How is sound used to mitigate marine mammal/fisheries conflicts?

Pingers: Reducing the Risk of Entanglement in Gillnet Gear

Entanglements in fisheries is a global problem that affects at least 40 species of cetaceans. World-wide, over 300,000 cetaceans are estimated to be incidentally caught in fishing gear each year. Some species, such as the Vaquita, are threatened with extinction due to entanglement-related deaths.

Small coastal cetaceans like the vaquita, and their northern relatives, the harbor porpoise, are vulnerable to entanglement primarily due to overlap between their habitat and gillnet fisheries. Traditionally, gillnet gear consists of nylon nets that are suspended in the water column. Marine mammals may not detect the fine-mesh nets in time to avoid a collision. Cetaceans may also become entangled due to opportunistic feeding on fish that are already captured in the nets. As gillnet operations continue in areas inhabited by coastal cetaceans, methods to reduce entanglement risks are needed.

One technique developed to reduce cetacean bycatch is to attach acoustic “pingers” to gillnet gear. Pingers emit pulsed, high frequency signals that alert animals to gear in the water column. Cetaceans may use echolocation to investigate the pinger sound source and avoid the gear, or they may simply be startled by the sound and avoid the area.

Commercially available pingers broadcast short duration (<1 s) signals at 10 kHz with source levels of 132 underwater dB. It is critical that pingers do not deter fish targeted by the gear, and hence, frequencies should be set outside the auditory range of fish (>2 kHz). It important, and also challenging, to deter pinnipeds (seals and sea lions) from gillnets. Pinger signals may result in the “dinner bell” effect, where sound acts as an attractant to a food source, and in this case, would put seals and sea lions at risk of entanglement in gillnet gear.

Research suggests the effectiveness of pingers may vary widely between species, fishing areas, season, and fisheries. Both field and laboratory studies have shown that some cetaceans, such as the harbor porpoise, Franciscana dolphin, Ganges River dolphin, and several species of beaked whales, avoid nets equipped with acoustic alarms^[1]Bordino, P., Kraus, S., Albareda, D., Fazio, A., Palmerio, A., Mendez, M., & Botta, S. (2002). Reducing incidental mortality of franciscana dolphin pontoporia blainvillei with acoustic warning devices attached to fishing nets. Marine Mammal Science, 18(4), 833–842. https://doi.org/10.1111/j.1748-7692.2002.tb01076.x^[2]Carlström, J. (2002). A field experiment using acoustic alarms (pingers) to reduce harbour porpoise by-catch in bottom-set gillnets. ICES Journal of Marine Science, 59(4), 816–824. https://doi.org/10.1006/jmsc.2002.1214^[3]Barlow, J., & Cameron, G. A. (2003). Field experiments show that acoustic pingers reduce marine mammal bycatch in the California drift gill net fishery. Marine Mammal Science, 19(2), 265–283. https://doi.org/10.1111/j.1748-7692.2003.tb01108.x^[4]Carretta, J. V., Barlow, J., & Enriquez, L. (2008). Acoustic pingers eliminate beaked whale bycatch in a gill net fishery. Marine Mammal Science https://doi.org/10.1111/j.1748-7692.2008.00218.x^[5]Kolipakam, V., Jacob, M., Gayathri, A., Deori, S., Sarma, H., Tasfia, S. T., Rokade, A., Negi, R., Wakid, A., & Qureshi, Q. (2022). Pingers are effective in reducing net entanglement of river dolphins. Scientific Reports, 12(1), 9382. https://doi.org/10.1038/s41598-022-12670-y. However, mixed results have been cited for the bottlenose dolphin, and the striped dolphin has shown no reaction to pingers^[6]Cox, T. M., Read, A. J., Swanner, D., Urian, K., & Waples, D. (2004). Behavioral responses of bottlenose dolphins, Tursiops truncatus, to gillnets and acoustic alarms. Biological Conservation, 115(2), 203–212. https://doi.org/10.1016/S0006-3207(03)00108-3^[7]Kastelein, R. A., Jennings, N., Verboom, W. C., de Haan, D., & Schooneman, N. M. (2006). Differences in the response of a striped dolphin (Stenella coeruleoalba) and a harbour porpoise (Phocoena phocoena) to an acoustic alarm. Marine Environmental Research, 61(3), 363–378. https://doi.org/10.1016/j.marenvres.2005.11.005. Lower frequency pingers have also been tested with baleen whales, such as humpback whales, with inconclusive results^[8]Harcourt, R., Pirotta, V., Heller, G., Peddemors, V., & Slip, D. (2014). A whale alarm fails to deter migrating humpback whales: An empirical test. Endangered Species Research, 25(1), 35–42. https://doi.org/10.3354/esr00614. Despite many unknowns about the short- and long-term effects of pinger use, they are nonetheless recommended by the International whaling Commission (IWC) as a means to reduce bycatch of harbor porpoise and other small cetacean species.

