TECHNICAL NOTE The Once and Future Ping ...

'TECHNICAL NOTE

The Once and Future Ping: Challenges for the Use of Acoustic Deterrents in Fisheries

Scoff 0. Kraus Edgerton Research Laboratoly New ~nglandAquarium Central Wharf Boston, MA

THE DEVELOPMENT OF ACOUSTIC METHODS TO REDUCE FISHERY/MARINE MAMMAL CONFLICTS

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n the last forty years, with the widespread development of gillnet and driftnet fisheries around the the world, there has been an increase in the rate of incidental catch of marine mammals (Perrin et al., 1994). In the late 1970's, fishermen and aquaculturists in the Pacific Northwest became concerned because of the damage to salmon inflicted by seals. Experimental work was undertaken to solve the problem of pinniped depredation on caught fish, and acoustic deterrents figured prominently in that work (Mate and Harvey, 1986). Researchers used sounds they believed to be annoying or frightening underwater to scare the seals away from the nets. However, the early studies suggested that these acoustic deterrents became less effective over time, and may have subsequently increased the problem by alerting the seals to the presence of caught fish, creating a "dinnerbell" effect (Mate and Harvey, 1986). These studies also provided early evidence for habituation by the wild animals, and indicated that acoustic applications were inconsistent in deterring marine mammaVfishery interactions. Nevertheless, in the 1980's as the developing aquaculture industry continued experiencing conflicts with seals, the use of acoustic deterrents became more widespread. Manufacturers increased the amplitude of the sounds to levels that appeared to be more effective in deterring seals attempting to get into the aquaculture pens. This was possible only because the fixed locations and well-buoyed platforms allowed for the larger transducers and power sources required for loud sound production. These units, called Acoustic Harassment Devices (AHD's), have had to become increasingly loud over the last ten years to remain effective. Current AHD sound source levels range between 194 and 200 db re 1 rnicropascal @ 1 meter, with fundamental frequencies between 10 to 25 kHz (Johnston and Woodley, 1998). There is evidence that such sounds can exclude cetaceans as well as pinnipeds from areas (Olesiuk et al., 1996). Simultaneously in Newfoundland, Canada, cod traps (large boxes of mesh netting designed to catch cod in near-shore waters) were catching increasing numbers of humpback

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whales. A whale rescue team from Memorial University in St. Johns responded to the entanglements of over 500 humpbacks between 1980 and 1990, and the losses to fisherman in damaged gear and lost fishing time were extensive (Lien, 1994). Dr. Jon Lien of Memorial Universily developed several acoustic devices, in an attempt to keep whales out of fishermen's nets. After some success, he switched to a low power electronic acoustic unit (4 kHz fundamental, with source level of 135 db @ 1 micropascal re 1 m) that was portable and reliable. Trials on cod traps in the Newfoundland fishery showed a significant reduction in whaldtrap collisions using these devices (Lien, et al 1992).

THE PORPOISE PROBLEM IN NEW ENGLAND

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n the early 1990's, evidence was mounting that the New England groundfih gillnet fishery was incidentally killing about 2000 harbor porpoise per year. Because of widespread skepticism about acoustic deterrents in the United States (based on the pinniped work in the Pacific Northwest), no government body or private scientists were willing to advocate acoustic solutions to the bycatch problem. A group of fishermen from New Hampshire, under the threat of an endangered species listingfor harbor porpoise, asked Dr. Lien to assess whether his "whale scaring device" might work in the groundfish gillnet fishery. In two years of preliminary trials (1992, 1993) there was strong evidence that these acoustic devices could reduce the incidental take of harbor porpoise, but operational and statistical problem left the results open to debate. An international panel of scientists was convened by the U.S. National Marine Fisheries Service (NMFS) to review all of the work on acoustic deterrents relative to harbor porpoise, and they concluded that a full scale trial with a rigorous statistical design was needed. A large-scale double-blind experiment was conducted off the coast of New Hampshire in the autumn of 1994 within an operational groundfish gillnet fishery. Acoustic deterrent devices (ADD'S, referred to henceforward as "pingers"), producing a 300 rnsec pulse every 4 seconds with a fundamental frequency of 10% (132db re 1 rnicropascal @ 1 m) were spaced every 95 meters along gillnet strings fished in an experimental fishery by 15 participating fishermen. The results indicated that

"pingered" nets reduced harbor porpoise bycatches by an order of magnitude over "un-pingered" nets (Kraus et al., 1997). At this time in the northeastern United States, pingers have been implemented as a management tool for keeping harbor porpoise catches below the level mandated by the NMFS stock assessment group under the U.S. Marine Mammal Protection Act, currently at a level of 483. Although the ability of pingers to help New England gillnetters reach this level is still open to question, it appears that pingers are at least one of the tools which can help f ~ h e r i e sreduce the bycatch of harbor porpoise.

