Nala the sea lion presses a paddle with her nose, then looks up expectantly. A fish appears — her reward for hearing a faint tone no human ear could detect. At Taronga Zoo Sydney, Nala and three other marine mammals are helping scientists understand how seals and sea lions experience sound in air — and how human noise might be disrupting their lives.
This research matters because Australian sea lions are endangered, with only about 12,000 left in the wild. They rely on sharp hearing to find food, avoid danger, and stay in touch with their pups. But coastlines are getting noisier. Ships, boats, planes, and construction projects send rumbles and hums through the air and water. Before we can protect these animals, we need to know what they can actually hear.
That’s where Nala and her fellow test subjects come in. Scientists from Curtin University and Taronga Conservation Society Australia trained two Australian sea lions and two long-nosed fur seals to take part in voluntary hearing tests. Using fish as rewards, the animals learned to press a paddle whenever they heard a tone. This method revealed the first detailed hearing profiles — called audiograms — for both species in air.
The results show both species are most sensitive to sounds around 3.2 kilohertz, a frequency similar to a high-pitched whistle. That means common human-made noises — like boat engines, aircraft, and construction equipment — fall well within their hearing range, especially when the animals are hauled out on shore. For the endangered Australian sea lion, this could mean constant noise disrupts rest, communication, or awareness of predators.
"Before we can understand whether a noise is affecting an animal, we need to know whether it can hear that noise in the first place," said Professor Christine Erbe of Curtin University, lead researcher on the study. The findings are already being used to guide environmental impact assessments, helping planners make smarter decisions near seal and sea lion habitats.
Dr. Benjamin Pitcher, a behavioral biologist at Taronga, emphasized that the animals were never forced to participate. They chose to join the tests, staying engaged through positive reinforcement. This approach not only protects animal welfare but also yields more accurate results.
Now that scientists know what these animals can hear in air, the next step is to study how underwater noise affects them — and when it starts to change their behavior. With this knowledge, conservationists hope to create quieter, safer coastlines for some of Australia’s most vulnerable marine mammals.