Acoustic Deterrent Devices (ADDs): Mitigating Aquaculture/Pinniped Conflicts

Marine (and freshwater) aquaculture is one of the fastest growing food industries (global production ~$70 billion). It is estimated that 50% of seafood is produced by aquaculture. Fish farms, as potential sources for food, attract marine mammals, predominantly pinnipeds (seals and sea lions), which will bite fish through the nets enclosing the fish pens. Pushing up against and biting at aquaculture nets puts seals and sea lions at risk of entanglement. To prevent attacks, some farm managers have illegally shot seals and sea lions. Other marine mammal species are also known to interact with fish hatcheries, such as humpback whales in Alaska, which have been observed feeding on juvenile salmon near hatchery release sites^[9]Chenoweth, E. M., Straley, J. M., McPhee, M. V., Atkinson, S., & Reifenstuhl, S. (2017). Humpback whales feed on hatchery-released juvenile salmon. Royal Society Open Science, 4(7), 170180. https://doi.org/10.1098/rsos.170180.

Acoustic Deterrent Devices (ADDs, also known as Acoustic Harassment Devices [AHDs]) are used globally to deter pinnipeds from aquaculture pens. They are also used in offshore wind farm construction prior to pile driving activities to deter species such as harbor porpoise from the area^[10]Voß, J., Rose, A., Kosarev, V., Vílela, R., Van Opzeeland, I. C., & Diederichs, A. (2023). Response of harbor porpoises (Phocoena phocoena) to different types of acoustic harassment devices and subsequent piling during the construction of offshore wind farms. Frontiers in Marine Science, 10, 1128322. https://doi.org/10.3389/fmars.2023.1128322. Harbor porpoise have very high frequency hearing sensitivities and overlap in areas of active wind farm construction.

ADDs emit intense (source levels up to 195 underwater dB), high frequency, pulses (frequency range of 10-40 kHz, main energy between 10 and 14 kHz). Most fishes do not hear well at these frequencies and are not affected by ADDs. The devices are attached to aquaculture cages underwater and can be set to run continuously. A variety of commercially available ADD types exist, which differ in their acoustic characteristics (e.g., frequency range, amplitude, and duty cycle).

There are substantial concerns with ADD usage and their long-term effectiveness in preventing pinniped interactions remains inconclusive^[11]Götz, T., & Janik, V. (2013). Acoustic deterrent devices to prevent pinniped depredation: Efficiency, conservation concerns and possible solutions. Marine Ecology Progress Series, 492, 285–302. https://doi.org/10.3354/meps10482. There is potential for pinnipeds to become habituated to the ADD sounds, causing a decrease in deterrence, or the animals may associate the sounds with a food source (the “dinner bell” effect). Prolonged exposure to ADD sounds may also cause temporary and/or permanent hearing threshold shifts (TTS or PTS) in target pinnipeds, as well as other, non-target marine mammals in the area. For example, a harbor porpoise in captivity was exposed to an artificial ADD signal with a peak frequency of 14 kHz. A significant TTS response was found, with a TTS onset of 142 dB re 1 μPa2s at 20 kHz and 147 dB re 1 μPa2s at 28 kHz^[12]Schaffeld, T., Ruser, A., Woelfing, B., Baltzer, J., Kristensen, J. H., Larsson, J., Schnitzler, J. G., & Siebert, U. (2019). The use of seal scarers as a protective mitigation measure can induce hearing impairment in harbour porpoises. The Journal of the Acoustical Society of America, 146(6), 4288–4298. https://doi.org/10.1121/1.5135303. Harbor porpoise, dolphin, and killer whale densities have decreased in areas near active ADDs^[13]Johnston, D. W. (2002). The effect of acoustic harassment devices on harbour porpoises (Phocoena phocoena) in the Bay of Fundy, Canada. Biological Conservation, 108(1), 113–118. https://doi.org/10.1016/S0006-3207(02)00099-X. Some researchers consider ADDs a chronic source of anthropogenic sound, especially when they are used at multiple sites and for extended periods. In some locations, such as British Columbia, Canada, the use of ADDs is prohibited.

