PAPER Marine Mammal Behavioral Response Studies in Southern California: Advances in Technology and Experimental Methods AUTHORS Brandon L. Southall Southall Environmental Associates, Inc., Aptos, California Long Marine Laboratory, University of California, Santa Cruz Duke University Marine Laboratory David Moretti Naval Undersea Warfare Center, Newport, Rhode Island Bruce Abraham Applied Physical Sciences Corporation, Groton, Connecticut John Calambokidis Cascadia Research Collective, Olympia, Washington Stacy L. DeRuiter Centre for Research into Ecological and Environmental Modeling, University of St. Andrews Peter L. Tyack Sea Mammal Research Unit, Scottish Oceans Institute, University of St. Andrews ABSTRACT Behavioral response studies (BRS) are increasingly being conducted to better understand basic behavioral patterns in marine animals and how underwater sounds, including from human sources, can affect them. These studies are being enabled and enhanced by advances in both acoustic sensing and transmission tech- nologies. In the design of a 5-year project in southern California (“SOCAL-BRS”), the development of a compact, hand-deployable, ship-powered, 15-element vertical line array sound source enabled a fundamental change in overall project configu- ration from earlier efforts. The reduced size and power requirements of the sound source, which achieved relatively high output levels and directivity characteristics specified in the experimental design, enabled the use of substantially smaller re- search vessels. This size reduction favored a decentralization of field effort, with greater emphasis on mobile small boat operations capable of covering large areas to locate and tag marine mammals. These changes in configuration directly contributed to significant increases in tagging focal animals and conducting sound exposure experiments. During field experiments, received sound levels on tagged animals of several different species were within specified target ranges, demon- strating the efficacy of these new solutions to challenging field research problems. Keywords: marine mammals, noise, underwater sound, transducer, behavioral response study Introduction H ow noise from human activities affects marine life has been an area of increasing investigation and associ- ated technology development (see NRC, 2003, 2005; Southall et al., 2007, 2009). Advanced passive listen- ing capabilities have been used to quantify acute impacts of human sounds (e.g., Clark et al., 2009; McCarthy et al., 2011) and monitor acoustic habitats (see Van Parijs et al., 2009). The development of sophis- ticated tags deployed on animals that record movement and received sounds (see Johnson et al., 2009) has signifi- cantly advanced the ability to measure behavior in marine mammals. There are increasing concerns re- garding chronic noise and marine life (e.g., Clark et al., 2009), but much of the public and regulatory interest in the effects of noise on marine life derived from marine mammal strand- ing events coincident with military active sonar exercises (e.g., Frantzis, 1998; Balcomb & Claridge, 2001; Fernandéz et al., 2005). These events demonstrated that in certain con- ditions, some sounds can harm or mortally injure marine mammals. As reviewed by Cox et al. (2006) and D ’ Amico et al. (2009), there are some similarities among these events. All involved midfrequency active (MFA) military sonar (and in some cases, other active sources) used in deep water fairly near shore. Addition- ally, injured or dead individuals were predominately from a few beaked whale species, and they mass-stranded within hours of nearby naval active sonar exercises. Despite these similari- ties and fairly intensive investigation of 48 Marine Technology Society Journal
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P A P E R
Marine Mammal Behavioral ResponseStudies in Southern California: Advancesin Technology and Experimental MethodsA U T H O R SBrandon L. SouthallSouthall Environmental Associates,Inc., Aptos, California
Long Marine Laboratory, Universityof California, Santa Cruz
Duke University Marine Laboratory
David MorettiNaval Undersea Warfare Center,Newport, Rhode Island
Bruce AbrahamApplied Physical SciencesCorporation, Groton, Connecticut
John CalambokidisCascadia Research Collective,Olympia, Washington
Stacy L. DeRuiterCentre for Research into Ecologicaland Environmental Modeling,University of St. Andrews
Peter L. TyackSea Mammal Research Unit,Scottish Oceans Institute,University of St. Andrews
A B S T R A C TBehavioral response studies (BRS) are increasingly being conducted to better
understand basic behavioral patterns in marine animals and how underwatersounds, including from human sources, can affect them. These studies are beingenabled and enhanced by advances in both acoustic sensing and transmission tech-nologies. In the design of a 5-year project in southern California (“SOCAL-BRS”),the development of a compact, hand-deployable, ship-powered, 15-element verticalline array sound source enabled a fundamental change in overall project configu-ration from earlier efforts. The reduced size and power requirements of the soundsource, which achieved relatively high output levels and directivity characteristicsspecified in the experimental design, enabled the use of substantially smaller re-search vessels. This size reduction favored a decentralization of field effort, withgreater emphasis on mobile small boat operations capable of covering largeareas to locate and tag marine mammals. These changes in configuration directlycontributed to significant increases in tagging focal animals and conducting soundexposure experiments. During field experiments, received sound levels on taggedanimals of several different species were within specified target ranges, demon-strating the efficacy of these new solutions to challenging field research problems.Keywords: marine mammals, noise, underwater sound, transducer, behavioralresponse study
Introduction
How noise from human activitiesaffects marine life has been an areaof increasing investigation and associ-ated technology development (seeNRC, 2003, 2005; Southall et al.,2007, 2009). Advanced passive listen-ing capabilities have been used toquantify acute impacts of humansounds (e.g., Clark et al., 2009;
McCarthy et al., 2011) and monitoracoustic habitats (see Van Parijs et al.,2009). The development of sophis-ticated tags deployed on animals thatrecord movement and received sounds(see Johnson et al., 2009) has signifi-cantly advanced the ability to measurebehavior in marine mammals.
