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Trophic Ecology of Four Apex Predators in the Open Ocean Ecosys

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Trophic Ecology of Four Apex Predators in the Open Ocean Ecosys TTrroopphhiicc EEcocolologgyy ooff FFoouurr AAppeexx PPrrededaattoorrss ooff tthhee PPelaelaggicic EEcocossyysstteemm iinn tthhee IInnddiaiann OOceaceann LLaanncceett ffiisshh,, YeYelllloowwffiinn ttununaa,, BBiiggeeyyee ttununaa && SSwwoorrddffiisshh Michel Potier 1, Francis Marsac 2,, Vincent Lucas 3, Richardd SSaabbaattiiéé 4,, Oliviieerr MMaauurryy 1 ,, JJeeaann--PPiieerrrree HHaalllliieerr 1 ,, Yves Chérel 5 & Frédéric Ménard 1 1 IRD,, Reunion Island 2 IRD,, Sète,, France 3 Seychelles Fishing Authority, Seychelles 4 ENSA,, Rennes,, France 5 CNRS-CEBC, Chizé, France «« WhoWho eeaattss wwho ho ?? »» iiss aa rreelleevant aapprpproaoach to uunderstand tthhee cchaharraacctteerriissttiiccss ofof aann eeccososyysstteemm aandnd hhowow thethe ddiiffefferreentnt fufuncncttiioonanall ggrrououpsps iintnteerraacctt No food, No future …. GGooaalsls Yellowfin (Thunnus albacares) CComompaparree tthehe ddiieett ofof foufourr mmaajjoorr prpreeddaattoorrss StStuuddyy tthehe ddeeggrreeee ofof ovoveerrllaap-p- pipinngg ofof fefeeeddiingng rreeggiimmeess aammonongg prpreeddaattoorrss EEssttiimmaattee tthhee ssiizeze rraatitiosos bebettwweeeenn prpreeddaattoorrss && prpreeyy Lancetfish (Alepisaurus ferox) IIntntrroodduuccee aa ssttaablblee iissoottopeope peperrsspepeccttiivvee Swordfish (Xiphias gladius) Bigeye (Thunnus obesus) VVeerrttiiccaall DiDissttrriibbuuttiioonn :: wwhheerree ddoo ththeeyy lliiveve ?? What we know from ultrasonic tagging Thee 44 pprereddators occccuuppy 0 5 10 15 2%0 0 different depth ranges : 200 Yellowfin : 0 - 200 m Bigeye tuna : 0 – 500 m ) 400 Swordfish 0 – 700 m : m ( h t Lancet fish : ?? p De 600 800 1000 10 Status May 2004 5 0 -5 -10 -15 -20 -25 -30 (20) 30 35 40 45 50 55 60 65 T7ra0ine Palangre (497) Senne (518) SSttuuddyy aarreeaa Number of stomachs collected > 1100 SSuurrvveeyy iimmpplleemmeennttaattiioonn 1199 mmonontthshs ((AAuugg.. 0011//FeFeb.b. 0033)) 2 6677 LLLL sseetsts aandnd 1100 PPSS sseetsts 0 11 ococeeaanognogrraaphphiicc ccrruuiissee RR//VV -2 4747 CCTTDD pprrooffiilleess ((TT && DDO)O) -4 1515 mmiidwdwaatteerr ttrrawawllss -6 JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC 2001 -8 2002 Trawls No of stomachs < 5 2003 collected by 5 - 15 Total 150 111 163 PS sets longline set > 15 -10 Lancet fish Yellowfin Bigeye Swordfish Total 46 48 50 52 54 56 58 60 non-empty stomachs 128 110 17 123 378 LL %(n ebmpt) y 8 13 41 16 Size range (cm) 15 - 170 32 - 161 33 - 168 51 - 192 non-empty stomachs 34 12 46 PS %(n ebmpt) y 0 0 Size range (cm) 40-150 40-100 TThhee eennvviirroonnmmeennttaall ccoonntteexxtt :: TTempempereraattuurree && DDOO pprrooffilileses aanndd ddepeptthh rraannggee ssaampmpledled bbyy tthhee lolonnggllininee ggeaearr