New publication: Underwater sound production of free-ranging Hawaiian monk seals

Authors: Kirby Parnell, Caroline Smith, Adriana Diaz, Kyleigh Fertitta, Pearl Thompson, Philip T. Patton, Isabelle Charrier, Stacie Robinson, Aude Pacini, Lars Bejder

We are pleased to share a new publication in Royal Society Open Science, which describes the underwater vocalizations made by free-ranging Hawaiian monk seals. This research encompasses Ph.D. Candidate Kirby Parnell’s second chapter of her dissertation which she will be defending on 9^th December (stay tuned for the defense announcement)! The manuscript is entitled: Underwater sound production of free-ranging Hawaiian monk seals. 

Two adult Hawaiian monk seals interacting under water. Credit: Krista Jaspers

Understanding the sound made by an animal that spends a large amount of its life underwater always presents a challenge, even more so when the animal in question is an endangered species and you don’t get many opportunities to record the sound it produces!  

This new study has shed some light on the mystery of Hawaiian monk seal (Neomonachus schauinslandi) vocalizations – and it turns out they produce many more call types and vocalize more often than anyone expected. 

This study was conducted using SoundTraps – an acoustic recording device which can be left on the seabed to record for long periods of time. They were deployed at five key monk seal habitats, ranging from Moloka‘i to the remote Northwestern Hawaiian Islands. 

Sound traps were deployed at five key locations throughout the Hawaiian Archipelago, ranging from Kalaupapa on Molokaʻi  in the Main Hawaiian Islands, to Manawai in the Northwestern Hawaiian Islands.

The recording devices provided more than 4,500 hours of data, from which the analysis team was able to identify more than 23,000 vocalizations.  Within this dataset was also at least 25 different types of call, 20 of which were previously undocumented. 

This result shows that monk seals can create what was deemed as “combinational calls” – in which elemental vocalizations (i.e., single units of sound) are combined together. This is the first time this strategy has been reported in seals and sea lions.  

The team also found a brand new call type – which they have called the “whine”. This is produced when seals are foraging, and is only the second known example of a seal species using vocalizations while pursuing prey – a really neat result. 

To read more about Kirby’s work, check out her previous blogs on soundscapes and biologging tags, and if you want to read about this work in more detail, you can find the article here.