Theme Session (C) By-catch of mGoodson et al. "Aversive sounds an

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Aversive soun~s and sound pressure levels rar the harbour porpoise(PluJcoella pllOcoella): an initial field study.

Goodson AD., Amundin M., Mayo R.H., Newborough D., Lepper P.A. Loekyer, C., LarsenF. & Blomqvist C.

·AßSTRACTHarbour porpoise foraging behaviour "ithin a sea loeh was studied by traeking surfacing positions witheleetronie theodolites. A regular pattern was noted whieh brought a few animals to forage eaeh day \\ithin asrnaliland loeked bay. This area was selected to evaluate the eIreet of prototype wide band acoustic devieesintended as gillnet cetacean bycatch deterrents. Two harbour porpoises werc tracked entering the bay andfollowOO for some 30 minutes while apparently foraging in a 25 m depth depression in the seabed. During thisperiod canoes were positioncd across tbe entrancc to the bay and three acoUstic dC\ices were activated fromtbese when the 1\\'0 porpoises slowly started to head out from tbc bay. Tbc sound sources were activated whentbc lead animal approaebed \\ithin 100 m of a canoe. A distinct change in the s\\imming direction andsulfacing beha\iour was noted after activation. Botb animals reversing tbdr s\\imming direetion and theytravelled rapidly at 2 ms'\ towards tbc sbore line, surfaced once at the 10 m contour, and continued towards thefar end of the bay. Tbe porpoises tben maintained a minimum separation from tbc sound sourees of 640 m.The sound signals \vere deaetivated after 30 minutes and the two animals tben promptly beaded back towardsthe entrance to the bay. Re-activation ofthe sound sources for tbc second time occurred after a small delay, asthe porpoises were sighted close to the eanoes. On this oceasion the lead animal crossed tbc line of tbc devicesbefore, or as, these \vere activated and continued into the main sea loch. The second porpoise again reversed itss\\imming direction and returned back into the bay. Increasing "ind and surface rougIuiess made the canoeplacements difficult to maintain and as sigbting conditions deteriorated tbc test was discontinued. The areawas monitored during tbe follO\\ing morning in 11at calm conditions and porpoises were again observedentering and foraging in the same area. Tbc experimental acoustie devices emitted low level signals based onearlier work wbich had indicated that \\idcband sounds at quite high frequencies were apparently aversive atlow Sound Pressure Levels to harbour porpoiscs. The signals prcscntcd in this sca loch test alternated at 4sccond intervals betwecn two different frcqucncy modulated signals, swept \\itbin a band between 20 kHz and160 kHz. Tbc experimental devices peak Source Le"el was measured to be 152 dB re Ippa at Im. The SPL at640 m was estimated to be in the order of 88 to 95 dB re IJ.lPa and this may thcrcfore indicate an 'aversive'sound prtessure level threshold to these particular signals from whieh acoustie parameters affeeting devicedeployment spacing along a fishing net ete. may be eonsidered.

Kcy "'ords : aeoustie, behaviour, bycatch, cetaeean, gillnets, harbour pofpoise, pingcr.

Correspondence to: A D Goodson, Underwater Acoustic Group, E/ectronic & Electrica/ EngineeringDepartment, Loughborough University. LEI1 3TU, UK.Tel +441509222846, email: a.d.goodson@/boro.ac.uk

IntroductioriThe byeateh of the harbour porpoise Phocoena phococna in bottom-set gillnet fisheries issignifiearit in most Northern hemisphere continental shelf fisheries. The problem appears to begeneral, the. eauses are not fuHy understood and efTeetive solutions elusive. Reeerit studies(Kraus cl al., 1995 and Lien el al., 1995) iridicate that the use of active. sound producingdeVices or pingers ~Ütaehed to such nets ean reduee the number of mortalities and work tomake sueh deviees more emcient is in progress (Newborough. ct al, 1997). The firstgeneration of sound producing devices applied to bottom set gillnets were derived from lowfrequency whale alarms optimised for maximum efTeet on bil.1een whales ofT the Newfoundlandcoast. These deviees were intended to be made cheaply by fishermen from easily availablecomponerits and although effeetive in their iritended applieation their electro-acousticemcieney is low. A test of two of such devices earried out using rehabilitaied, ex-stranded,juvenile porpoises demonstrated that the 2.5 kHz fundamental of these alarms was pitched at