One key factor in mitigation fisheries/marine mammal conflicts is the motivation of an animal to keep it in an area. The effectiveness of pingers and/or ADDs is affected by individual motivation to find food as well individual and species-specific hearing characteristics. As an example, an animal that is highly motivated to find food, may ignore a pinger, or some animals may be hearing impaired and not able to detect a pinger. Pinnipeds and other marine mammals that actively feed from net pens or set nets have a heightened benefit (e.g. easy access to a food source) which outweighs avoidance^[14]Schakner, Z. A., & Blumstein, D. T. (2013). Behavioral biology of marine mammal deterrents: A review and prospectus. Biological Conservation, 167, 380–389. https://doi.org/10.1016/j.biocon.2013.08.024.

Passive Acoustics: Monitoring and Mitigating Toothed Whale interactions with Longline Fishing Gear

Longlining is a commercial fishing method that uses horizontal lines, 1.6- 4.8 km (1-3 miles) in length, from which shorter lines, with baited hooks, are hung. Gear can be set on the seafloor (demersal longlining) or through the water column (pelagic longlining). Once set, the longline is left to left in the water from one hour to a day or more before it is hauled back onto the boat and fish are harvested. Toothed whales, including sperm whales, killer whales, false killer whales, pilot whales, and a variety of dolphin species, are attracted to longlines because of the lower energetic cost of foraging on bait and/or hooked catch on the line. Researchers have documented that some killer whales travel hundreds of kilometers between fishing vessels for an easy, longline meal^[15]Cieslak, M., Tixier, P., Richard, G., Hindell, M., Arnould, J. P. Y., & Lea, M.-A. (2021). Acoustics and photo-identification provide new insights on killer whale presence and movements when interacting with longline fisheries in South East Australia. Fisheries Research, 233, 105748. https://doi.org/10.1016/j.fishres.2020.105748. Some satellite-tagged false killer whales showed directed movements toward fishing gear being hauled from as far as 100 km away^[16]Anderson, D., Baird, R. W., Bradford, A. L., & Oleson, E. M. (2020). Is it all about the haul? Pelagic false killer whale interactions with longline fisheries in the central North Pacific. Fisheries Research, 230, 105665. https://doi.org/10.1016/j.fishres.2020.105665. Data from tagged sperm whales suggest that every hour the whales spend removing fish from longline gear is equivalent to three hours of natural foraging effort in terms of feeding success^[17]Mathias, D., Thode, A. M., Straley, J., Calambokidis, J., Schorr, G. S., & Folkert, K. (2012). Acoustic and diving behavior of sperm whales ( Physeter macrocephalus ) during natural and depredation foraging in the Gulf of Alaska. The Journal of the Acoustical Society of America, 132(1), 518–532. https://doi.org/10.1121/1.4726005. In the eastern Gulf of Alaska, sperm whales remove hooked sablefish from the longline gear before it is retrieved, stripping a quarter or more of the total fish catch from each haul. Sablefish are the highest valued finfish in Alaskan commercial fisheries. The fishery has an estimated annual value of over $100 million (U.S. dollars) with fishermen landing an average of 13,000 metric tons of sablefish each year. Thus, the sperm whale depredation, worth about $25 million a year, is significant for the fishery and also presents a hazard to the whales themselves.