PINGER USE AND QUESTIONS: HOW DO THEY WORK?

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ingers are currently being employed and tested in a variety of fisheries on a number of different cetacean species throughout the world. Tests in the California driftnet fishery showed a dramatic decrease in multi-species bycatch of both cetaceans and pinnipeds when pingers were deployed (Barlow and Cameron, in press), causing NMFS to mandate pingers in that fishery starting in 1998. Other experiments on harbor porpoise in Washington State (Gearin et al., 1996) and in the Danish North Sea gillnet fishery (Larsen, in press) have showed comparable reductions in bycatch rates. However, experiments conducted in South Africa by Vic Peddemors and his colleagues on pinger effects on wild hump-backed dolphins have shown little effect. Work on hectors dolphins in New Zealand by Greg Stone and his colleagues has shown dramatic responses to some pingers, but not others (Stone, et al., 1997). In most other regions where pingers are being tested in fishery trials, rigorous experimental protocols required to answer questions of effectiveness are rarely in place. Unfortunately, we still do not know why pingers work at keeping animals away from nets; every fishery is different, and every dolphin and porpoise species has different hearing and sound production abilities. Also, the social behavior of a dolphin species may have a lot to do with an animal's response to the sounds produced by pingers. In all, the use of ADD'S to reduce bycatch in cetaceans is a pandora's box of anecdotes, gaps in information, and hope from a few successful experiments. In this light, questions about the widespread utility of pingers to solve many cetacean bycatch issues have been raised (Dawson et al, 1998). Central to the question of pinger effectiveness is understanding how and why they work. There are a number of hypotheses that have been put forward to explain pinger effects

on animals. These are summarized below, with a synopsis of the implications of each. -The startle hypothesis states that porpoises are startled and flee when hearing the sound of apinger, a response which is likely to diminish if animals are repeatedly exposed and become habituated to the sound. This could mean that pingers would only be effective until the animals stopped being startled or scared, at which point they would no longer avoid nets. -The alerting hypothesis states that when porpoises hear the sounds, they interogate their surroundings (probably using echolocation), detect the net, and therefore avoid it. An analogy is the yellow line in the center of a highway to keep opposing traffic from colliding. This means that to be effective, pingers must produce sounds that catch the attention of the animals, which means we need to know more about the hearing of many species for which acoustic studies have been limited. -The "annoying" hypothesis is simply that dolphins avoid pingers the way humans avoid static or unpleasant noise. Given the high tolerance of urban humans for trmc and construction noise, it is likely that if pingers are annoying, there is a good argument for believing they will lose their effectiveness over time as animals become habituated to the sounds. -Another suggestion is that the pingers are jamming the animals' sonar. Since the current production pingers have high frequency harmonics, it is possible that a broad-band sound occupying the sonar frequencies of the a target species might drown out sonar clicks, and effectively render the animals acoustically blind. In an oceanic environment with poor visibility, we suspect dolphins would avoid such a signal, although pinger harmonics and ping intervals used to date are not likely to have the power or bandwidth to effectively mask sonar clicks. The great danger of this sort of effect is that if pingers went into widespread use, and pingers did mask sonar signals, large areas of the ocean could be rendered unusable for cetaceans that relied upon sonar for food-finding. -Porpoise or dolphin bycatches may be reduced because pingers cause avoidance by prey species. The 1994 experiment suggested that pingers reduced herring catches, although no other fish were affected. Because herring is a primary food for harbor porpoise, researchers worried that the reduced porpoise bycatch was due to the pinger effect on herring, and not necessarily on porpoise. In another experiment conducted in the spring of 1997, when herring are rare in the New Hampshire fishery, porpoise bycatch reduction was comparable, suggesting that pingers MTS Journal

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work on harbor porpoise independent of prey effects (Kraus and Brault, in press). However, this is a cautionary tale for other fisheries, as this effect could confound the results of pinger experiments on different dolphin species and their prey.

