Killer whales raise their voices to be heard over boat noise, and the effort may be wearing the whales out as they try to find food amid dwindling numbers of salmon, new research says.
The killer whales of Puget Sound make more calls and clicks while foraging than while traveling, suggesting that such mealtime conservations are key to coordinating hunts, the work reveals
Several types of vessels, from small whale-watching boats to large cruise ships, also traverse the coastal waters off Washington State and neighboring British Columbia, Canada.
"[The killer whales'] call exchange is incredibly important … and vessel noises have the potential to mask these calls," said research leader Marla Holt of Seattle's Northwest Fisheries Science Center, which is run by the National Oceanic and Atmospheric Administration (NOAA).
Holt and colleagues' previous research had shown that some killer whales make louder calls to be heard over vessel rumblings—just as people raise their voices to talk over the din of a cocktail party.
Now the researchers think the cacophony could be causing the region's killer whales to use up more energy during hunts, even as their preferred prey, chinook salmon, are on the decline.
Killer Whales' Mysterious Drop
In Puget Sound a small group of killer whales known as the Southern Residents has been found to be particularly well-suited to eating salmon—even down to the whales' tooth size.
These animals don't eat seals or other mammals, as do the transient killer whales that migrate through the sound.
In the mid- to late 1990s the Southern Resident population mysteriously shrank by nearly 20 percent, from 97 to 88 animals. Today there are 85 individuals.
In 2005 the federal government listed the population as endangered under the U.S. Endangered Species Act.
No one knows for sure, but the cause was likely a combination of fewer salmon, exposure to toxic contaminants, and vessel noise, according to Lynne Barre of NOAA's National Marine Fisheries Service Northwest Regional Office.
Barre's agency released a recovery plan for the dwindling mammals in early 2008, with the goal of boosting the population by about 2 percent a year over 28 years
Part of that plan involves monitoring the effects of vessel traffic on killer whales.
Social Calls
Killer whales are social animals that live in tight-knit pods of about 20 to 40 individuals, and they rely on calls that are "group badges" unique to each pod, she said.
Since 2007 Holt and colleagues have been recording vessel noise with underwater hydrophones off the San Juan Islands. The team records about 3,280 feet (1,000 meters) away from a group of whales then notes the animals' behaviors—foraging, traveling, resting, or socializing—every ten minutes.
Holt, who will present the team's preliminary findings in October at the Biennial Conference on the Biology of Marine Mammal in Quebec, said that their research indicates killer whale communication is particularly important during hunting.
What's more, previous studies in birds had suggested that the animals consume more oxygen to raise their voices above ambient noise, making their metabolic rates spike and burning up stored energy, Holt said.
It's possible the same phenomenon could be occurring with killer whales, although it's too early to know for sure, she added.
Keep Your Distance
Holt's work adds to existing data that have already prompted NOAA to propose a new killer whale protection law that would make all boats keep at least 600 feet (200 yards) away from the animals around Washington State.
The existing law allows boats to approach as close as 300 feet (100 yards), and some research has shown this influences the whales' behavior.
"A lot of people would argue, Why focus on these vessel regulations?" Holt said. "But it's one thing we can do immediately."
But Ken Balcomb, director of the Center for Whale Research in Friday Harbor, called the proposed law a "feel-good thing."
Balcomb, who has also studied whales in the San Juan Islands, said that "my observations over 35 years [are] that [whales] don't really get disturbed by anything, much less vessels."
No Salmon, No Whales
The main concern, Balcomb said, is the decline in chinook salmon, particularly those of the Fraser River in Canada. That salmon run has declined precipitously in recent years.
Dams on rivers in the Pacific Northwest, as well as housing developments built in estuaries where young salmon take refuge, have devastated the once abundant fish.
Researchers have already seen that bad salmon years—when fewer fish make their way downriver into Puget Sound—usually become bad whale years.
"If you deny them the food, [there's] basically no point in worrying about other factors," Balcomb said.
NOAA's Barre noted that the federal whale-recovery plan also supports efforts to revive the salmon runs that reach Puget Sound.
For instance, conservationists in the region have been working to remove dams to boost salmon populations, a strategy that has been successful with Atlantic salmon on the U.S. East Coast.
But if the fish don't come back, the Southern Residents may eventually abandon Puget Sound—a sad prospect to Balcomb.
"We like to see them here," he said. "It's the icon of our healthy ecosystem."
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