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Theme Session (0) By-catch ormarine mammals: ICES Baltimore September 1997 - File: ices97_1.doc CM 1997/Q: 17Goodson et al. •Aversive sounds and sound pressure levels ror the harbour porpoise Phocoena phocoena: an initial field study.·

too low a frequency to be beneficial although one device, with significant higher hannonicspresent in the signal waveform, produced a strong reaction, (Kastelein cl GI., 1995). Animproved version ofthis analogue technology pinger was deve10ped for the tests carried out irithe Gulf of Maine by Kraus and his colleagues. Their second generation pinger, nowmanufactured commercially, was specified to produce pulsed tonal signals piiched at 10kHzwith a minimum Source Level (SL) of 130 dB re IJ..lPa at 1m. Other recent studies, whilst ingeneral supporting the early findings, have raised the question that the oDserved reduction inbycatch of porpoises might be an indirect efTect, with the preferred prey Hcrring beingdeterred rather than the porpoise. Other concems, includirig the rapid rates" of habitmition tonew stimuli shown by most small cetaceans, were discussed at an NMFSIMMC workshop heldin Seattle (Reeves cl GI. 1996). Some field studies, e.g. Gearin cl GI., 1996) have continued totest using first generation technology low power and low fundamental frequency pingers.Most first generation devices exploit commercially available air matched pieza-tranducers of aHe1mhoItz type resonant in the 2 to 3.5 kHz range (\vith or without some higher harrnonics)and these operate with pulse lengths in the order of 250-400 ms arid with regular inter-pulseperiods usually selected between 1 and 4 seconds. (These sound similar to motor vehic1ereversing hazard beepers). In this underwater appHcation these transducers make inefficient ~-­sound producers as they are not adapted to couple sound into seawater with its very differentacoustic impedance. These devices also seem to have been selected without consideration ofthe harbour porpoise's audiogram, (Andersen, 1970). Such low frequency devices are audibleto some fish species and may only function as deterrents for porpoises when higher harmonicsof the signal are present. However, the actual level of these spectral components variesunpredictably between devices and the SL produced is directly affected by the state of thebattery voItage.

A less empirical approach was sought whilst trying to define suitable signals needed far,ci moreefficient active acoustic deterrent now being developed at Loughborough University. Purposebuilt digital signal synthesis equipment (Woodward & Goodson, 1994) was devised to carryout a number of tests with captive harbour porpoises in which these anirrial's sensitivity andaversion to sounds differing in frequency and in waveform have been examined, (KasteIein clGI., 1997). The resuIts of these tests suggest that higher frequencies appear to be moreaversive than low frequencies and the strongest avoidance reactions obserired were producedby increasing the signal bandwidth. Increasing bandwidth by simply shortcning the pulse eduration to a 'dick' produced Httle obvious effect aIthough it is be1ieved that short bursts ofsuch clicks may stimulate an attentive echolocation response. Increasing the bandwidth byfrequency modulating the signal as a chirp or as a frequency sweep appeared appreciably moreeffective than a single tonal signal pitched within the same band and transmitted for the sameduration. \Videband swept signals also seemed to produce Httle obvious habituation afterrepetitive exposure during a 4 week test period. :

A prototype digital active acoustic deterrent, based on a miero-controller digital synthesiser,was deveIoped which generates two different wide band swept signals. One of these signalssweeps up the frequency spectrum from 20 kHz to 160 kHz the second signal sweeps downand these are emitted at 4 second intervals. A fieId study, tracking and observing wild harbourporpoises within a Scottish sea loch was carried out in September 1996 and the effect of thesencw dctcrrent signals was observed in an interactive test at the end ofthis period.

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Theme Session (0) By-catch of marine mammals: ICES Ba/limore September 1997 - File: ices97 1.doc CM 19971Q: 17Goodson et al. "Aversive sounds and sound pressure levels for the harbour porpoise Phocoena phocoena: an initial field study."

Materials and MethodsThe behaviour of harbour porpoises In a Scottish sea loch was studied using electronictheodolites to track individual animals by their surfacing positions. A short interactiveexperiment was than made to examine the effectiveness of a new acoustic beacon designed tomark fishing nets, (Mayo et al. 1997; Goodson & Newborough, 1997). The active digitalsound sources were packaged in small waterproof plastic containers with a water sensingswitch and these were moored below surface floats on approximately 3 m of line. The surfacetloat was then attached to a longer line to allow these to be streamed behind the canoe orsimply deployed over the side when required. An additional study tool was provided by a lowpower radio telemetry sonobuoy equipped with a 'elick detector' circuit designed to envelopedetect the high frequency echolocation pulses from the porpoises and make these audible andrecordable with audio bandwidth equipment. The receiving equipment for these radio signalswas coupled to the sound track of a fixed position video camera which was set up to recordactivity elose to the entrance to the bay.