There are increasing concerns re-garding chronic noise and marine life(e.g., Clark et al., 2009), but muchof the public and regulatory interestin the effects of noise on marine lifederived from marine mammal strand-ing events coincident with militaryactive sonar exercises (e.g., Frantzis,1998; Balcomb & Claridge, 2001;
Fernandéz et al., 2005). These eventsdemonstrated that in certain con-ditions, some sounds can harm ormortally injure marine mammals. Asreviewed by Cox et al. (2006) andD ’Amico et al. (2009), there aresome similarities among these events.All involved midfrequency active(MFA) military sonar (and in somecases, other active sources) used indeep water fairly near shore. Addition-ally, injured or dead individuals werepredominately from a few beakedwhale species, and they mass-strandedwithin hours of nearby naval activesonar exercises. Despite these similari-ties and fairly intensive investigation of
48 Marine Technology Society Journal
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14. ABSTRACT Behavioral response studies (BRS) are increasingly being conducted to better understand basic behavioralpatterns in marine animals and how underwater sounds, including from human sources, can affect them.These studies are being enabled and enhanced by advances in both acoustic sensing and transmissiontechnologies. In the design of a 5-year project in southern California (?SOCAL-BRS?) the development ofa compact, hand-deployable, ship-powered, 15-element vertical line array sound source enabled afundamental change in overall project configuration from earlier efforts. The reduced size and powerrequirements of the sound source, which achieved relatively high output levels and directivitycharacteristics specified in the experimental design, enabled the use of substantially smaller researchvessels. This size reduction favored a decentralization of field effort, with greater emphasis on mobile smallboat operations capable of covering large areas to locate and tag marine mammals. These changes inconfiguration directly contributed to significant increases in tagging focal animals and conducting soundexposure experiments. During field experiments, received sound levels on tagged animals of severaldifferent species were within specified target ranges, demonstrating the efficacy of these new solutions tochallenging field research problems.
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damage to stranded marine mammals(e.g., Fernández et al., 2005), the un-derlying direct physical and/or behav-ioral mechanisms for the injuries andmortalities observed remain unknown.
The need for directed behavioralresponse studies (BRS) of marinemammal responses to human sounds,including midfrequency sonar signals,has thus been widely recommended byvarious scientific and government bod-ies (e.g., NRC, 2003; Cox et al., 2006;Southall et al., 2007, 2009; Boyd et al.,2008). The basic methods for con-ducting controlled exposure experi-ments (CEEs) to measure behavioralresponses have been developed in stud-ies on terrestrial animals and applied tothe marine environment (see Tyack,2009).
Recent studies have used thesemethods in studying responses to sim-ulated military sonar. In 2007–2008, aBRS testing the responses of taggedmarine mammals to simulated MFAsonar was conducted at the U.S. Navy’sAtlantic Undersea Test and Evalua-tion Center (AUTEC) in the Bahamas.The responses of Blainville’s beakedwhales (Mesoplodon densirostris), oneof the species involved in previousstranding events following actual mili-tary sonar exercises, included clearchanges in vocal and diving behaviorand sustained avoidance following ex-posure to simulated sonar, predatorsounds, and pseudorandom noise(Tyack et al., 2011); these experimen-tal results were consistent with oppor-tunistic observations of animals inresponse to realistic military exercisesin the same study. This was the firstmeasurement of individual beakedwhales of any species exposed toknown levels of MFA sonar in aCEE; the results are thus extremely im-portant. However, given the relativecost and effort, the total number of
CEEs conducted was quite small.This was due to constraints includingfew suitable weather days; relativelylow animal density, especially beakedwhales at AUTEC with ∼25 animals/1,000 km (Moretti et al., 2006;Marques et al., 2009); and the diffi-culty associated with attaching tags tobeaked whales. A follow-on researcheffort in the western MediterraneanSea in 2009, while managing to surveynumerous poorly known areas andachieve several significant technologi-cal advances, also had limited suc-cess in tagging and conducting CEEs(D’Amico et al., 2010).
A related project, in terms of objec-tives and some aspects of methodology,is the “3S” research collaborationamong academic scientists and DutchandNorwegian Navies. The first phaseof this project (2006–2009) studiedthe behavioral effects of naval sonaron killer whales (Orcinus orca), spermwhales (Physeter macrocephalus), andlong-finned pilot whales (Globicephalamelas) in Norwegian waters; a secondphase is ongoing, focusing on ad-ditional marine mammal species.This project is generally similar to theBahamas BRS projects in terms of theoverall team configuration and experi-mental methodology, in that it usesacoustic tags to measure responses ofanimals to controlled sonar and othersignals. However, 3S has a broader spe-cies focus to provide more operationalflexibility based on optimal animal andweather conditions. Additionally, a re-alistic towed sound source was used,which allowed aspects of relativemovement to be manipulated inorder to mimic aspects of sonar inter-actions with marine mammals. Thefirst phase of the 3S project manageda higher success rate of tagging andCEEs with received sound levels inthe specified target range than in the
Bahamas BRS (for 190 more details,see the 3S phase I final 191 report ath t t p : / / s o i . s t - a n d r ew s . a c . u k /192 documents/424.pdf ), althoughon a variety of species generally easierto tag than beaked whales.
