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Mediterraneanstripeddolphinsshareecholocationinformationduringtravelingandforaging.

Marianna Anichini * 1,2, Cristina Giacoma2, Elena Papale1,2, Marta Azzolin1,2

1Gaia Research Institute Onlus. Italy2University of Torino, Dip. Biologia Animale e dell'Uomo, V. Accademia Albertina, 13, 10125 Torino, Italy

* mary.anichini@gmail.com

Discussion

References

IntroductionWho?

FreerangingStripedDolphin(Stenella coeruleoalba),one ofthemostwidespreadcetaceanspeciesintheMediterraneanSea,isanextremelyvocalmammalianspeciesbutitsvisualandacousticbehaviourisalmostunknown.(FIG1).

Where?GulfofCorinth(GOC),Greece.ThestudyareaislocatedbetweenthePatra strait,openingontheIoniansea,andtheCorinthCanal

ontheAlkyonides gulf.Anareaofabout700km2 hasbeencovered(FIG2).

When?DuringthemonthsofJulyandAugust2009and2010.

Why?Inordertounderstandandanalyze howStenella coeruleoalba echolocationclicksratechangesinrelationtofocalgroupsizeand

behavioralcontext.

Results

Materials and methodsDuringthisresearch,63vesselbasedsurveyshavebeencarriedoutintypicalweatherconditionandecologicandanthropogenicparameterswere recorded every 15minutes.During sightings, group size and interactionwith boatswere collected every 3minutes. The animal surface behaviour was analyzed using the focal group sampling methodology (Altmann,1974), andfollowinganethogram createdbeforeandduringthestudy:41behaviours and4differentvocaltypewererecorded,thanksalsoto those already developed in previous studies on Atlantic spotted dolphins (Herzing,D.L.,1996; Dudzinski,K.M.,1996). Groupdimensionwasdividedinfourcategories:1)15;2)69;3)1015;4)2030animals.Soundswererecordedintheproximityofthefocalgroup(maxdistance100m)withasinglehydrophoneatasamplingfrequencyof96kHz(16bitmonochannel)connectedtoadigitalaudioMAudiomicrotrack recorder.Inordertoreducethelowfrequencybackground noise a filter at 1kHz was used during recordings. Striped dolphin clicks have been classified in four qualitiescategories(03):onlysignalsclearandaudible(23quality)wereconsidered.Inordertosynchronizevisualandacousticbehaviour,recordingshavebeensubdividedinintervalsof3minuteseach.Foreachinterval,onlytheclicksdetectedinthefirst10secondswereconsideredforanalysisandonlythemostfrequent(numberof times inwhich appears the behavior / number of total behavioral sequences in intervals of 3minutes) behavioral states(normalswimtailout,raftingandsharking) relatedtothemaincategoriesofTravelling andForagingwereincluded.

Statistical analysis (KruscallWallis Test) showed that the echolocation clicks ratewas significantly affected by group size. The echolocation clicks production perdolphin(clicks/minute/animal)isminimuminthebiggestgroupsize.Jones and Sayigh (2002), have reported how the bottlenose dolphin in largergroups,emitted lessofecholocationclicksperunitoftime,sharingtheechoesoftheotheranimals(Tyack,1997).Statistical analysis (Rho Spearmans Test) showed also, a positive and significantcorrelation of the click rate in relation to behavioral state linked to forage andtravelactivities, indicatingthatecholocation isused inforagingandtravelling.Wesuggest that theseresults,support the idea thatecholocation informationcanbeshared by the animals in a larger group above all during specific behavioralactivitiesasforagingandtravelling.

Altmann,J.(1974).Observationalstudyofbehavior:samplingmethods. Behav.ior 49,227267.Dudzinski,K.M.(1996).CommunicationandbehaviorintheAtlanticspotteddolphins(Stenella frontalis):relationshipsbetweenvocalandbehavioralactivities.Ph.D.Dissertation.TexasA&MUniversity.Herzing,D.L.(1996).Vocalizations andassociated underwater behavior offreeranging Atlantic spotted dolphins,Stenella frontalis andbottlenose dolphin,Tursiops truncatus.Aqua.Mamm. 22,6179.Jones,G.J.,andL.S.Sayigh.(2002).Geographicvariationinratesofvocalproductionoffreerangingbottlenosedolphins.MarineMammalScience18:374.393Tyack,P.(1997).Studyinghowcetaceansusesoundtoexploretheirenvironment.PerspectivesinEthology 12:251297.

Fig.3.SpectrogramOFcliks (quality3)obtainedbythesoftwareAdobeAudition3.0WITHaFFTsizeof256pointsINHammingwindow.

Fig.2.Studyarea:GulfofCorinth(GOC),Greece.

Fig.1.StripedDolphin(Stenella coeruleoalba)

Fig.5.Scatterplotshowingtherelationbetweentheclicks/minute/Aandthedifferentgroupdimension.

Sightings 44Meansightingsfrequency

FREQ=nsightings/hourssurvey0,5

Hoursofbehavioral observationsandsimultaneousrecordings

3,5

Echolocationclickstotallydetectedinthefirst10sforeachinterval(FIG2)

5015

Fig.4.Scatterplotshowingtherelationbetweentheclicks/10andthedifferentgroupdimension.

Both the relationships between group size category (number of animals) and theecholocationclicks(clicks/minute)andthosedividedforthenumberofanimals(numberofclicks/minute/animals),wereexamined.ThenonparametricKruscallWallisTestshowedasignificantdifference(P

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