The first depredation mitigation device trials were carried out off Sète, south of France, on August 02 and 07, 2019. Researchers and engineers from IRD, IFREMER and SATIM were involved in those trials, which took place onboard an IFREMER research vessel. This survey aimed at assessing the behaviour of two prototypes (named A and B) in shallow waters. A 35m long mainline was suspended in the water by 6 floats to simulate a pelagic longline. Eight branchlines equipped with eight A and B devices were attached to the mainline. European bass and hake were hooked to each branchline to simulate the captured fish. Once the whole mainline was set, two divers sequentially pulled on the branchlines to simulate a biting fish and trigger each device. Waterproof cameras were used to record the behaviour of each device, from its triggering to the moment it slid down and protected the fish. A total of five line settings were carried out, corresponding to 40 device triggerings.
Configuration of the experimental longline equipped with 4 “A prototypes” and 4 “B prototypes”
RV Chlamys
Diver swimming towards the experimental line
“A” device:
The A device is made up of a metallic mobile support, on which four linen veils are attached. The case, attached to the branchline snap with a snap hook, is designed to store the veils. The nylon branchline is inserted inside the device. When a fish is hooked, a metallic element presses down on the mobile support and triggers the device. This releases the mobile support which slides down the branchline. Then, the veils are deployed around the fish and protect it from predators.
“A Device”
“B” device:
The B device is made up of a cylindrical hollow case attached to the branchline snap. The mobile support is inserted in that case, and is made up of four compartments dedicated to store the veils. The four linen veils are attached at the base of the mobile support. The branchline is inserted into the case and the mobile support. When a fish is hooked, a metallic element presses down on the base of the mobile support and triggers the device. This releases the mobile support which slides down the branchline. Unlike the A device, the veils are still stored in their storage compartment when the B device is triggered. Thanks to water currents or fish movements, the veils exit their storage space, are deployed around the fish and protect it from predators.
“B Device”
At the end of the survey, recorded movies were used to assess the device behaviour. Several technical factors were analyzed for both devices: setting behaviour, correct functioning of the triggering system, veils deployment, fish protection, hauling behaviour, storage system. We also wanted to assess how quick and easy the device slid down the branchline.
Those analyses resulted in the following satisfaction table:
Evaluation of the satisfaction level regarding the behaviour of PARADEP (1: very low level, 2: low level, 3: medium level, 4: high level, 5: very high level)
These first results gave valuable insights to improve the PARADEP device. A second survey will be implemented at the end of 2019 (or the beginning of 2020) to assess the behaviour of the modified devices. This will lead to the mass production of the depredation mitigation device, which will be tested onboard commercial pelagic longliners in Reunion Island from March 2020.
June 11 – 19, 2019: Marc SORIA, our acoustic engineer involved in the PARADEP project, undertook an acoustic survey onboard the Vetyver 6 during a commercial fishing campaign. That 16 m long commercial pelagic longliner belongs to the fishing company and project partner ENEZ DU. The goal of that survey was to improve our knowledge about the behaviour of toothed whale species involved in depredation and evolving in the vessel vicinity. During each fishing operation, 24 accelerometers, 6 hydrophones and 2 underwater cameras were set. Hydrophone allows detection of sounds emitted by marine mammals, while accelerometer provides information about the way they move and their behaviour. Collected data will allow to assess false killer whales and short-finned pilot whales’ presence and behaviour during depredation events. In the end, we expect to get new insights into toothed whale depredation process: preferential period of the day for depredation, cues that may lead to line detection and capture detection.
ST300HF hydrophone 200 mm L * 60 mm D (A), PARALENZ camera with snap 116 mm L * 38 mm D (B), DEEPG+ accelerometer (C)
Survey monitoring
The fishing trip took place from June 11 to June 19, 2019, in a fishing area located 100 miles south of La Réunion Island. Six fishing operations were undertaken, and the aforementioned material was deployed during each longline setting. A total of 840 hooks (baited with squid) were set.
Fishing area
Both underwater cameras were deployed on the mainline, at the beginning of the line. The hydrophones were deployed on the first six floatlines and the accelerometers were set on both sides of the hydrophones.
Line setting
Camera immersion
Underwater view recorded by one camera
Results
Catch mainly included yellowfin, albacore, bigeye tunas and swordfish. About 600 kg of fish were caught each day. Unfortunately, neither toothed whale nor toothed whale depredation event was recorded during the survey.
Captures of tuna and swordfish
Tuna depredated by shark
Data processing is currently ongoing. First, we will sample acoustic data to detect potential toothed whale clicks. Then, we will analyze the accelerometers data to detect capture events and potential predator movements in the line vicinity. Despite the fact that no toothed whale depredation event was witnessed, we will analyze the recorded data anyway. Indeed, sounds emitted by marine mammals evolving near the line may have been recorded. Sounds emitted by tuna and swordfish may have also been recorded.
The report will be available soon.
13-14/06/2019 : Shooting of a documentary about the conception of the depredation mitigation device
During a work meeting with the SATIM team (Niort, France) in charge of the device conception, Luc MARKIW (IRD Images) recorded the different steps of the prototype machining. He also interviewed some of the actors involved in the project. Those shootings will be used in a general documentary relating the genesis of PARADEP, from its conception to the final tests onboard commercial pelagic longliners.
06/10/2019: Preliminary acoustic survey onboard a commercial pelagic longliner
Marc SORIA, acoustical engineer involved in the PARADEP project, will be onboard the Vétyver 6 (ENEZ DU fishing company) during a commercial fishing trip which will last 15 days. He will deploy several hydrophones, accelerometers and cameras along the longline, in order to record acoustic signals emitted by marine mammals evolving near the fishing gear. Acoustic recordings will be associated with visual observations when possible. This will allow to associate the acoustic signals with specific marine mammal species.
The acoustic material will be deployed again during the commercial trips aiming at testing the depredation mitigation devices. The general objective of those acoustic recordings is to improve our knowledge about the depredation process. They will also allow a better understanding of the marine mammal acoustic behavior during depredation events.
4/8/2019 : Start of the internship of Sara BOUTAAM (MSc Mechanics of composite structures: aeronautics and eco-design, Paris Nanterre University).
Title: Design of a toothed whale depredation mitigation device for pelagic longline fisheries: food for thought
Internship content:
- Bibliography
- Design of the prototypes
- Field tests if possible
Supervisors: N. Rabearisoa, P. Bach, P. Vidal (Energetics Mechanics Electromagnetism Laboratory , Paris Nanterre University), E. Valot (Energetics Mechanics Electromagnetism Laboratory, Paris Nanterre University).
Duration: 5 months
Host laboratories: LEME Paris Nanterre and IRD MARBEC Sète
Objective: Design of a physical depredation mitigation device
This innovative device will have three protective skills: physical (barrier between the fish and the predator), visual (hiding of the fish) and passive acoustic (modification of the fish acoustic signature).
Service provider: SATIM Exploitation (http://www.satim.fr/satim-exploitation.php)