The Bahamas and MediterraneanSea BRS efforts involved large (∼100 m)oceanographic research vessels, largeresearch teams, somewhat limitedmobility and independence of smallvessel operations, and the regimentedtest plans typical of complex field proj-ects. Some of these characteristics(e.g., the need for interdisciplinary ex-pertise within the research team) areunavoidable given the complexity ofacoustical and biological methods andmeasurements. However, other fea-tures resulted from the initial study de-sign. For instance, as in many previousoceanographic acoustic studies involv-ing relatively loud acoustic transmis-sions, quite large underwater soundsources were used to produce the re-quired sound levels. These sourcesweighed hundreds of kilograms and re-quired a room full of amplifiers andcooling equipment. This in turn neces-sitated the use of a large support vesselwith ample deck space and an A-framefor deployment. The consequent useof large, oceanographic research vesselsresulted in relatively high cost and ageneral inflexibility in operationaltimes and areas. With this configura-tion of a large research platform to sup-port large teams and sound sourcerequirements, operations were highlycentralized, with visual detection andmonitoring teams predominatelybased on or near this large, slower ves-sel. The height and stability of the ob-servation platform on these ships hasclear advantages for visually surveyinglarge areas. However, it favored theuse of small boats that could be keptaboard the larger vessels and deployed
July/August 2012 Volume 46 Number 4 49
in ideal conditions to follow and tagnearby animals. Their restricted abilityto search large areas and be immediatelyready to capitalize on any available op-portunities to deploy tags was a keylimiting factor the number of CEEscompleted.
These earlier studies achievedimportant accomplishments and pro-vided valuable data to inform man-agement decisions and operationalplanning for the Navy (e.g., Tyacket al., 2011), despite the limited sam-ple size. In evolving the Bahamas BRSefforts, researchers and program man-agers debated options for modifyingstudy methodologies and technologiesto enable testing more individuals andspecies in a more efficient and eco-nomical manner.
In 2010, the U.S. Navy began sup-porting a multiyear interdisciplinarybehavioral research effort in southernCalifornia (“SOCAL BRS”). The in-tent was to build on the accomplish-ments of earlier studies while derivinga more agile, cost-effective study thatincreased the number of species andindividuals tested. An experimentaldesign similar to previous research ef-forts was used, involving a scaledsound source projecting simulatedmilitary sonar signals and acoustic/movement tags on animals to measurecalibrated received sound levels andbehavioral responses. Utilizing this de-sign, the overall approach in the firstyear of this study (SOCAL-10) wasto: (1) concentrate efforts in an areaof relatively higher marine mammaldensity and species diversity to enableflexibility in species selection based onconditions; (2) emphasize flexibility bystreamlining the size, complexity, andrigid scheduling of previous operationalplans, with the development of a smal-ler sound source being a key enabler;and (3) decentralize the nature of the
research teamwith an emphasis onmo-bility and capability of small boat op-erations. This paper focuses on themodifications in experimental designand sound source technology used inSOCAL-10 and refinements based onlessons-learned in SOCAL-11.
Experimental MethodsThe primary objective in modify-
ing configurations from earlier studieswas increasing efficiency and opera-tional mobility for rapid response toareas of favorable weather and availablesubjects. A significant challenge was inreducing the size of the primary re-search vessel for conducting CEEs. Adriving factor in the previous use oflarge vessels was the requirement forlarge underwater sound projectors togenerate sufficiently loud signals.While using source levels well belowthose of actual military midfrequencysonar systems (∼235 dB RMS [rootmean square] re: 1 μPa [hereafter dB]at 1 m), this and previous studies pro-jected midfrequency (3–4 kHz funda-mental frequency) sonar signals thatsimulate military systems in certain re-gards (stimulus waveform, duration,and duty cycle) at source output levelsof up to ∼210 dB.
The ability to project simulatedmidfrequency sonar signals at such lev-els from a system that was hand-deployed, powered, and operatedfrom a much smaller research vesselwas a significant technical challenge.To streamline the SOCAL-BRS in re-lation to previous projects, engineersworking in collaboration with biolo-gists undertook the design of such asystem. Achieving this objective provedcritical in modifying the experimentaldesign to enable amoreflexible researchconfiguration with CEEs on a relativelylarge number of species and individuals.
Sound Source Developmentand Testing
The CEE protocols called for pro-jecting relatively short (∼1.5 s) simu-lated midfrequency sonar sounds andpseudorandom noise signals with pre-dominant energy in the 3-4 kHz bandonce every 25 s for up to 30 min. Thetarget for received sound levels on focalanimals during CEEs was ∼100-160 dB.Accounting for propagation lossesfrom a source ∼1 km from the animals(the notional range during transmis-sions), this meant that source levelsfor these midfrequency sounds hadto be capable of generating ∼160 to∼210 dB at 1 m. The nontrivial engi-neering objective was to develop, cali-brate, and operate a sound source thatcould achieve these output specifica-tions in an overall package that couldbe housed, powered, rapidly hand-deployed (<5 min) to 30-m depth,and recovered from a medium-sized(15–30 m) research vessel. In designingthis source, it was assumed that, as inprevious studies, the exposure levelwould be directly measured using a cal-ibrated animal-borne tag. This assump-tion relaxed the requirement for anomnidirectional source and made possi-ble the use of a lightweight array with amore complex beam pattern.
A vertical line array (VLA) of activetransducers was selected as the sourceconfiguration for projecting mid-frequency, short-duration sounds.This VLA consisted of 15 individualtransducer elements with a 15.2-cm(6-inch) center-to-center spacing,each driven by individual 800-Wclass D power amplifiers throughstep-up transformers and tuning induc-tors. The transducers (GeospectrumTechnologies, Ltd., model #M21-3750) were of an air-backed, flexuraldisk design. Each transducer had twolead zirconate titanate (PZT) disks
50 Marine Technology Society Journal
bonded to metal disks, which were inturn bonded to a housing to form aclosed air cavity. The transducerswere each encapsulated in urethaneto provide waterproofing and somemechanical damping. Their electro-acoustic efficiency was approximately86% at 3.8 kHz, which is the centerfrequency of both signals used in theSOCAL-BRS. The array structurewas designed to be relatively light-weight and flexible to allow for handdeployment. Each transducer sat in aPVC “holder” through which fourflexible wire ropes passed. The wireropes supported the transducers andset the element spacing. The trans-ducer holders were held in place withcrimped-on locking collars.
