In the waters off Toulon, in the abyss of the continental shelf’s canyons, sperm whales hunt squid. Man’s increasingly apparent presence troubles these huge sounders of the depths and could cause an ecological and economic disaster… for man.
Hervé Glotin is a professor at the University south-Toulon-Var (USTV) and Mixed Research Unit, Sciences and Information Systems. His passion: the deep sea trenches that run along the continental plateau.
Off the coast of Toulon, where the continental slope plunges quickly to a depth of more than 1,000 meters, scientists have dipped their electronic ears.
“Sphyrna Odyssey is a two-month adventure during which we release a surface drone equipped with an acoustic antenna with five hydrophones and a very high frequency and high velocity sound card developed by the University of Toulon,” explains the researcher. “This allows us to detect these huge echolocating hunters that only surface for 10% of their lives, and determine the number of individuals per km3. “
The purpose of the mission is to discover what whales do, especially sperm whales and beaked whales, during the 90% of their life spent underwater, which we know very little about.
We can now observe life in the abyss, partly thanks to the Sphyrna drone, developed by a company called Sea Proven.
Probes over 1,000 meters deep
What we already knew is that during its 45 minute sound probes, a sperm whale hunts several hundred kilos of squid.
These deep sea cephalopods, that we also know little about, are rarely caught by fishermen, but they are the favorite prey of the echolocating whales.
“By listening to sperm whales as they hunt, we can identify the squid reserves” explains Hervé Glotin. “Thanks to the recorded sonar, tracking from initial detection to final approach, we are able to count the number of prey caught by the sperm whale. The silence that follows means they are eating. ”
The researcher also moored a subsurface Bombyx buoy at 45 meters below the surface, which allowed him to identify, over a period of 80 days, close to 100 passages; however, he wasn’t able to identify how many individuals live in the zone. He estimates the number of sperm whales to be about one hundred. These super-predators of the abyss play an essential role, as much on the ecological level as on the economic level. “If we reduce sperm whale hunting, or if we eliminate it, we interrupt the trophic chain,” worries the researcher. “The trophic chain is a food chain in which each organism eats the ones from the level below it. ”
Ecological and economic catastrophe
In the Mediterranean, and especially in coastal areas, the sperm whale is at the top of this chain… above squid. The cetacean’s disappearance would lead to the emergence of a new food chain, with the fish-eating cephalopod at the top. This new chain would be economically catastrophic for the fishing industry.
But what interests the researcher most is finding out whether human activities influence marine mammal’s behavior. “It’s clear that there is a risk of injury through collision with these animals that are vulnerable when they are resting or breathing on the surface,” continued Hervé Glotin. “They need this rest and a calm area on the surface to effectively send out sound probes. It is also possible that the permanent noise in the area disrupts how they detect and approach prey in water layers as much as 500-800 meters deep.”
With an increasing number of boats during the season, and ever bigger cruise ships, we are heading for certain disaster. The aquatic sound volume is more and more saturated. Regulations on the speed and density of boats must be established.
But most importantly, we must change our habits and think about silent propulsion. Solutions do exist. Electric motors perform better and better. Autonomy has made great strides thanks to hydrogen.
Energy Observer is navigating proof of this.