Growing concern for increased fishing-related risks and fisheries losses have prompted more research on toothed whale/ longline gear interactions. False killer whales interact with a number of pelagic longline fisheries across the globe, including the Hawai‘i-based, deep-set longline fishery that targets bigeye tuna. Estimated fishery-related mortality and serious injury of this species has repeatedly exceeded allowable levels under the U.S. Marine Mammal Protection Act^[18]Carretta, J. V., Oleson, E. M. (Erin M., Baker, J. D., Weller, D. W., Lang, A. R., Muto, M. (Marcia), Hanson, B., Orr, A. J., Huber, H. R., Lowry, M. S., Barlow, J., Moore, J. E., Lynch, D., Carswell, L., & Brownell, R. L. (2017). U.S. Pacific marine mammal stock assessments, 2016. https://doi.org/10.7289/V5/TM-SWFSC-577. Understanding behavioral characteristics of marine mammal/fisheries interactions is important to mitigating potential impacts. Passive acoustics has become an important tool in understanding the rate of depredation – characteristic echolocation foraging sounds and periods of silence following them have been used as a proxy to quantify feeding events ^[19]Thode, A. M., Wild, L., Mathias, D., Straley, J., & Lunsford, C. (2014). A comparison of acoustic and visual metrics of sperm whale longline depredation. The Journal of the Acoustical Society of America, 135(5), 3086–3100. https://doi.org/10.1121/1.4869853^[20]Thode, A., Mathias, D., Straley, J., O’Connell, V., Behnken, L., Falvey, D., Wild, L., Calambokidis, J., Schorr, G., Andrews, R., Liddle, J., & Lestenkof, P. (2015). Cues, creaks, and decoys: Using passive acoustic monitoring as a tool for studying sperm whale depredation. ICES Journal of Marine Science, 72(5), 1621–1636. https://doi.org/10.1093/icesjms/fsv024^[21]Richard, G., Bonnel, J., Beesau, J., Calvo, E., Cassiano, F., Dramet, M., Glaziou, A., Korycka, K., Guinet, C., & Samaran, F. (2022). Passive acoustic monitoring reveals feeding attempts at close range from soaking demersal longlines by two killer whale ecotypes. Marine Mammal Science, 38(1), 304–325. https://doi.org/10.1111/mms.12860. Acoustics can also be used to understand the timing and movement of toothed whales in their environment. Using bioacoustics tags, researchers found depredating sperm whales dive differently and are more acoustically active than under natural foraging conditions^[22]Mathias, D., Thode, A. M., Straley, J., Calambokidis, J., Schorr, G. S., & Folkert, K. (2012). Acoustic and diving behavior of sperm whales ( Physeter macrocephalus ) during natural and depredation foraging in the Gulf of Alaska. The Journal of the Acoustical Society of America, 132(1), 518–532. https://doi.org/10.1121/1.4726005. Lastly, line vibrations associated with depredation events can also be detected and used to quantify depredation encounters. For example, for false killer whales, the act of plucking bait off a hook generated a distinctive 15 Hz line vibration^[23]Thode, A., Wild, L., Straley, J., Barnes, D., Bayless, A., O’Connell, V., Oleson, E., Sarkar, J., Falvey, D., Behnken, L., & Martin, S. (2016). Using line acceleration to measure false killer whale ( Pseudorca crassidens ) click and whistle source levels during pelagic longline depredation. The Journal of the Acoustical Society of America, 140(5), 3941–3951. https://doi.org/10.1121/1.4966625.

Acoustic cues have been implicated in attracting cetaceans to longline fishing gear^[24]Richard, G., Samaran, F., Guinet, C., & Bonnel, J. (2021). Settings of demersal longlines reveal acoustic cues that can inform toothed whales where and when to depredate. JASA Express Letters, 1(1), 016004. https://doi.org/10.1121/10.0003191. Propeller cavitation noise produced as vessels cycle their engines on and off during hauling operations appears to cue sperm whales to bottom-set longlines in the Gulf of Alaska^[25]Thode, A., Straley, J., Tiemann, C. O., Folkert, K., & O’Connell, V. (2007). Observations of potential acoustic cues that attract sperm whales to longline fishing in the Gulf of Alaska. The Journal of the Acoustical Society of America, 122(2), 1265–1277. https://doi.org/10.1121/1.2749450. This distinct sound is estimated to be detectable above ambient sound up to 8 km from the vessel. False killer whales off Hawai’i also appear cued to a signal generated by fishing vessels when hauling in their gear. Fifty-seven percent of false killer whale acoustic detections occurred when the fishers were hauling their tuna longline gear back on board the vessel^[26]Bayless, A. R., Oleson, E. M., Baumann-Pickering, S., Simonis, A. E., Marchetti, J., Martin, S., & Wiggins, S. M. (2017). Acoustically monitoring the Hawai‘i longline fishery for interactions with false killer whales. Fisheries Research, 190, 122–131. https://doi.org/10.1016/j.fishres.2017.02.006.

There are many potential countermeasures to reduce depredation. Passive acoustic recorders, underwater cameras, and accelerometers deployed on long lines are used to monitor activities by toothed whales around longlines. Changes to gear-hauling techniques, such as quicker retrievals and reduced vessel presence, reduce the acoustic cues associated with fishing.

Acoustic “decoy” buoys have been tested to lure whales away from fishing activities^[27]Wild, L., Thode, A., Straley, J., Rhoads, S., Falvey, D., & Liddle, J. (2017). Field trials of an acoustic decoy to attract sperm whales away from commercial longline fishing vessels in western Gulf of Alaska. Fisheries Research, 196, 141–150. https://doi.org/10.1016/j.fishres.2017.08.017. An anchored, underwater buoy emits a sound that mimics the acoustic signature of gear being hauled. Researchers determined that the buoy must be at least 9 km from active fishing activities in order to be effective^[28]Wild, L., Thode, A., Straley, J., Rhoads, S., Falvey, D., & Liddle, J. (2017). Field trials of an acoustic decoy to attract sperm whales away from commercial longline fishing vessels in western Gulf of Alaska. Fisheries Research, 196, 141–150. https://doi.org/10.1016/j.fishres.2017.08.017. Some fishers are concerned that the sounds from decoy buoys may attract more whales to a region, increasing depredation risk. Practical applications of acoustic decoy buoys require more technological research and may only be effective in areas where vessels mainly fish alone, and whales known to interact with longline gear are already present.