The VLA was suspended from analuminum pressure housing (Prevco,Inc.) on four stainless steel cables andpowered through a 125-m Kevlarreinforced (1000-V-rated) electro-mechanical cable (Figure 1). Individualtransducers were connected to tuninginductors mounted inside the pressurehousing. The 38-mH inductors werewired in series with each transducerto minimize the volt-amps requiredfrom the amplifiers and also increase
the bandwidth of the system. Dryweight of the entire VLA was ∼40 kg,including a small ballast weight at-tached to ensure the array hung verti-cally. A roll/pitch/depth sensor withRS-232 output was mounted insidethe pressure vessel to measure the ori-entation of the source array in thewater column. A vertical displacementangle of less than 5° was typicallymaintained during field operations,which typically occurred in sea statesof Beaufort 3 or less (4 max). Thetotal overall deployed dry weight ofarray, ballast, and cable was <50 kg(wet weight < 10 kg), enabling easy,safe, and rapid hand deployment bytwo or three people.
The dry-end of the system con-sisted of three amplifier banks, eachcontaining five independent modules.The 800 W, Class D audio amplifierswere built by Harrison Labs and have arated efficiency of 88% at full power.The amplifiers were powered by 12 Vsealed lead acid batteries (one per am-plifier). A custom Edcor USA step-uptransformer increased the voltageout of the amplifier by a factor of5.7 times. The batteries were rechargedbetween each signal transmission
using simple sealed lead acid (SLA)chargers powered by 120 VAC, 10 Aship power. All components wereshock-mounted in a rugged, shipping-ready rack (45 × 74 cm) readily loadedand housed on small research vessels.A 1U (1 unit standard-size) rack-mountsource control computer with a Na-tional Instruments multichannel digital-to-analog (D/A) PCI (NI PCI-6723)card generated the audio signals driv-ing the audio amplifiers.
The sound source system was con-trolled by a single operator using a lap-top computer. A custom LABView™programwas used to set up and controlthe audio outputs. Time-delayed in-puts to each transducer could be usedto effectively steer the output beam toa desired elevation angle as required. Acalibrated reference hydrophone wasused to validate source performanceand provide a degree of passive acous-tic monitoring when the ship was sta-tionary. Both the output signal and thesignal received from the hydrophonewere recorded, along with an Inter-range instrumentation group (IRIG)time signal derived from a GPS satel-lite, to allow precise signal reconstruc-tion following CEEs.
The individual amplifier gains wereset to maximum output rather than auniform channel-to-channel output.This choice was made because it pro-vided the maximum acoustic powerrather than a finely shaped directionalacoustic beam response. Each ampli-fier was driven with the same am-plitude signal (no shading), but theoption for shading was available in thesoftware. Given the nature of the exper-iment and unpredictable nature of ani-mals moving in a three-dimensionalenvironment, an omnidirectional sourcewould have been preferred. However,the acoustic power for an omnidirec-tional source with a 210-dB source
FIGURE 1
Schematic of system elements of SOCAL-BRS VLA sound source.
July/August 2012 Volume 46 Number 4 51
level is 8 kW, resulting in electricalpower demands of >15 kW. Large,single-transducer solutions are possi-ble, but the transducer costs are quitehigh (>$100,000 k) and require cus-tom high-power amplifiers, each ofwhich are inconsistent with the designand objectives of the project.
Following a series of successfulbench tests of the source elementsand power configurations, the soundsource array was tested and calibratedat both the Dodge Pond and SenecaLake Test Facilities operated by theNaval Undersea Warfare Center. Thesound source was also deployed, tested,and calibrated in the field ahead of itsuse in CEEs during SOCAL-10 (thefirst year of the SOCAL-BRS projectin 2010). The results of these calibra-tions and the performance of the sourcein SOCAL-10 CEEs (and minor mod-ifications for continued successful usein SOCAL-11) are described in greaterdetail below, but each was successfuland within specifications. The engineer-ing objectives of repeatedly producingloud, short-duration, midfrequencysignals from a small source deployedand operated from a relatively small re-search vessel were met. This enabledthe entire project to have a much leanerand more agile configuration relativeto previous related efforts.
Overall ExperimentalConfiguration
Like previous BRS efforts involvingsimulated sonar (see Tyack et al.,2011), the SOCAL-BRS involved amultidisciplinary research team. Thisincluded visual monitoring and animalphoto-identification capabilities onboth the central research vessel andthe small (∼6 m) rigid-hull inflatableboats (RHIBs), animal tagging teamsbased on RHIBs, a geographical infor-mation system specialist, an acoustic
engineer, and a chief scientist on thecentral research platform. Highly ex-perienced scientists and engineers ineach of these areas used state-of-the-art tools and technologies to tag andtrack marine mammals and safely con-duct CEEs.
Because of the greatly reducedlogistical and space requirements forthe sound source, the central researchvessels used were much smaller thanin previous studies. Two phases ofSOCAL-10 were conducted, the firstbased on a 22-m recreational dive ves-sel (the M/V Truth operated by TruthAquatics in Santa Barbara, CA) andthe second from a relatively small(35 m) oceanographic research vessel(the R/V Robert Gordon Sproul oper-ated by Scripps Institution of Ocean-ography in San Diego, CA). Becauseof its smaller size, greater versatility,and reduced cost of operation, theTruth was selected as the central hubof research operations and soundsource vessel for both phases ofSOCAL-11.While the central researchplatforms from which operations wereconducted and experimental soundswere transmitted were much smallerthan previous studies, the opposite ap-proach was taken regarding small boatoperations.
