You’ve likely seen Jack and Daisy, harbour porpoises (Phocoena phocoena), and thought, “Hey, they’re cute,” but what you may not know is that they’re not just cute faces; they’re main players in an important research project.
In the last year, research scientist Dr. Jason Mulsow from the National Marine Mammal Foundation has been working with Vancouver Aquarium researchers to conduct hearing tests on the beluga whales, Pacific white-sided dolphins, harbour porpoises and Chester, the false killer whale. Dr. Mulsow was recently joined by Dr. Jim Finneran, a research scientist with the U.S. Navy Marine Mammal Program, to further investigate how hearing works in harbour porpoises. More specifically, they wanted to find out how sound arrives simultaneously in both ears.
Harbour porpoises produce high-frequency sounds to echolocate. Echolocation works similarly to sonar. Whales, dolphins and porpoises (cetaceans) direct sounds through a fatty organ (melon) in their heads. Then, they listen for the return echo as those sounds to bounce off of objects. The echo travels back through their fat-filled lower jaws and into their inner ears, allowing them to create a mental picture of their surroundings.
The Aquarium trainers, who had worked very closely with the porpoises to get them to this point, moved them from their habitat to an area behind the scenes, one after another. Daisy was up first, and the researchers played sounds held at different points along her jaw line. The conductors placed on her head picked up her brain waves which could be read on the computer. The idea was to find the best location or “sweet spot” along the jaw so scientists in the future can quickly and consistently assess a cetacean’s hearing ability.
Ultimately, this research will help us understand why cetaceans strand and, in a rescue and rehabilitation scenario, whether their ability to echolocate has been compromised. Dr. Finneran says an animal that can’t echolocate would be seriously compromised in the wild. It would have little success of surviving if it couldn’t hunt and avoid predators using echolocation. Aquarium Marine Mammal Rescue staff had to be sure Levi could echolocate before his successful release in 2013.
The scientists have a special interest in Jack and Daisy because they are the only harbour porpoises in a North American facility. Dr. Finneran says they have done similar research with over 100 bottlenose dolphins, but because their skulls and head shapes are different, there is a need to collect baseline data for harbour porpoises as well. They also plan to continue testing Chester’s hearing as he grows.
Written by Karen Horak, writer-editor, content and digital experience at the Vancouver Aquarium.