Soundscapes of the Mediterranean Sea Episode 2: Cetaceans

Scientists' analyses to explain the excess of human-caused noise in the Mediterranean Sea are striking. In this second episode of the podcast on soundscapes of the Mediterranean Sea, Txema Brotons, scientific director of the organization Tursiops, reveals that noise for cetaceans in marine ecosystem is similar to the discomfort generated trying to have a conversation with someone in a nightclub. 

Some people argue that sound pollution in the Mediterranean should be a matter of interest to everyone, as it greatly impacts cetaceans, and especially at a time when human overreach has brought the planet into a point of environmental stress that gradually deteriorates our habitat. 

So, how can we preserve cetaceans and fight against the climate emergency? In this episode, we answer this question based on the knowledge of scientists who have studied step by step the evolution of these species and the conservation problems that the acoustics produce with sperm whales when they collide with the ships.

Let's begin with a brief review of cetaceans. Cetaceans are mysticetes and odontocetes. The first ones have whales and fin whales as emblematic species. Odontocetes are composed of dolphins, porpoises, belugas, and sperm whales. According to Txema, whales take large amounts of water into their mouths to ingest food. After, they filter it through their baleen plates to retain the nutrients they eat. The sperm whale is the great odontocete cetacean and is currently the largest predator on the planet. 

Some cetaceans live between sixty and seventy years. We should consider that the present sperm whales are the offspring of those persecuted, for example, by the whaling in Japanese waters during the 1950s. 

In this evolutionary and historical context about cetaceans, it is necessary to add that the sense of hearing is all they need to live. And right there is where humans get in the way with activities that introduce excessive noise into the sea that affects their survival. 

Therefore, Michel André, director of the Bioacoustics Applications Laboratory at the Polytechnic University of Catalonia, mentions that the first thing to understand is that noise propagates five times faster in water than in air. In the air, it is 340 meters per second. In the sea, it is 1.5 kilometers per second. The cetaceans that receive this information have a sensitivity adapted to capture this sound underwater. According to Michel André, this marine species can hear sounds people do not hear. While humans have a limited hearing capacity window of 20 hertz to 20 thousand hertz, cetaceans can register from a few Hertz to 150 -200 thousand Hertz. 

Cetaceans’ conservation is essential to face the climate emergency

Txema explains that atmospheric CO₂ is captured by phytoplankton photosynthesis. These microscopic organisms that live in watery environments need nutrients, like iron, to grow, which is scarce in the sea, adds Txema. 

The cycle of nature is perfect. Sperm whales eat at depth and excrete at the surface. Because of their diet, their feces are rich in iron. What are sperm whales doing? They support the growth of phytoplankton, increasing the CO2 uptake capacity of the seas and oceans. In other words, the sperm whale acts directly to prevent global warming.

To conclude, the second episode of the podcast discusses the issue of human-caused noise in the Mediterranean Sea and its impact on cetaceans, particularly sperm whales. We also provide information on the evolutionary and historical context of cetaceans, their hearing sensitivity, and the role of sperm whales in supporting the growth of phytoplankton and preventing global warming. 

We invite you to listen to this podcast episode on cetaceans in the series on the Soundscapes of the Mediterranean Sea. You can learn more about these magnificent animals and their sounds, as well as the impact of human-caused noise on their survival. 

Listen to the second episode in English: 

And in Spanish: 

• Listen to Episode 1 of this podcast series. 

This story was produced with support from Internews' Earth Journalism Network. It was first published in Carijonas on 29 March 2023 in Spanish; this version has been adapted by EJN's Mediterranean Media Initiative.

Banner image: A whale swimming past swimmers, Cannes, France, July 2017 / Credit: Marvin Meyer via Unsplash.