Seapix sonar to bring safety back to the reunion island
Recent years have seen the dramatic rise of shark attacks on the Reunion Island. For the past seven years, over 20 attacks have taken place there, making the small French oceanic island the most dangerous place in the world for shark attacks according to its coastline length. Going through a real crisis, the Reunion Island is now being called “shark island”, “shark aquarium” or “shark attack capital of the world”, nicknames that convey the negative reputation that the island now carries due to those attacks and that led to disastrous economic consequences for the island and its population. To address the situation, the French government and local authorities have thus decided to create a new agency, the CRA (Centre de Ressources et d’Appui à la Gestion du Risque Requin), whose mission is to manage and reduce the shark risk on the Reunion Island. It is to that end that the agency contacted iXblue, with the wish to test SeapiX 3D volumic sonar for the long-range detection of sharks.
“The CRA is looking for new innovative, effective and safe ways to detect sharks before they reach the coasts and become a threat to recreational beach users. The current means of monitoring beaches and surf spots are limited. For instance many of the gillnets used have a significant impact on marine biodiversity and their operating costs are very high. Aerial or subsea surveillances, by drones or freedivers, are limited to good weather conditions and to human perception capabilities. The SeapiX sonar solution would therefore be very complementary to existing methods. This system could be used in any weather and would offer new perspectives for observations. For instance our first simulations showed a detection range of more than 100 meters, when competing systems can only reach 50 meters. Being able to detect sharks at a greater distance would mean more reaction time to alert beach users and surfers, saving lives.”
Olivier Lerda, R&D engineer at iXblue
The challenge was great for the iXblue teams, as sharks are an especially hard specie to detect, their acoustic signature being difficult to confirm due to their lack of swim bladder, an internal gas-filled organ that contributes to the ability of many bony fish to control their buoyancy and that usually increases the amount of acoustic energy returned to the sonar by the target.
“Many thoughts have been put into it in order to maximize our chances of detecting a shark. In the end, we decided that an “FLS” (Forward-Looking Sonar) installation would be best. SeapiX would thus be vertically deployed on the seabed to monitor a horizontal layer of water. This configuration allows the observation of a target during its approach. In addition, the redundancy of detections should allow us to confirm and track the target. An insonification strategy, based on a sequence of narrow and broad transmission beams (for long-distance detection and to cover a larger volume) was also implemented to optimize the monitored area.”
Tests were thus conducted for 2 weeks, off the west coast of the island to assess the efficiency of the SeapiX sonar for such an application. Installed in a forward-looking position on a tripod, 100 meters away from the shores, the SeapiX sonar was able, after a few days, to detect a young 2.7 meters long tiger shark at a distance of 160 meters. A record for the sonar detection of those sharks that do not usually exceeds a few tens of meters
“We are very satisfied by the first results of these tests conducted in partnership with the CRA. Being able to confirm the sharksu2019 acoustic signature at a distance as important as 160 meters, opens up great possibilities for SeapiX. The next step for us is to confirm these capabilities in complex reef areas with very low water levels, chaotic bathymetry with highly reverberant bottom obstacles, and strong surface agitation. We are also looking forward to validating the performance of our new automatic detection algorithm!”