In previous studies, operationswere primarily based off the main plat-form or a nearby satellite boat untilanimals were located and (in mostcases) a single very small (<5 m) inflat-able boat with ∼25 HP engine ap-proached animals for tagging. Incontrast, SOCAL-BRS put a premiumon the use of two larger andmuch fasterRHIBs capable of covering large areasindependent of the central vessel. Theresulting configuration, while similarin overall nature to previous studies,was more spatially dispersed and ableto cover larger areas. Additionally,
operational teams on the RHIBs werealways on the water, ready to respondimmediately given tagging opportuni-ties. The research vessel carrying thesound source remained close enoughto the RHIBs that it could transit toeither, once animals were tagged andconditions were suitable for CEEs tobe conducted.
CEE MethodologyThe overall objective of SOCAL-
BRS is to better understand basic behav-ior and responses of different marinemammals to sound exposure in orderto inform operational and manage-ment decisions about active sonaruse. Since sounds similar to thosebeing tested had previously beenfound to harm somemarinemammals,care was taken to ensure that animalswere not injured during the conductof the research (see Boyd et al., 2008).Consequently and in accordance withpermitting authorization for this work(U.S.NationalMarine Fisheries Servicepermit #14534 issued to N. Cyr withB. Southall as chief scientist, ChannelIslands NationalMarine Sanctuary per-mit #2010-004 issued to B. Southall,and a consistency determination fromthe California Coastal Commission), anumber of conditions for initiating andconducting CEEs were put in place.
The SOCAL-BRS CEE protocolswere derived from those used in theBahamas BRS study (see Tyack et al.,2011). However, SOCAL-10 and -11selected a greater variety of focal spe-cies. These included not only certaintoothed cetaceans (e.g., Cuvier’sbeaked whale [Ziphius cavirostris] andRisso’s dolphin [Grampus griseus])but also several large baleen whale spe-cies (e.g., blue whales [Balaenopteramusculus]). Because the operationalconfiguration included two capableRHIBs, multiple tagged animals were
52 Marine Technology Society Journal
often involved in experimental trials.Requisite modifications and adapta-tions of the CEE methods and proto-cols are described below.
The following conditions were metprior to beginning CEEs. Acousticmonitoring tags had to be attachedfor a sufficient duration to reduce at-tachment disturbance effects and ob-tain a reasonable amount of baselinebehavioral data. For baleen whales,this was aminimumof 45min, whereasfor toothed species, a 2-h baselineperiod was selected. Field personnelalso had to confirm that there wereno neonate calves in either the focalgroup or any groups that would be in-cidentally exposed; neonate statuswas defined by the presence of fetalfolds for most species, but by age of∼6 months for endangered species.The sound source could not be oper-ated within 1 nm of any landmassor within 3 nm of land within theChannel Islands National MarineSanctuary. Additionally, the soundsource could not be operated within10 nm from the site of any previoussound transmissions on the same day.Finally, operational conditions (e.g.,weather) had to support both success-ful completion of CEE and interpreta-tion of results, as well as postexposuremonitoring before CEEs could begin.
Provided these conditions were met,researchers would initiate CEEs. Thesound source vessel was positioned∼1,000 m from a focal tagged ani-mal, accounting for group movement/distribution to the extent possible. Thesource was deployed from the sternof the vessel while in a stationary po-sition, which significantly reducedengine noise. Only small position ad-justments were required to maintain avertical orientation of the sound source.In cases where multiple animals weretagged, the source was positioned as
described above in relation to one in-dividual and the other was typicallyfurther away. The source was then de-ployed to a specified depth (∼30 m),and a minimum of four trained marinemammal observers would conduct andmaintain a 360° visual survey to ensurethat no marine mammals were within a200-m “safety” radius of the sourcevessel during transmissions.
Either simulated MFA sonar orpseudorandom noise (PRN) signalsin the same 3-4 kHz band were thentransmitted at a starting source levelof 160 dB at 1 m, with one transmis-sion onset every 25 s ramped up by3 dB per transmission to maximumoutput levels for each signal. The useof sound ramp-up protocols and rela-tively low starting levels were requiredconditions of the environmental per-mitting for this research. The ramp-up rate was selected to cover the largerange of source output levels (∼50 dBtotal range) within a reasonable timeperiod given the other methodologicalprotocols, but it should be noted thatthis is an aspect of SOCAL-BRS expo-sures that is different than exposure toa real military source; such a quickramp-up could be interpreted as arapid approach of a moving source.The MFA signal was 1.6 s in total du-ration, consisting of a 3.5- to 3.6-kHzlinear FM sweep (0.5 s), then a3.75-kHz tone (0.5 s), a 0.1-s delay,and finally a 4.05-kHz tone (0.5 s); itwas projected at a maximum sourcelevel of 210 dB at 1 m. The dutycycle and waveform of the MFA signalwere designed to be similar to some ofthose used by the U.S. Navy in theirSQS-53C tactical midfrequency sonarsystems; these systems use a variety ofsignals and operational configurations,but these parameters for the simulatedsonar signals were within these condi-tions according to information provided
by the Navy. The PRN signal was de-signed with generally similar featuresto the MFA signal, but lacking thetonal characteristics and frequencymodulation patterns. The PRN signalwas 1.4 s in total duration, consistingof 3.5- to 4.05-Hz band-limitednoise (1.0 s), a 0.1-s delay, and finally3.5- to 4.05-Hz band-limited noise(0.3 s); it was projected at a maximumsource level of 206 dB at 1 m. Trans-mitting this broader band signal atidentical output characteristics to theMFA signal was not possible due topower limits of the source. The sourcewas, however, extremely flexible interms of capabilities to project a widevariety of sound stimuli within itsfunctional bandwidth, enabling anadaptive approach if alternate wave-forms were selected for use.
