Depredation - the removal of bait and damage of hooked fish by sharks and cetaceans - is a major issue for pelagic longline fleets, with a negative impact on their economic profitability [1,2] and a risk of mortality to the animals from either retaliation by fishermen or hooking or entanglement in fishing gear . In the BMIS, ‘Depredation Mitigation Devices (DMDs)’ are principally technologies designed to reduce cetacean bycatch through the use of physical barriers to protect target catch.
Cetaceans can be accidentally caught (entangled or hooked) and released injured or dead  during depredation events. Fishers may adopt harmful methods to mitigate depredation, such as killing individuals observed or captured [1,2]. Acoustic technologies have proved largely ineffective in protecting longlines* from depredating cetaceans and weak hooks have not been assessed with regards to post-release mortality . Recent research has been directed at fishing gear technologies designed to physically protect hooked fish from cetaceans. For example, the Paradep project aims to develop a device with three protective aspects: physical (barrier between the fish and the predator), visual (hiding the target catch) and passive acoustic protection (changing the acoustic signature of the target catch).
*Note that anti-depredation pingers produced by Fishtek Marine have had some success in deterring dolphins in a demersal longline fishery in the Gulf of Mexico.
- Anderson RC (2014) Cetaceans and Tuna Fisheries in the Western and Central Indian Ocean. International Pole and Line Foundation, London
Rabearisoa N, Bach P, Tixier P, Guinet C (2012) Pelagic longline fishing trials to shape a mitigation device of the depredation by toothed whales. Journal of Experimental Marine Biology and Ecology 432–433:55–63. doi: 10.1016/j.jembe.2012.07.004
- Fader JE, Elliott BW, Read AJ (2021) The Challenges of Managing Depredation and Bycatch of Toothed Whales in Pelagic Longline Fisheries: Two U.S. Case Studies. Front Mar Sci 8: https://doi.org/10.3389/fmars.2021.618031
- Hamer DJ, Childerhouse SJ, McKinlay JP, et al (2015) Two devices for mitigating odontocete bycatch and depredation at the hook in tropical pelagic longline fisheries. ICES J Mar Sci 72:1691–1705. doi: 10.1093/icesjms/fsv013
Rabearisoa N, Bach P, Marsac F (2015) Assessing interactions between dolphins and small pelagic fish on branchline to design a depredation mitigation device in pelagic longline fisheries. ICES J Mar Sci 72:1682–1690. doi: 10.1093/icesjms/fsu252