises," the study added.

The Pacific Daily News asked the Joint Region Marianas for comment on the morning of Feb. 20. It hadn't provided comment as of 5 p.m. Feb. 21.

Reporter Anumita Kaur covers military, business and tourism on Guam. Follow her on Twitter @anumitakaur. Reach her at akaur@guampdn.com.