Killer Whale Victim Identified by Biologists with New DNA Evidence

Biologists have uncovered the victim of a killing. Observers on a NOAA Fisheries marine mammal survey watched as a pod of killer whales killed a marine animal, leaving only its lungs and heart behind. Now, scientists have learned exactly what the whales killed and then ate with DNA evidence.

"We didn't know what the animal was," said Brittany Hancock-Hanser, one of the researchers, in a news release. "But given the capacity of our lab and how much work we've done on cetaceans, we knew we had a pretty good chance of figuring that out."

In order to find out what species was killed, the researchers turned to the Southwest Fisheries Science Center. It houses one of the largest collections of tissue and DNA samples from marine mammals and sea turtles in the world, all preserved in giant freezers. In fact, it includes about 175,000 tissue samples from roughly 145,000 unique animals and more than 60,000 samples of DNA representing virtually every known species of marine mammal and sea turtle. Each sample also has a unique barcode linked to a database with details about where it came from and how it has been studied.

Needless to say, this database is a powerful genetic tool. This allowed the researchers to compare the genetics of the animal that they discovered with the DNA in the database. First, the researchers extracted DNA with enzymes that permeated the lung tissues that they recovered and opened its cells. Then, they cleaned the DNA through a series of alcohol washes over several days. They then replicated the DNA to provide enough copies to analyze in the laboratory.

So what did they find? After comparing the genetic sequence to the database, they found that the victim had been a pygmy sperm whale. This species of small whale isn't much larger than many dolphins, and is rarely seen. In fact, this is the first documented evidence of killer whales preying on pygmy sperm whales in the Pacific Ocean.

"We weren't able to get there soon enough to see just what was going on," said Hancock-Hanser. "But through genetics we could piece together what happened and learn something new from the result."

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