ENVIRONMENTAL AND BEHAVIORAL CONCERNS

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f fishermen put pingers into widespread use, will high-density fishing areas create exclusionary zones for dolphins and porpoises? This would be unacceptable if it forced cetaceans to utilize sub-optimal habitat, as that might lead to population declines. In the Kraus et al (1997) experiment, porpoise were caught in non-pingered nets placed next to pingered nets, suggesting that at least in that study, no exclusion was taking place. However, if pingers are used on every gillnet in a fishery, the situation may be different, and is worth study. Concerns about habituation remain significant. If pingers startle or annoy dolphins, then repeated exposure to the sounds with no adverse consequences will lead to habituation, and pingers may eventually become ineffective. Andy Read and his colleagues have started testing this by exposing wild animals to pinger sounds for extended periods, and monitoring behavioral changes. In a fishery, habituation to pingers will lead to increases in incidental catch rates over time. Habituation may also be a function of the target species social structure-porpoise are known to be solitary and skittish, some dolphins display curiousity and boldness in groups-pingers may work differently in each context. Will pingers become seal attractors? Earlier work in the Pacific indicated that seals used pingers as a way to find caught fish (Mate and Harvey, 1986). In the Kraus et al (1997) experiment, there was no significant difference in seal damage to gillnetted fish between the control and the pinger nets. However, the experiment was only two months long, and anecdotal reports from the Pacific Northwest suggested that pinnipeds there learned to use pingers to find caught fish over a six month to a year-long period. One solution to this problem, if it occurs, is to raise the pinger frequencies above seal hearing, circa 40 kHz. Will pingers affect other non-targeted species, including other protected species and, or commercial fish? To date, there is good evidence high-frequency pingers affect the behavior of herring. Pingers do not appear to affect any other fish group, but there is concern that pingers may affect whales, although information on whale hearing is perhaps less complete than .92

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many of the dolphins. Neverthless, pinger effects on protected cetaceans need to be evaluated.

IS THERE A PERFECT PINGER?

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ishermen have repeatedly asked if it is possible to design an optimal pinger. It may be, but before it can be done, the questions raised above need attention. One way to reduce the probability of habitat exclusion is to develop pingers that are just loud enough for the job. Reducing the range of audibility by making quieter pingers will be a trade off between the range of detection vs the swimming speed of the animal you are trying to keep out of nets. Dolphins must be able to hear the pinger while swimming at full speed and then be able to respond appropriately. This also means the interval between the pings must be kept short enough so that animals are not traveling toward the net for an extended time without a warning. In the New Hampshire experiments, pingers were designed to produce pings just 15dB above ambient noise levels at the fundamental frequency. This meant that at lOkHz, the pingers became inaudible at about 300 m, hardly an ensonification of the ocean. Higher frequencies attenuate even more quickly, and ambient noise levels drop off as frequency increases, suggesting that higher frequency pingers could be effective at quieter sound source levels, and would therefore have a smaller environmental impact. Higher frequencies will also be out of the hearing range of most seals, whales, and fish, reducing concerns on non-target species, and potentially eliminating the "dinnerbell" effect. Another option worth exploring is randomizing the pinger signal. Dave Goodson and his colleagues have been experimenting with this concept in England. Randomizing the period and interval of the signal may reduce the possibility of habituation in dolphins, since pingers along a net would be triggered unpredictably. A randomization of the signal itself may already be occurring within existing commercial pingers, because of inter-pinger variability in the frequency and harmonic characteristics, apparently due to the manufacturing process. Fishing operations are in some ways the ultimate test of electronic equipment. Not only must pingers withstand severe physical abuse on deck, they must perform 24 hours a day while submerged, under pressure, and in cold temperatures. Further, current battery life is only about 30 days on American commercial pingers. Another pinger we tested had an estimated battery life of six months, but did not proven operationally rugged enough for commercial fisheries. Pingers need to have longer battery life than current models, since no fisher-

