Extraordinary biological discovery off the Sicilian coast. Thanks to the prototype of a submarine observatory developed by the Infn to detect particles coming from the centre of the galaxy, it was possible to discover that there are many more sperm-whales in the Mediterranean than it was thought. An example of the way basic physics research can have extremely important fallbacks on other sciences.
Sperm-whales living in the Mediterranean number in the hundreds, rather than in the tens as it was thought. The discovery took place in the first phase of the Nemo (Nemo-Phase1) experiment that the National Institute for Nuclear Physics put at the disposal of marine biologists in the depths of the sea facing the city of Catania.
The apparatus developed by the Infn allowed biologists from the Interdisciplinary Centre for Bioacustics and Environmental Research of the University of Pavia to listen to voices – the so-called “clicks”– coming from sperm-whales more than 2000 (two thousand) metres deep. In this way, researchers were able to register the passing of at least one specimen every two days during a period of a year and a half. This count leads researchers to believe that hundreds of specimens exist in the Mediterranean.
The recording of sounds through hydrophones in itself was a world-wide first for the depth at which it was carried out and the variety and clarity of the sounds recorded. The voices of dolphins were also recorded.
Nemo is an Infn project – from the National Laboratories of the South, equipped with strong optical sensors for the detection of the feeble light paths produced by neutrinos. It began its activity in January 2005 with the Onde (Ocean Noise Detection Experiment) experimental station, thanks to which researchers were able to monitor the acoustic noise under water in real time. The station is installed at a depth of more than 2000 metres, about 20 km off the coast of Catania.
Nemo-Phase1 is the prototype of the future submarine telescope for high energy neutrinos, which might come from the very core of our galaxy and are able to pass through the earth from one side to the other. Particles whose origin is still mysterious that could bring scientists to discover the source of the quite as mysterious sources of very high energy cosmic rays.
Once completed, the telescope will be made up of 80 towers anchored at a depth of 3500 metres, in the sea off the coast of Cape Passero in Sicily. The towers will be twice as high as the Eiffel Tower.
The discovery of the presence of many sperm-whales in the Mediterranean is an example of the way that basic research in physics can determine important fallbacks for other sciences as well as for culture in general.
Comments from the experts
“There is a strong international competition going on with American research groups who are building a similar apparatus under the ice in Antarctica – explains Emilio Migneco, director of Infn’s National Laboratories of the South– In Europe the European Community co-finances an enormous effort to build the international submarine observatory in the Mediterranean in the near future”.
“From the sounds emitted by the sperm-whales we were able to deduce that some were just passing through, whereas others were probably communicating among themselves on waking up – explains Gianni Pavan, researcher at the Interdisciplinary Centre for Bioacustics and Environmental Research of the University of Pavia – We calculated an average of 3 to 5 specimens every two days. These animals travel at a depth of one thousand metres, where they can capture especially giant clams and they can dive at a speed of 100 metres a minute”.
“It’s great, wonderful news – comments professor Silvio Greco, scientific director at Icram, the Institute for marine research of the ministry for Environment – we thought that sperm-whales had been exterminated in the “spadare” and by deep sea nets. Instead, this research shows that fortunately their presence in the Mediterranean is marked by a significant recovery”.
In a nutshell
• The Mediterranean houses many more sperm-whales that it was thought.
• The discovery was made thanks to a bio-acoustic detector installed by marine biologists on the apparatus of the Infn’s Nemo-Phase1 project.
• Nemo-Phase1 is a prototype of a detector positioned at a depth of more than 2000 metres in the sea off the coast of Catania.
• Nemo-Phase1 is a prototype that will be used to verify the functionality of instruments that will be part of Nemo, a device to detect neutrinos coming from the southern hemisphere, after they have crossed the entire globe.
• Nemo will be positioned 80 km off the Sicilian coast at a depth of 3500 metres and it will occupy a volume of 1 cubic kilometre.