Additional Links on DOSITS

• Audio Gallery > Harbor Porpoise
• Audio Gallery > False Killer Whale
• Audio Gallery > Killer Whale
• Audio Gallery > Sperm Whale
• Technology Gallery > Hydrophone/Receiver
• Technology Gallery > Passive Acoustic Recording Tags
• Technology Gallery > Real-time Passive Acoustic Sensors
• Hot Topic > Passive Acoustic Monitoring Critical to Vaquita Conservation Efforts

Additional Links on DOSITS

• Fader, J. E., Elliott, B. W., & Read, A. J. (2021). The Challenges of Managing Depredation and Bycatch of Toothed Whales in Pelagic Longline Fisheries: Two U.S. Case Studies. Frontiers in Marine Science, 8, 618031. https://doi.org/10.3389/fmars.2021.618031.
• Findlay, C. R., Ripple, H. D., Coomber, F., Froud, K., Harries, O., Van Geel, N. C. F., Calderan, S. V., Benjamins, S., Risch, D., & Wilson, B. (2018). Mapping widespread and increasing underwater noise pollution from acoustic deterrent devices. Marine Pollution Bulletin, 135, 1042–1050. https://doi.org/10.1016/j.marpolbul.2018.08.042.
• Gilman, E., Brothers, N., McPherson, G., & Dalzell, P. (2007). A review of cetacean interactions with longline gear. Journal of Cetacean Research and Management, 8(2), 215–223.
• Johnston, D. W. (2002). The effect of acoustic harassment devices on harbour porpoises (Phocoena phocoena) in the Bay of Fundy, Canada. Biological Conservation, 108(1), 113–118. https://doi.org/10.1016/S0006-3207(02)00099-X.
• Kemper, C. M., Pemberton, D., Cawthorn, M., Heinrich, S., Mann, J., Würsig, B., … Gales, R. (2003). Aquaculture and marine mammals: co-existence or conflict? In N. Gales, M. Hindell, & R. Kirkwood (Eds.), Marine mammals: Fisheries, tourism, and management issues (pp. 208–225). CSIRO Publishing.
• Nash, C. E., Iwamoto, R. N., & Mahnken, C. V. . (2000). Aquaculture risk management and marine mammal interactions in the Pacific Northwest. Aquaculture, 183(3–4), 307–323. https://doi.org/10.1016/S0044-8486(99)00300-2
• Quick, N. J., Middlemas, S. J., & Armstrong, J. D. (2004). A survey of antipredator controls at marine salmon farms in Scotland. Aquaculture, 230(1–4), 169–180. https://doi.org/10.1016/S0044-8486(03)00428-9
• Read, A. J., Drinker, P., & Northridge, S. (2006). Bycatch of marine mammals in U.S. and global fisheries: Bycatch of marine mammals. Conservation Biology, 20(1), 163–169. https://doi.org/10.1111/j.1523-1739.2006.00338.x
• Read, A. J. (2008). The looming crisis: interactions between marine mammals and fisheries. Journal of Mammalogy, 89(3), 541–548. https://doi.org/10.1644/07-MAMM-S-315R1.1
• Sepulveda, M., & Oliva, D. (2005). Interactions between South American sea lions Otaria flavescens (Shaw) and salmon farms in southern Chile. Aquaculture Research, 36(11), 1062–1068. https://doi.org/10.1111/j.1365-2109.2005.01320.x
• Tixier, P., Lea, M., Hindell, M. A., Welsford, D., Mazé, C., Gourguet, S., & Arnould, J. P. Y. (2021). When large marine predators feed on fisheries catches: Global patterns of the depredation conflict and directions for coexistence. Fish and Fisheries, 22(1), 31–53. https://doi.org/10.1111/faf.12504.
• Würsig, B., & Gailey, G. A. (2002). Marine mammals and aquaculture: conflicts and potential resolutions. In R. R. Stickney & J. P. McVey (Eds.), Responsible marine aquaculture (pp. 45–59). Wallingford: CABI. https://doi.org/10.1079/9780851996042.0045