Shielding Fish to Protect Whales and Fishers Income

Some toothed whale species have gotten used to stealing or damaging fish that have been captured by the fishing equipment of fishers. This stealing is called depredation, and it is a problem for both fishers and toothed whales in all the oceans of the world. Fishers lose their catch and must work harder, and the whales can get injured and forget how to hunt. It is important to develop a solution to prevent toothed whales from stealing fish captured by fishers. Our group of scientists is developing a system that can protect captured fish from being stolen. Basically, our innovation is like Spider-man© throwing a spiderweb over the fish, to hide them from toothed whales! In the near future, we are hopeful that this system will both help the fishers by protecting their catch and help to protect toothed whales.


WHAT IS DEPREDATION AND WHY IS IT A PROBLEM?
You probably already know that fish are an important part of the human food supply. But did you know that toothed whales have learned to

TOOTHED WHALES
A group of marine mammals, including killer whales or dolphins, that have pointy teeth and feed on fish or squids. steal fish from fishers in all the oceans of the world? When fish are captured in fishing gear, some species of toothed whales have gotten used to eating them before the fish are hauled onto the fishing boat. This is called depredation. Depredation by toothed whales happens DEPREDATION The act of damaging or stealing plants or animals grown or bred by humans. For instance, coyotes or foxes sneaking into a farm to eat chickens is depredation.
frequently, and it is bad for both the toothed whales and the fishers [ , ].
Why is depredation bad for toothed whales? Well, instead of hunting wild fish as they should naturally do, these whales would rather eat fish that have already been caught. By doing so, they save energy and easily get a large amount of nutritious food. Depredation can lead whales to forget their own natural hunting strategies, and they might lose the ability to obtain food by themselves. Toothed whales can also be injured by fishing gear-they can get entangled or hooked as they try to remove the fish. All marine mammal species are classified as endangered, and several laws exist to protect these species from human threats, including threats posed by the fishing industry. This is one reason depredation should be prevented.
In terms of the fishers, they cannot sell damaged fish, so to replace the fish lost to depredation, they must do more fishing! This is a waste of time and money because the fishers must use more fuel, deploy more hooks, invest more hours, and fix the equipment damaged by toothed whales. Depredation also has consequences for the total number of fish available to be harvested as human food. Fish are a limited resource. Depredated fish are not counted by the fishers and therefore are not reported in fishery statistics. Consequently, fishery scientists might incorrectly calculate how many fish are left to catch in the ocean (Figure ).

Figure
Depredation a ects toothed whales, fishers, and captured fish. Depredation changes the hunting strategies of toothed whales and these animals can also get injured when they try to steal the hooked fish. Fishers lose money and have to work harder to compensate for their damaged catch. Finally, depredation impacts fish species because, since depredated fish are not counted in fisheries statistics, the number of fish left to catch in the ocean is calculated incorrectly.

WHAT KIND OF FISHING DO WE STUDY?
For our work, we focus on a fishing technique called drifting longline fishing. Fishers use this method to catch large fish such as tuna or at the surface thanks to large buoys attached at regular intervals. The mainline, which can be as long as km, is attached to vertical secondary lines called branchlines, each one with a hook at its end.

BRANCHLINE
A vertical secondary line attached at regular intervals to the mainline, with a baited hook at its end. Fishers can set up to , branchlines on the same mainline to capture fish.
Each hook is baited with a squid or a mackerel. The branchlines are left to hang down in the water to attract and catch fish ( Figure A). This entire fishing apparatus is called a longline. Fishers can set up to , hooks on the same longline. The longline is left to drift for about -h before being hauled onboard to harvest the captured fish.

WHICH TOOTHED WHALES ENGAGE IN DEPREDATION?
In tropical waters, two species of toothed whales-the false killer whale and the short-finned pilot whale-are commonly involved in depredation of fish caught on longlines ( Figure B). Can you guess how big tuna and swordfish captured by longliners are? Tuna can exceed one meter in length, and swordfish can measure -m in length. However, false killer whales and short-finned pilot whales can be up to m long. When depredating a fish, they tear the flesh o , leaving only the fish's head on the hook ( Figure A). whales and other animals, like bats, use this hunting technique to locate and identify their prey, based on the specific echoes that return to them. Toothed whales use echolocation to spot the hooked fish, kids.frontiersin.org June | Volume | Article | and the noises of the boat in the distance also attract the whales. Since hooked fish cannot swim away, it is very easy for the whales to feed on them: it is like a ready-to-eat meal in an all-you-can-eat restaurant! It is so easy that toothed whales sometimes swim along the mainline and steal every single captured fish, making the fishers to feel desperate.