Transmissions of either signal type(each CEE consisted of only one) con-tinued once every 25 s at the respectivemaximum source level for a total trans-mission time of 30 min, unless anycontra-indicators required an earlyshutdown. These included any marinemammal observed within 200m of thesound source and any abnormal behav-iors indicating a potential for injuryor clear separation of mothers and de-pendent offspring.
Following CEEs, post-exposuremonitoring was conducted from boththe source vessel and the RHIBs. It in-cluded visual scan surveys and (in mostcases) passive acousticmonitoring of theimmediate playback area using for atleast 30 min, as well as monitoring offocal groups for at least 1 h post-CEE.
Results and ConclusionsSound Source Developmentand Testing
The SOCAL-10 source was suc-cessfully tested and calibrated at the
July/August 2012 Volume 46 Number 4 53
NUWC Seneca Lake Test Facility on11–12 August 2010. Full verticalbeam patterns and source level mea-surements were taken. Peak resonancewas measured at 3.8 kHz at a maxi-mum source level of 210.5 dB with a−3 dB beam-width of ∼8° (Figure 2).
Beam patterns were measured atdepression angles of 0°, 10°, 15°, and30°. The higher the steering angle,the higher the side lobes, which re-sulted in higher energy over a broaderrange of depths during CEEs. At a 15°steering angle, an average level of ap-proximately 202 dB was maintainedfrom 0° to 60° with an on-axis levelof 210 dB (Figure 3).
Note that the individual transduceroutput levels were maximized ratherthan matched to each other. This gen-erally results in the highest outputpower and relatively more prominentside lobes compared with a well-matched line array sound source. Inthis application, higher side lobeswere not detrimental because a rela-tively omnidirectional beam patternwas desirable. Since the methodologi-cal protocols included measuringreceived exposure levels on animal-borne tags, it was much less criticalthat the animal be directly in the
main lobe with a higher and knownsource level with which to estimate ex-posure. Rather, a relatively broaderbeam pattern was selected, yielding amore diffuse sound field in which theexposure goal of 100-160 dB RMS re-ceived sound level could be met over a
broader area. Exposures of multiplespecies were generally near-surface(<200 m), with the exception of thetwo Cuvier’s beaked whales.
Following the Seneca Lake calibra-tions, the sound source was successfullytested in the field and used duringCEEs in SOCAL-10 and -11. Spectro-grams and relative transmit voltages foreach signal type, as transmitted fromthe control computer to the source,are given in Figure 4. Deploymentwas successfully and safely conductedboth by hand from the smaller dive ves-sel (R/V Truth) and via a conventionalA-frame aboard the larger researchvessel (R/V Robert Gordon Sproul ).Deployment and recovery time was ap-proximately twice as fast (∼4min) whenconducted by hand on theM/V Truth.Based on measurements made within10 m of the sound source with a cali-brated hydrophone and simple spread-ing loss calculations, transmissionsin the field were consistent with theSeneca Lake calibration in terms of cal-culated source levels.
While stimulus waveforms andsource output levels were precisely re-produced as expected, some problemswere encountered in the temporalspacing of transmission sequencesdue to D/A hardware errors. Trans-mitted waveforms recorded from amonitoring channel showing signalssent from a control computer to thesource for a typical sound transmissionsequence in SOCAL-10 (Figure 5)show the resulting irregularities inthe planned 25 s signal onset dutycycle typical of some sequences inSOCAL-10.
As evident in this figure, these ir-regularities did not affect the relativetransmit levels in the ramp-up orfull power signals or the total dura-tion of transmissions. The D/A cardwas subsequently replaced following
FIGURE 2
Source level from 2 to 7 kHz calibrated for a maximum output of 210 dB re: 1μPa (RMS).
FIGURE 3
Vertical beam pattern curves for the 15 ele-ment array with 15° beam steering (top) andwith the array steered to 0° elevation angle(bottom), which was the nominal configurationin the field. With the array vertically deployed,90° is oriented up; 0° and 180° are orientedhorizontally.
54 Marine Technology Society Journal
SOCAL-10, and the timing irregulari-ties were eliminated for SOCAL-11.
Calibrated measurements of bothsignal types were made during SOCALBRS CEEs using the source moni-toring hydrophone and the acoustictags. Figure 6 shows a single transmis-sion of an MFA signal recorded duringSeneca Lake calibrations, along withan MFA signal recorded on a bluewhale during a CEE. The transmittedsource level of 210 dB at 1 m, whichwas extremely consistent across manytransmissions during calibration test-ing, resulted in a received level (maxi-mum RMS level in any 200 msanalysis window over the 1/3 octaveband centered at 3.7 kHz; details ofthe RL analysis methods were as
reported in Tyack et al., 2011) of156 dB on the animal. Precise dis-tances to focal animals for any trans-mission were difficult to determine,especially when the animal was sub-merged and not visible, since the tagsused did not transmit any positionalinformation. However, the estimateof horizontal range from this animalto the sound source for the sightingclosest to the time of this transmissionwas approximately 1400 m. As is evi-dent, signal characteristics were wellpreserved in the received signal on theanimal, with the expected reverberationpatterns evident, and the maximumoutput level resulting in a receivedlevel for this individual transmissionnear the top of the target range.
