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.
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."
SOURCES AND RELATED WEB SITES