PARADEP: A POTENTIAL SOLUTION
So far, several techniques have been tested worldwide to decrease depredation, but none of them work very well [ -]. We run a project called PARADEP , to find an innovative way to reduce depredation https:// paradep.com/en by toothed whales. The aim of the project is to design a shield that can hide and protect the captured fish. How does it work? First, picture Spider-man © : his super power allows him to shoot an adhesive spiderweb through a small barrel located on his wrist, right? Our device is similar to this barrel. Two protection nets (which look like Superman's © cape) are stored inside a small case. These cases are attached to the tops of every branchline. When the fish bites the bait and pulls on the hook, the case opens. Then, the protection nets are ejected, slide down the branchline, and wrap the fish up. Then the fish is protected by a shield, as if it were wearing an invisibility cloak. The net shield makes it harder for toothed whales to see and eat the fish, so the net avoids whales from depredating the fish until the line is hauled back onboard. This way, the fisher can harvest undamaged fish, even if toothed whales are swimming near the boat (Figure ). Our device will keep fishers from both losing income and working overtime to compensate for the loss of fish. The device is reusable, so it is environmentally friendly and economically attractive for fishers. It will also help protect the toothed whales, because it will reduce their risk of injury and they will have to use their natural hunting skills again.

TAKE-HOME MESSAGE
Depredation of fish caught by drifting longliners causes conflicts between fishers and toothed whales. This interaction needs to change, so that fishers and toothed whales can share the same feeding/fishing grounds without harming each other. By creating a shield around a hooked fish until it is hauled onboard, the PARADEP device may be the solution we are looking for, both for protecting toothed whales and preventing fish from being stolen. We are working with fishers because they want something to help them decrease depredation. They are playing an important role in testing the PARADEP device.
After several months of PARADEP testing and collection of feedback from the fishers who are using it, we will know whether PARADEP works well-enough to help reduce depredation by toothed whales throughout the world's oceans.

ACKNOWLEDGMENTS
We thank the European Maritime and Fisheries Fund for funding the PARADEP project. The project was made possible due to the involvement of Auriane Serval, Chloé Yven, Marc Soria, Nicolas Guillon, Evgeny Romanov, and all those who took part in the fieldwork: thanks to all of them. Additionally, the authors would like to thank Yona Bodin for her feedback and her constructive comments. Our appreciation also goes to Pr Frédérique Carcaillet for her helpful comments to improve the manuscript. Finally, we are very grateful to the young reviewers, their mentors and the journal Editors for all their useful feedbacks.
. Toothed whale and shark depredation indicators: a case study from the Reunion Island and seychelles pelagic longline fisheries. PLoS ONE.
. Assessing interactions between dolphins and small pelagic fish on branchline to design a depredation mitigation device in pelagic longline fisheries. ICES J. Mar. Sci.

CONFLICT OF INTEREST:
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
COPYRIGHT © Rabearisoa, Arnau, Bodin, Hanse, Portalez and Bach. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

INTERNATIONAL SCHOOL OF BERGEN, AGE:
The graders at the International School of Bergen form a dynamic group with highly diverse international backgrounds. They are interested in learning the scientific method and sustainability, but also have a great artistic talent.

MATÍAS, AGE:
I love playing music and doing magic tricks, I like science and my favorite subject is physics.

ALICE ARNAU
Alice Arnau is a master's student at the science faculty of the University of Montpellier. After graduation, she will work in the complex field of environmental management. She will especially dedicate herself to answering questions related to human coexistence with other living organisms (depredation being one of many examples).

MANON BODIN
Manon Bodin is a master's student at the science faculty of the University of Montpellier. She is willing to work in a field that allows her to link science and video games, so that everyone, including children, can learn to like biology.

CONSTANCE HANSE
Constance Hanse is a master's student at the science faculty of the University of Montpellier. She likes to share her knowledge and teach ecology and biology concepts in a way that makes them easy to understand.

MARIN PORTALEZ
Marin Portalez is a master's student at the science faculty of the University of Montpellier. He is majoring in scientific mediation and communication for school-aged audiences. He is passionate about science, especially about the biology and ecology of Mediterranean ecosystems. He is also interested in arts. He uses his skills in both science and arts to run several scientific projects.

PASCAL BACH
Pascal Bach is currently a researcher at the French Institute of Research for Sustainable Development. He has been working for years as a fishery ecologist involved in research projects with scientific partners mainly based in the south west Indian Ocean. The theme of his research is ecosystem-based fishery management, and he is developing ways to decrease the negative impacts of fisheries on non-targeted species. He enjoys meeting the other people involved in fisheries management over a glass of wine, to make the discussions more pleasant.