Do sharks hear underwater sounds? Most people would say sharks find things by smell, a drop of blood in the water and the shark is on its way. Scientists at Florida Atlantic University tested hearing in wild blacktip sharks and found they can hear low sounds from far away and tell where those sounds are coming from. Marine biologist Andrew Lewin, host of Ocean Decoded and co-host of the Beyond Jaws podcast, breaks down how the study worked and why it changes how you should think about sharks.
Every winter, blacktip sharks gather in shallow, clear water off Palm Beach County in Southeast Florida. Caroline Sullivan, working with Professor Stephen Kajiura and Edmund Gerstein, used that aggregation as a natural lab. The team anchored a boat, played low sounds from 100 to 800 hertz through an underwater speaker, measured the sound with hydrophones and filmed every shark from a drone hovering 40 to 50 metres overhead. Sharks reacted from as far as 74 metres away, or 243 feet, and turned sharply away from the speaker. A 10,000 hertz control tone got no reactions at all. More than 70% of the reactions happened in the acoustic far field, the first time free-swimming sharks have been shown responding to sound that far out. The study is published in the journal Integrative Organismal Biology.
Andrew then connects the findings to the noise we put in the ocean. The blacktips reacted most strongly between 100 and 400 hertz, and commercial ships put most of their underwater noise below 500 hertz. The study didn't test noise pollution, and it comes with three limits: one species, shallow clear water, and loud sounds played to startle the sharks. You'll leave with one question to ask every time you read a shark story, what are they hearing?, plus ways to help: count noise as an ocean threat, slow down near reefs and coastal shark habitat if you boat, and support underwater noise rules for shipping and coastal construction. Join Andrew live on Ocean Decoded Live, Monday to Thursday at 5 PM Eastern, and go deeper with Beyond Jaws, co-hosted with Dr. David Ebert, and How to Protect the Ocean.
Chapters:
0:00 - Sharks and the Movie Version of Smell
1:39 - The Setup: Speaker, Hydrophones and a Drone
3:01 - The Far Field
4:51 - The Corrected Picture
5:32 - Ask "What Are They Hearing?"
Takeaways:
Sharks use smell, sight, the lateral line, electroreception and hearing, and hearing is the sense most shark stories leave out.
Hearing is hard to study in tanks because sound bounces off the walls, so the FAU team worked with wild blacktips in the ocean.
The study used an underwater speaker, hydrophones and a drone filming 40 to 50 metres overhead off Palm Beach County, Florida.
Blacktips reacted to low sounds from as far as 74 metres (243 feet) away.
The sharks turned sharply away from the speaker, showing they could locate the sound as well as detect it.
The two lowest sound ranges got reactions more than 80% of the time, the 400 to 800 hertz range about 71%, and the high control tone none.
Lower sounds could be quieter and still get a reaction.
More than 70% of reactions happened in the far field, a first for free-swimming sharks.
Sharks have no swim bladder and rely on the inner ear, including the macula neglecta, to sense particle motion.
The blacktips responded most strongly between 100 and 400 hertz, the same range where ships put most of their underwater noise.
The study tested one species, in shallow clear water, with loud startle sounds.
When you read a shark story, ask: what are they hearing?
#OceanConservation #MarineBiology #SaveOurOceans #ProtectTheOcean #OceanAwareness #BluePlanet #ConservationMatters #ScienceForChange #SustainableOceans
--------------------------------------------------------------------------------------------------------------------------------------------
Follow a career in conservation: https://www.conservation-careers.com/online-training/ Use the code SUFB to get 33% off courses and the careers program.
Do you want to join my Ocean Community?
Sign Up for Updates on the process: www.speakupforblue.com/oceanapp
Sign up for our Newsletter: http://www.speakupforblue.com/newsletter
Facebook Group: https://bit.ly/3NmYvsI
Connect with Speak Up For Blue:
Website: https://bit.ly/3fOF3Wf
Instagram: https://bit.ly/3rIaJSG
TikTok: https://www.tiktok.com/@speakupforblue
Twitter: https://bit.ly/3rHZxpc
YouTube: www.speakupforblue.com/youtube