Pre-TestRegular foraging behaviour was observed in an enelosed area of the loch with a narrowentrance 400 m wide. In very calm conditions, two porpoises were carefully tracked enteringthis area and were then observed to forage far aperiod of 30 minutes. Two canoes werepositioned across the bay entrance during this period and a radio telemetry sonobuoy waslaunched to drift in the same vicinity. The canoes were in VHF radio communication with twotheodolite survey positions and with a video camera operator based on the headland elosest tothe entrance. The canoes then remained in position ready to deploy three acoustic devicesacross this constricted entrance to the bay.

TestThe porpoises, still apparently foraging, moved towards the entrance and the first beacondevice was activated 100 m from the nearest animal at 13.09, the second almostsimu1taneously and a 3rd within approximately 2 rninutes as the deploying canoe towing thefirst device moved quietly to a new position some 50 m away this manoeuvre left the threepingers spread out in a line across the deeper water at the entrance to the bay.The animals were not observed for the next 171 seconds, after which they surfaced 340 maway (a sustained swimming speed of 2 m/s). For the next 30 rninutes, while these devicesremained active, very few surfacings were observed and all of these were grouped as far fromthe beacons as possible usually at the edge ofthe area's deep water (lOm contour).

. Post-Test ~

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Pre-Test 0d6"-.J;:/'

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Figure 1. Surfacing positions obtained by theodolite while tracking 2 harbour porpoises before, during andafter the acoustic deterrent signals were presented. = marks the positions of the sound sources deployed bycanoes. T = theodolite position on hi/lside.

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Theme Session (C) By-catch of marine mammals: ICES Baltimore September 1997 - File: ices97_1.doc· CM 1997/Q: 17Goodson et al. "Aversive sounds and sound pressure levels for the harbour porpoise Phocoena phocoena: an initial field study."

Note - although most ofthe porpoise sufacings in this area were actually seem by the team ofobservers, some ofthe theodolite plotted positions were missed as the surfacing behaviour hadchanged to a very rapid single breath taken at rather longer intervals. This changed behaviourmade the theodolite tracking operation more difficult.

Post-TestThe pingers were withdrawn at 13.38 and the next surfacings observed after this were 120 meloser towards the entrance. At 13 .51 both animals were observed at the entrance and theacoustic devices were re-activated. One animal tumed back and the other left the area.Viewing conditions during the succecding half hour detcrioratcd as a light ,virid sprarig up andthe rippled surface made theodolite sighting impossible. The experiment was terminated at14.12. The radio telemetry buoys were recovered, unfortunately these had drifted off stationduring the test and provided no useful data on this occasion. The following morning underexcellent vie\ving conditions several animals were observed foraging in the area of theexperiment.

Results and DiscussionThis first field test employed signal sources with a peak SL only a little louder than the devicesused in the Gulf ofMaine, it is worth noting that the devices operate from a regulated powersupply and, unlike earlier analogue designs, do not suffer a progressive reduction in SL withfalling battery voltage. In any future test a seabed mounted hydrophone cabled to the shoremay provide useful measurements of the actual sound pressures, background noise levels andmay detect the presence, or cessation, of echolocation behaviour when the acoustic stirimli areactivated. Similarly, introducing remote control of the sound sources which can be pre­postioned on individually moorings would be advantageous.

The aversive effect observed in this test seemed pronounced and the porpoises were promptlydisplaced more than 640 m away from these sound sources, (figure 1). Propagation coriditionsin this bay suggest that at this distance the porpoises wcre reacting to sound pressures whichhad been reduced by spreading and absorption loss to around 88 to 95 dB re 1 JlPa. Inter­device spacings along a gillnet rnight therefore be increased above the 50 m maximum iritervalsemployed in earlier field tests with some confidence. These new signals appear aversive to theharbour porpoise at very low sound pressure levels.