Similar results were obtained withthe PRN signal. A single PRN trans-mission recorded during Seneca Lakecalibrations is plotted with a signal re-corded on another blue whale during adifferent CEE in Figure 7. The trans-mitted source level of 206 dB at 1 mresulted in a maximum received levelof 152 dB on the animal (measuredas described earlier for the MFA sig-nal). Again, precise distance to the an-imal for any transmission is difficult todetermine, but the estimated horizon-tal range from the animal to the soundsource for the sighting closest to thetime of this transmission was approxi-mately 1,600 m. As for the MFA sig-nal, the PRN characteristics are wellpreserved in the received sound wave-form on the animal, some reverbera-tion is present, and the received levelsare near the upper end of the targetrange using the maximum sound out-put level.
The above examples demonstratethe efficacy of the source performance,experimental methodology, and opera-tional configuration to result in signalsreceived by individual free-rangingmarine mammals within specifiedparameters and exposure levels. Thesound source was notionally posi-tioned approximately 1,000 m fromfocal animals during CEEs, but ani-mals frequently moved just prior toor during transmissions or, in somecases, two animals were tagged andthe source vessel maneuvered to thetarget range from one of the two.Tagged individuals were consequentlybetween about 500 and 4,000 m dur-ing CEE transmissions. Given the50-dB dynamic range of source outputlevels, the inherent variability in soundpropagation in different conditionsacross CEEs, relative animal and tagposition during CEEs, and other fac-tors, received exposure levels differed
FIGURE 4
Spectrograms of individual MFA (A) and PRN (B) signals (amplitude is in relative voltage) sent fromthe control computer to the sound source. Individual signal elements were projected at differentoutput voltages corresponding to different target source levels within a transmit sequence.
FIGURE 5
Waveform display from a monitoring channel showing signals (in relative voltage) sent fromcontrol computer to sound source during a CEE; the transmit sequence (typical for both signaltypes) shows the ramp-up to full power and ~30 min transmission interval.
July/August 2012 Volume 46 Number 4 55
across subjects and species. However,despite all these sources of variability,received levels for the multiple individ-uals and species tested clearly fall withinthe specified target range (100-160 dB)of received levels (Figure 8). These re-sults are presented in order to show thegeneral patterns of exposure relative tospecified target levels rather than indi-vidual exposure patterns or changes inbehavior as a function of exposure.
Received levels for MFA signals aregenerally slightly higher than PRN,likely the result of the 4 dB differencein maximum source levels between thetwo stimuli. Additionally, received lev-els were distributed across the rangeof target levels. Obtaining these vari-able exposure levels within individualsof a focal species (three of the five testedare shown above) is an element of theexperimental design, as it enablesassessments of behavioral response asa function of exposure level. Receivedlevels across the full target range wereachieved in the 26 blue whale CEEs.For the odontocetes cetaceans tested,somewhat lower maximum receivedlevel conditions were experienced,
although it should be noted that thesample sizes are considerably less (sixRisso’s dolphins and two Cuvier’sbeaked whales). Additionally, most ofthese exposures were measured with anewer version DTAG using acousticcalibration data obtained from asmall number of the new tags; morecomprehensive calibration of the newtags could necessitate small corrections
to the reported levels, although theseare not likely to change the general pat-tern of lowermaximum exposure levelsin the odontocete versus mysticetecetaceans.
In summary, the custom-designedVLA sound source developed forSOCAL-BRS was successfully tested,calibrated, and used in the context ofCEEs. It met or exceeded almost all
FIGURE 6
Spectrogram displays of a single MFA signal transmission. (A) Re-corded with a calibrated reference hydrophone at 22.3-m range (levelsreferenced to 1-m range) using 210 dB RMS source-level output setting.(B) Recorded from a calibrated DTAG attached to a blue whale on 3 Sep-tember 2010 during a SOCAL-BRS CEE sequence (max RMS level in any200 ms analysis window was 156 dB; see text for additional details).[Note both figures have a 50-dB color scale range but ranges differ be-tween plots].
FIGURE 7
Spectrogram displays of a single PRN signal transmission. (A) Re-corded with a calibrated reference hydrophone at 22.3 m range (levelsreferenced to 1-m range) using 206 dB RMS source level output setting.(B) Recorded from a calibrated DTAG attached to a blue whale on23 Sept 2010 during a SOCAL-BRS CEE sequence (max RMS level inany 200ms analysis window was 152 dB; see text for additional details).[Note both figures have a 50 dB color scale range but ranges differ be-tween plots].
FIGURE 8
Histograms showing relative proportions (within species) of received levels (in 5 dB bins) ofMFA and PRN signals measured with calibrated DTAGs during SOCAL-BRS CEE sequencesfrom 2010 and 2011 for 26 blue whales (top), 6 Rissos dolphins (middle), and 2 Cuvier’sbeaked whales (bottom; MFA only).
56 Marine Technology Society Journal
design specifications and was easilyhand-deployed from a small researchvessel. This proved to be a critical en-abling factor in the overall effort to re-duce the overall size, complexity, andflexibility of the experimental method-ology. Future efforts are underway toreduce source size even further, partic-ularly on the dry end of the system, toenable deployment from even smaller(∼10 m) boats while maintaining thesame output characteristics.
