Orcas give boats silent treatment
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INTRO: Killer whales communicate in a language scientists don't fully understand. But one thing scientists have figured out is that the whales stop talking whenever too many boats are around. Orcas and noise, next on Arctic Science Journeys Radio.
STORY: Johnstone Strait, near Vancouver, British Columbia, is a haven for killer whales, also called orcas. These sounds of orcas were recorded by a network of undersea hydrophones planted in the strait. Throughout the summer, more than 300 of the giant black-and-white marine mammals gather here to feast on salmon.
The strait is also a haven for people and their boats. University of Alaska Fairbanks graduate researcher Carrie Talus recently completed her master's degree on how orcas responded to noise made by passing fishing vessels, ships and tour boats.
TALUS: "Well, this area has quite a big whale-watching industry. There are often many boats following a pod of killer whales, and people will relay over the radio when they see this group, and everyone rushes over there. Most of the time these whales have an entourage of boats following them."
Talus studied killer whale recordings made by Orca Lab, a nonprofit research center in Vancouver. Since the hydrophones also recorded boat traffic in the area, Talus could hear how boats changed whale behavior.
TALUS: "The biggest thing I found was that they decrease their call rates by about 50 percent when there's boat noise. So they call a lot less. I can't say that they're being disturbed, because I don't really know. But I can say they're calling less, and we can speculate that maybe this is reducing their communication efficiency."
Vocalizations are important to marine mammals like killer whales to keep track of one another, to identify friend or foe, as well as to navigate and hunt prey.
TALUS: "The calls I was looking out for are called pulse calls, which are their communication calls. What I did was make spectrograms of these calls on the computer. And spectrograms are basically pictures of the calls that show the frequency structure of the call through time, and then the intensity at each frequency of the call. For the spectral characteristics, I looked at the duration of the calls and I looked at the average frequency of the first harmonic. These calls have many harmonics in them. And I also looked at the number of harmonics in the calls."
Talus can't say if the boat noise had a detrimental effect on the orcas she studied, but studies done elsewhere have found a correlation.
TALUS: "There have been some studies that have shown increased boat traffic causes whales to actually leave an area altogether. This has been seen with humpback whales off Hawaii. They left an area when human activities increased a lot in this bay. And they just didn't come back for years, until the boat traffic decreased again and they came back again. And then it was seen in grey whales in a calving lagoon in Baja, California. They just stopped going there."
OUTRO: This is Arctic Science Journeys Radio, a production of the Alaska Sea Grant Program and the University of Alaska Fairbanks. I'm Doug Schneider.
Our thanks to the following individual for help in the preparation of this script:
If you'd like more information about orcas, check out this web site:
Arctic Science Journeys is a radio service highlighting science, culture, and the environment of the circumpolar north. Produced by the Alaska Sea Grant College Program and the University of Alaska Fairbanks.
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