Scientists examining levels of ocean noise in the Bering Sea—an important migratory seascape for whales, walruses, seals, and other acoustically sensitive animals—have confirmed that the presence of sea ice plays a central role in the soundscape of these Arctic waters.
A growing concern is that the disappearance of sea ice due to a changing climate could mean a marine realm increasingly filled with shipping and other human-related ocean noise, according to scientists from Southall Environmental Associates, WCS (Wildlife Conservation Society), and other groups in a new study.
One of the key findings of the paper, published in the journal Marine Pollution Bulletin, is that increasing periods of open, ice-free water are correlated with an increase of non-biological ambient noises, both from surface waves driven by wind and an increase in vessel traffic.
“The study examines one of the world’s most important migratory corridors for marine mammals that is currently undergoing significant changes due to a warming climate,” said lead author Brandon Southall of Southall Environmental Associates, Inc. “The timing and intensity of seasonal presence of sea ice are strongly linked to ambient noise in this important region, a connection that has major implications for protected marine mammal populations that depend on these habitats.”
Arctic species such as bowhead whales (Balaena mysticetus), beluga whales (Delphinapterus leucas), walrus (Odobenus rosmarus), bearded seals (Erignathus barbatus), and ribbon seals (Histriophoca fasciata) are seasonally present and travel through the waters around St. Lawrence Island and the Bering Strait at different points of the year.
The research team deployed 14 archival acoustic recorders at nine sites around the coast of St. Lawrence and in the Bering Strait region of the northern Bering Sea. Between 2014 and 2017, the recorders captured more than 3,000 hours of ambient noise data, including over winter periods under ice. The samples were statistically analyzed to determine trends within the context of season, time of day, and sea ice conditions and concentrations.
The recorders captured ambient noise from both biological and anthropogenic sources. Vocalizations from marine mammal species were recorded according to seasonal presence, with bowhead whales and their vocalizations being most prevalent in December, and bearded seals mostly in May. The presence and sound levels of ships were also recorded and cross-referenced with known AIS (Automatic Identification System) positions.
The ambient noise levels varied across sites, with low frequency noise at similar frequencies to many marine mammal vocalizations being most prevalent in open sea conditions. Also, noise levels from the recorders near the village of Gambell on the northwestern side of St. Lawrence Island, located near the US-Russia Maritime Boundary, were greater than levels offshore from the village of Savoonga, situated farther to the east. But overall, it was the presence or absence of sea ice that drove the occurrence of low and high frequency sounds and their sources.
“Our continued passive acoustic monitoring in the northern Bering Sea provides a much-needed baseline of data on ocean noise that will help identify threats to the region’s seascapes, marine life, and local subsistence activities,” said Dr. Martin Robards, Regional Director for WCS’s Beringia Program.
“The changing conditions and potential levels of noise in this essential Arctic passageway are of great concern for marine mammals. Research on both biological and physical noise sources as part of a larger conservation strategy are clearly important in the years to come,” said Dr. Howard Rosenbaum, study co-author and Director of WCS’s Ocean Giants Program. “Our collective efforts with Alaska Native communities and with regulatory agencies responsible for shipping-related impacts to marine mammals in these areas can factor in noise and marine mammal seasonal patterns for minimizing the impacts to these iconic Arctic species and their important habitats.”
The authors of the study titled “Seasonal trends in underwater ambient noise near St. Lawrence Island and the Bering Strait” are: Brandon L. Southall; Hugh Southall; Ricardo Antunes; Ross Nichols; Andrew Rouse; Kathleen M. Stafford; Martin Robards; and Howard C. Rosenbaum.
Funding for this study was provided by the North Pacific Research Board (Project #1511) and the Flora Family Foundation.