The Nemo project – Technical description
Neutrinos interact very little with matter. Because they have no charge, they are not subject to deflections on behalf of magnetic fields, which would prevent us from tracing back their original direction. However, in order to observe these elusive particles, it’s necessary to build enormous detectors: theoretical estimates indicate that a telescope for high energy neutrinos should have a volume of at least one cubic kilometre (1 km3). Furthermore, in order to be shielded from the shower of cosmic radiation bombarding the earth, these detectors must be installed in extremely protected locations. In a transparent medium such as the water at a great depth or the ice of the Poles, it’s possible to detect the feeble light radiation produced thanks to the Cherenkov effect by the secondary particles (muons) generated by neutrinos when they interact with matter. Because muons move essentially in the same direction as the neutrinos they originate from, by detecting them it’s also possible to determine the direction of the neutrino and so to observe its source. Furthermore, if we position the detector in the depths of the sea (or of Polar ice), matter above it also serves as a shield against the background of cosmic particles, which would “blind” the detector if it were brought to the surface. Therefore, water (or ice), performs three different duties: it acts as a protective shield against cosmic rays, as a target for the interaction between neutrinos and as the transparent medium through which the Cherenkov light travels. In the Nemo-Phase1 project, a test site has been located off the coast of Catania at a depth of more than 2000 metres. Here, last December, a prototype of the future neutrino 1 km3 telescope was installed, composed by a tower shaped mechanical structure, which enables the positioning of optical and environmental sensors in the desired position, and a junction box containing the electronic control system to charge the device and transmit data to the coast. In its final version, Nemo will be composed of as many as 80 towers measuring 750 metres in height (for a total of 5000 light sensors), which will cover a total volume, as calculated, of a cubic kilometre. Its collocation is foreseen about 80 km off Cape Passero (Siracusa), more than 3500 metres deep.
The sperm-whale (Physeter macrocephalus)
It’s a cetacean with a heavyset, square look to it, the male reaches a length of 18 metres and can grow to weigh more than 50 tons, whereas the female grows to a length no greater than 12 metres. It’s an odontocetus, because it has teeth, which make it much more similar to the dolphin than to whales (mystacoceti). Like dolphins, it also has a biosonar and so it’s able to “eco-localize”, in other words to find the right direction, avoid obstacles and find pray through the echo coming back from the signals it emits. The sperm-whale performs long dives, usually around 40-50 minutes long, during which it dives swiftly to depths of about 900-1000 metres and then it swims to hunt cephalopods in the depths. On its return to the surface it usually takes about 10-15 minutes to breathe and stock up on oxygen.
During its dives it emits a series of impulsive signals called “clicks”, whose function is mostly to “eco-localize” in order to receive constant information about the surrounding environment. The series of clicks are divided by brief pauses, or by quick sequences of clicks to “focalise” and capture prey (in analogy to what is done both by dolphins and by bats). It also emits brief rythmic sequences of clicks, called a “tail”, whose structure and rhythm change in the different oceans colonised by these animals. In the Mediterranean the prevailing theme is given by 3 clicks followed by a fourth click later on (3+1 or III-I). On the surface, if they are alone, sperm-whales are essentially silent, but in social aggregates comprising many specimens, males, females and babies, they display a wider inventory of sequences of clicks. The sperm-whale is characterised by the spermaceti, a cylindrical organ made up of bands of muscular and connective tissue containing fatty and oily substances: it’s positioned on the cranium’s frontal bone, and it reaches a length that can be as much as a third of the total body length, which determines the peculiar shape of the cetacean. The spermaceti has a number of functions, one of which is focalising of clicks, like an acoustic lens, analogous to the melon in dolphins. The presence of a unique, asymmetrical spiracle on the left-hand side is also typical of sperm-whales, producing a jet of water inclined forward to the left. The spiracle, connected to the left branch of the respiratory apparatus, is used for breathing, whereas the right-hand side has disappeared because the corresponding branch of the respiratory apparatus transformed into a pneumatic system for the production of clicks.