Summary of Accomplishmentsand Assessment of OverallExperimental Configuration
Within the first two seasons ofSOCAL-BRS, efforts to reduce theoverall size, cost, logistical complexity,and rigid schedules of earlier studieswhile maintaining a comparable exper-imental paradigm and maximizing sci-entific results were quite successful.The research team had a similar inter-disciplinary configuration as previousprojects but involved approximatelyhalf as many people and approximatelyone-third the total cost. During thecourse of the first 2 years of the exper-iment (SOCAL-10 and -11), a totalof 101 tags of six different types wereattached to 79 individuals of at leasteight different marine mammal spe-cies (see Southall et al., 2011, 2012,for additional details). Tags were suc-cessfully attached to at least onemarine mammal (and in many casesmultiple animals) on 77% of allSOCAL-BRS operational field days(39/51 days) of the first two fieldseasons.
Additionally, a total of 46 CEEswere successfully completed (on 61%of all SOCAL-BRS operational fielddays, 31/51 days) involving individ-uals of five marine mammal species,which was a level of productivity and
species diversity well beyond expecta-tions based on the results of previousefforts. Additionally, SOCAL-BRSconducted the first ever CEEs onCuvier’s beaked whale, which is thepredominant species represented inprevious stranding events involv-ing military sonar. Furthermore, theSOCAL-BRS experimental configura-tion enabled multiple tags to be de-ployed on individuals of some species(notably blue whales) with prolongedfocal fol low data from multipleRHIBs on different animals at differ-ent ranges from the sound source dur-ing CEEs. Received sound levels for allspecies tested achieved the target rangespecified prior to CEEs. Exposures formysticete cetaceans were distributedacross the 100–160 dB range whileodontocete received levels were moretypically from 100 to 140 dB. This islikely because some of the odontoceteCEEs involved subjects at greater hor-izontal range from the sound sourceand also because some individuals(most notably the beaked whales)were at much greater depths during ex-posure. Vertically down-steering thesource directivity pattern should beconsidered as a means of potentiallyincreasing received levels for deeper-diving species when their vertical posi-tion in the water column is reasonablywell known during CEEs. Detailedanalyses of exposure conditions andbehavioral responses are not presentedhere but are ongoing, and some initialresults are available (DeRuiter et al.,2011;Goldbogen et al., 2011; Southallet al., 2011, 2012).
Key developments in SOCAL-BRSincluded the use of a smaller primaryresearch vessel enabled by a smaller,more easily handled sound sourceand the decentralized approach withlarger, faster, and more wide-rangingRHIBs working on the water at all
times. These changes in configurationand the general mode of operation,which allowed selection of focal speciesand areas based on the weather and an-imal availability, clearly resulted in theintended increase in the number ofanimals tagged and total CEEs success-fully completed. However, in compar-ing the SOCAL-BRS results withother previous and ongoing behavioralresponses studies involving activesonar, there are a number of importantconsiderations.
For instance, 46 CEEs were com-pleted in SOCAL-BRS compared tofive in the Bahamas BRS (each with acomparable number of field days intwo seasons), but an equal number ofbeaked whale CEEs were conducted ineach study (two total) albeit on dif-ferent beaked whale species. TheBahamas effort was almost entirelyfocused on beaked whales, whileSOCAL-BRS focused on beakedwhales during the relatively rare timesweather conditions were suitable andmaintained options to work on otherimportant species nearby at othertimes. The increased success rate ofthe first phase of the 3S field seasons(14 CEEs in three field seasons) alsoappears to be a function of havingmultiple options for focal species, in-cluding some easier to tag species,and operational areas. It should alsobe noted that the 3S configurationdoes enable the use of an actual opera-tional sonar system used in militarytraining operations and capable ofbeing towed; the SOCAL-BRS con-figuration resulted in less realisticsimulated exposures because of the in-ability to tow the sound source.
Clearly there are area- and species-related characteristics that favor differ-ent methodological and operationalconfigurations to best address thesechallenging field research questions.
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The approach selected for SOCAL-BRS appears to have worked well forthe objectives identified and the fieldconditions encountered, but it is byno means the ideal approach for all cir-cumstances. Subsequent efforts willlikely be increasingly adaptive andsmaller in the overall configuration ofresearch teams. Furthermore, evolu-tion toward exposure conditions thatare more similar to real-world expo-sures to human sound are increasinglyimportant to add to the growingknowledge of response to scaled-down sources. These two progressionsare not necessarily in conflict with oneanother but will require increasingcollaboration between the researchand military communities to addressapplied questions about the real risksof impact from operations to marinemammals. Advances in acoustic andother technologies will continue to en-able these and other refinements ofexperimental methodologies to ad-dress key biological and managementresearch questions.
AcknowledgmentsThe authors would like to especially
acknowledge the tireless and excep-tional efforts of the entire SOCAL-BRS field and analytical teams. Over40 individuals have been directly in-volved in planning, completing, andassessing the results of SOCAL-BRS,and this project would not have beenpossible without them. We wouldalso like to thank the project sponsors,the U.S. Navy Chief of Naval Opera-tions, Environmental Readiness Pro-gram under Drs. Frank Stone andBob Gisiner and the Office of NavalResearch Marine Mammal Programunder Dr. MikeWeise. We also appre-ciate the support and collaboration ofthe U.S. Navy’s SCORE range based
on San Clemente Island. Discussionsregarding experimental design andprotective measures with the U.S.Marine Mammal Commission andthe California Coastal Commissionswere particularly helpful as well.Finally, various staff in NOAA’s Na-tional Marine Fisheries Service (Officeof Protected Resources, SouthwestFisheries Science Center), SouthwestRegional Stranding Network, andChannel Islands Marine Sanctuarywere also extremely instrumentalthroughout the project.
Corresponding Author:Brandon SouthallSouthall EnvironmentalAssociates, Inc.9099 Soquel Dr., St. 8,Aptos CA, 95003Email: [email protected];www.socal-brs.org