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man wants to be changing batteries at sea in mid-winter on a heaving spray soaked deck. One possible solution is to use more efficient transducers, with fewer harmonics, requiring less power. Pingers with higher frequencies would also need less battery power, or alternatively, larger pingers that could accommodate more batteries could be developed. Clearly, pinger technology still has a long way to go. The ideal pinger would be acijustable to frequency, harmonics, and sound source level, would be rugged enough for operational conditions at sea with very low failure rates, and operate for at least six months on one battery change. Developing pingers with higher frequencies appears to be a direction worth pursuing. Pingers appear to be effective at reducing the incidental bycatch of harbor porpoise and some other whales and dolphins, but in many fisheries and for most cetacean species, acoustic deterrents remain untested. Because of this,rigorous experimental work on their effectiveness in the particular fishery and on a particular cetacean species should be done before pingers are implemented in a fishery. The utility of using pingers to reduce dolphin bycatch should also be considered in a cultural contextin some subsistence fisheries, they are neither affordable nor maintainable. Still, despite the outstanding questions outlined above, pingers are nevertheless showing promise as a potentially powerful method of reducing one of the maor problems affecting net fisheries and small cetaceans around the world.

REFERENCES CITED Barlow, J. and G.A. Cameron. 1999. Field experiments show that acoustic pingers reduce marine mammal bycatch in the California m e t fishery. Doc. SCI 51iSM2 Draft manuscript submitted to the Scientific Committee of the International Whaling Commission, Grenada, May, 1999. Dawson, S.M., A. Read, and E. Slooten. 1998. Pingers, porpoises and power: Uncertainties with using pingers to reduce bycatch of small cetaceans. Biol. Conservation M141-146.

Gearin, P.J., M.E. Gosho, L. Cooke, R. DeLong, J. Laake, and D. Greene. 1996. Acoustic alarm experiment in the 1995 northern Washington marine setnet fishery. Report of the Nat. Marine Mammal Laboratory, NMFWNOAA and the Makah tribal fisheries management division. 16p. Johnston, D.W. and T.H. Woodley. 1998. A survey of acoustic harrassment device (AHD) use in the Bay of Fundy, N.B., Canada. Aquatic Mammals 24(1):51-61. Kraus, S.D., A. Read, E. Anderson, K. Baldwin, A, Solow, T. Spradlin, and J. Williamson. 1997. Acoustic alarms reduce porpoise mortality. Nature 388: 525. Kraus, S.D. and S. Brault. In Press. A springtime field test of the use of pingers to reduce incidental mortality of harbor porpoises in gill nets. Rep. Int. Whal. Commn. Larson, F. 1999. The effect of acoustic alarms on the bycatch of harbor porpoises in the Danish North Sea gillnet fLshery. Doc SCl51lSM41 Draft manuscript submitted to the Scientific Committee of the International Whaling Commission, Grenada, May, 1999. Lien, J. W. Barney, S. Todd, R. Seton, and J. Guzwell. 1992. Effects of adding sound to cod traps on the probability of collisions by humpback whales. In: Thomas, J. et al. (eds). Marine Mammal Sensory S y s tems. Plenum Press, New York. Lien, J. 1994. Entrapments of large cetaceans in passive inshore f ~ h i n ggear in Newfoundland and Labrador (1979-1990). Rep. Int. Whal. Commn. (Special Issue 15): 149-157. Mate B.R. and J.T. Harvey. 1986. Acoustical deterrents in marine mammal conflicts with fisheries. Oregon Sea Grant Report ORESU-W-88001. 116 p. Perrin, W.F., G.P. Donovan, and J. Barlow. 1994. Report of the workshop on mortality of cetaceans in passive fishing nets and traps. Rep. Int. Whal. Commn. (Special Issue 15):6-57. Olesiuk, P.F., L.M. Nichol, P.J. Sowden, and J.K.B. Ford. Effect of sounds generated by an acoustic deterrent device on the abundance and distribution of harbour porpoise (Phocoaa phocoaa) in Retreat Passage, British Columbia. Draft Report for the Canadian Dept. of Fisheries and Oceans, Pacific Biological Station, Nanaimo, B.C. 47 p. Stone, G., S. Kraus, A. Hutt, S. Martin, A. Yoshinaga, and L. Joy. 1997. Reducing bycatch: can acoustic pingers keep Hector's dolphins out of fishing nets? Marine Technology Society Journal 31(2):3-7.

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