Fish-Eating Killer Whales in the Pacific Northwest Just Love Chinook Salmon
Whitlow W. L. Au
Hawaii Inst. of Marine Biology,
Univ. of Hawaii,
P.O. Box 1106,
Kailua, HI 96734
John K. Horne
Univ. of Washington,
Seattle, WA 98105
Christopher D. Jones
Univ. of Washington,
Seattle, WA 98105
Popular version of paper 2pAB2
"Backscatter measurements of three species of salmon using simulated killer whale echolocation signals"
Presented at 1:50 p.m. on Tuesday, November 11, 2008.
156th Meeting of the Acoustical Society of America
Some killer whales eat other mammals and some eat only fish. The fish eating killer whales that frequent the waters of British Columbia and Washington State are called “resident” since they tend to spend all of summer and other months in these waters, while the mammal eating species are called “transients” because they tend to swim in and out of these waters. The resident killer whales just love Chinook salmon.
Research by Dr. John Ford of the Pacfic Biological Station, Fisheries and Oceans Canada has clearly shown the strong preference for Chinook salmon. Dr. Ford has been studying foraging resident killer whales over a ten year period by collecting scales of salmon prey after whales catch and share their prey with fellow clan members. They found that Chinook salmon are by far the preferred prey even at time when Chinook are only 10 to 15 percent of the total salmon population. Dr. Brad Hanson of the Northwest Fisheries Science Center in Seattle has also been seen the same pattern in the waters of Washington State.
Killer whales use their biosonar when hunting for prey, often detecting the prey at distances greater than about 50 yards. They emit trains of short pulses that are 0.0001 seconds long. We theorized that the echoes from these biosonar pulses are different when reflecting off different salmon species. In order to test our theory, we measured the reflections from Chinook, Coho, and sockeye salmon using the simulated biosonar signals of killer whales. Our results show that indeed the properties of the echoes from the different species do differ and that these differences can be used by killer whales to determine whether a potential prey is a Chinook salmon or some other species of salmon. These differences are caused by the different shape and volume of the swimbladders. Each species of salmon have swimbladders that are shaped differently and are specific to their species. The killer whales have that all figured out.
When these whale biosonar pulses are slowed down by 45 times, the difference between Chinook and coho salmon is clearly audible -- even to humans. Whales can apparently hear the difference at full-speed.