Identifying foraging events in deep diving southern elephant seals, Mirounga leonina, using acceleration data loggers

Southernelephantseals(Miroungaleonina) rangewidelythroughouttheSouthernOceanandare associatedwithimportanthabitats(e.g., iceedges,shelf)wheretheyaccumulateenergytofueltheir reproductiveeffortsonland.Knowledgeofthefinescaleforagingbehaviourusedtogarnerthisenergy, however,islimited.Forthefirsttime,accelerationloggersweredeployedonthreeadultsouthern elephantsealsduringatranslocationstudyatKerguelenIsland.Theaimsofthestudywereto (1) identifypreycaptureattemptsusing2-Daccelerometertagsdeployedontheheadofsouthern elephantseals,(2)comparethenumberofforagingdivesidentifiedbysimpledivedepthprofilesand accelerometerprofilesand(3)comparedivecharacteristicsbetweenpreyencounterandnon-prey encounterdives.The2-Dloggersrecordeddeptheverysecond,surgeandheaveaccelerationsat8or 16 Hzandwerecarriedforperiodsbetween23and121h.Rapidheadmovementswereinterpretedto be associatedwithpreyencounterevents.Accelerationdatadetectedpossiblepreyencountereventsin 39–52%ofdiveswhilst67–80%ofdiveswereclassifiedasforagingdiveswhenusingdivedepthprofiles alone. Preyencountersoccurredinsuccessivedivesduringdaysandnightsandlastedbetweentenths of asecondand7.6min.Binomiallinearmixedeffectmodelsshowedthatsealswerediving significantlydeeperandincreasedbothdescentrateandbottomdurationwhenencounteringprey. Dive duration,however,didnotsignificantlyincreaseduringdiveswithpreyencounters.Theseresults are inaccordancewithoptimalforagingtheory,whichpredictsthatdeepdiversshouldincreaseboth their transitratesandthetimespentatdepthwhenaprofitablepreypatchisencountered.These findings indicatethatthistechniqueispromisingasitmoreaccuratelydetectspossiblepreyencounter eventscomparedwithdivedepthprofilesaloneandthusprovidesabetterunderstandingofseal foragingstrategies.