The deployment of such acoustic deterrents in a commercial fishery must also take intoaccount the net's geometry and the device's proximity to the seabed. Headrope mounting willbe normally be preferred to lift the sound source above the seabed and thus improve theeffective range. For 'tangle nets' or other gillnet configurations where the headrope may lie onor elose to the seabed a eloser inter-device spacing interval should be considered. Suchspacings need to be selected for each type of net but even when these are deployed on theseabed their predicted zones of influence should overlap to accommodate apossible singledevice failure. These studies have focused on the development of more' efficient activeacoustic mitigation devices. The work described refers to development work on technicallyimproved devices to deter harbour porpoises. These are intended to be applied as bycatchmitigation measures for bottom-set or sink gillnets where these nets are known to have asignificant incidental catch ofharbour porpoises.

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Theme Session (Q) By-catch of marine mammals: ICES Baltimore September 1997 • File: ices97_1.doc CM 1997/0: 17Goodson et at. "Aversive sounds and sound pressure levels for the harbour porpoise Phocoena phocoena: an initial field study."

AcknowledgementsThis work was supported by the UK Ministry of Agriculture Fisheries and Food~ the UKDepartment of the Environment~ the European Commission DGXIV and the Danish Institutefor Fisheries Research. The logistic assistance provided during the preparation of these testsby Mr P.Copland (Scottish Office Marine Laboratory) is greatfully acknowledged.

ReferencesAndersen S. (1970) Auditor)' sensitivity of the harbour porpoise Phocoena phocoena. In: Investigations onCetacea Vol II Ed: G.Pilleri. Institute for Drain Research, Dem, 255-259.Gearin P.I, Merrill E., Gosho M.E., Cooke L., DeLong R, Laake J. and Greene D. (1996). Acoustic alarmexperiment in the 1995 Northem Washington Marine Setnet Fishery. Report prepared by US Department ofCommerce, National Oceanic and Atmospheric Administration, National Marine Fisheries Service, NationalMarine Mammal Laboratory and Makah Tribai Fisheries Management Dhision. (March 1996). p16.Kraus S., Read A, Anderson E., Bald"in K., Solow., Spradlin T. and Williamson J. (1995)A field test ofthe use ofacoustic alarms to reduce incidenta1 mortality ofHarbor porpoises in gill nets. Reportto NMFS (April 20 1995).Lien I, Hood C., Pittman D., Ruel P., Borggaard D., Chisholm C., Weisner L., Mahon T and Mitchell D.(1995). Field tests of acoustic de\ices on ground fish gillnets: assessment of effectiveness in reducing harbourporpoise by-catch. in: Sensory systems oJaquatic mammals. RAKastelein, IAThomas & P.E.Nachtigall(oos). De Spil, Woerden, NL. ISBN 90-72743-05-9. pp349-364.Kastelein RA Goodson AD. Lien J. and de Haan D. (1995) The effects ofacoustic alarms on harbourporpoise behaviour. in: IIarbour porpoises: laboratory studies to reduce bycatch. P.E. Nachtigall, I Lien,Kastelein RA., de Haan D., Goodson AD. Staal C. and Vaughan N. (1997) The effects ofvarious sounds on aharbour porpoise (Phocoena phocoena). in: The biology oJthe harbour porpoise. AIRead., P.RWeipkema &W.W.L.Au and AJ. Read (eds). De Spil, Woerden, NL. ISBN 90-72743-06-7 pp157-167.Mayo RH., Amundin M., Goodson AD., Lockyer C.H., Lepper P.A., Newborough D., Larsen F. andBlomqvist C. (1997) Observed surfacing behaviour of wild harbour porpoises. In: Research on Cetaceans - 11,Ed: P.Evans, Proceedings ofthe European Cetacean Sodety conference held at Stralsund, Gerrnany, March1997 (in press).Newborough D., Goodson AD. and Woodward B. Set gillnet acoustic deterrents for harbour porpoises,Phocoena phocoena: improving the technology. ICES CM 1997/Q: 16 ([his meeting).Reeves RR, Hofman RI, Silber G.K. and Wilkinson D. Acoustic deterrence of harmful marine mammal­fishery interactions, (1996) ProceOOings ofthe Seattle Workshop held in March 1996. National MarineFisheries ServiceIMarine Mammal Commission, USA.P.E.Nachtigall (eds). De Spil, Woerden, NL. ISDN 90-72743-07-5. pp367-383Woodward, B. and Goodson AD. (December 1994). Prevention ofthe by-catch of cetaceans by exploiting theire acoustic capability). Report for the European Commission DGXIV. Special Study Contract PEMl93/04.

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