Temperature Dissolved oxygen Methods … 11-- DDiieettaarryy AAnnaallyyssiiss A Weighing the stomach content B Sorting in large categories Fish Molluscs Crustacea The less abundant categories (ie. molluscs and crustacea) are weighed then the main category (ie. fish) is obtained by difference C For each category Accumulated food s o r t i n g Fresh Food For each item Counting the remarkable organs Species identification, counting, measuring (otoliths, beaks, mandibles,,…) the remarkable organs or entire individuals. Reconstituted weight of the diet Methods … 22-- PPrreeyy DoDommiinnaannccee IInnddiicceess MoModdiififieedd CCosostteelllloo ddiiaaggrraamm (Amundsen et al. 1996) IIndndeexx ofof RReellaattiivvee IImmporporttaancncee ((IIRRII)) ((PPiinnkaskas eett alal.. 11971971)) IRI A (N A % PA %) FA % Number N, Weight P, Occurrence F IRI (N % P %) F % MA ethA odsA … A 33-- SiSimmiillaarriittyy IInnddeexx MoMorriissiittaa && HHoorrnn IInnddeexx ofof ssiimmiillaarriittyy (Magurrranan 19881988)) S S : total no of prey in regime of both predators aN : total no of prey in diet of predator A 2ani bni i1 bN : total no of prey in diet of predator B Cmh an : no of individuals prey i in diet predator A (da db)(aN bN) i bni : no of individuals prey i in diet predator B da , db : quadratic ratios Feeding regimes are compared by pairs of predators Varies from 0 (distinct feeding regimes) to 1 (identical) Above 0.6, C is reflecting a significant overlap Methods … 44-- SSiizzee MMeeaassuurreemmeennttss Fresh Items Morphometric Remainings relationships Crustaceans Propod (pelagic crabs) Propod (pelagic crabs) Total length Telson length Fish Standard length Otolith length Dentary length Lower rostral length Lower rostral length Cephalopods (LRL) (LRL) Methods … 55-- StStaabbllee iissoottooppee rraattiiooss 12 Intermediate trophic levels Tuna samples 10 3- 4‰ ? Prey2 ) 8 Prey1 ‰ Zoo ? ( N 5 Phyto ? 1 6 1‰ ? 4 POM 2 0 -26 -24 -22 -20 -18 -16 -14 13C (‰) Samples of main prey,, tunaa andd bbilillflfiisshheess ((wwhhititee mmuusscclele)),, sshhararkkss POM and Phytoppllaannkton collected but not yet analysed Sampling of filter feeders is underway ReRessuullttss 11 –– PPrreeyy cocompmpoossititioionn aanndd ddoominminaanncece ssttuuddiedied wwitithh tthhee IRIRII aanndd CoCossttelloello ddiaiaggrraamm YYFTFT anandd BBEETT acacrroossss ggeeaarrss 44 pprreeddaattoorrss wwiitthh lloonngglliinnee oonnllyy CComompparariisonson 22 pprreedd.. ((YFYFTT//BEBETT)) acacrroossss gegeararss :: PPSS bbllaannkk bbararss//LLLL ccoolloorreedd bbararss %IRI 0 20 40 60 80 100 % IRI 0 20 40 60 80 100 Natosquilla investigatoris Natosquilla investigatoris crustacea crab larvae Oplophorus typus Charybdis edwardsi other Myctophids Hyperiids Diretmoides parini Odontodactylus scyllarus Cubiceps pauciradiatus Scopelarchus analis Scombrids fish unknown fish Yellowfin Paralepis atlanticus Bigeye Cubiceps pauciradiatus LL = 44 p.i. unknown squids LL = 21 p.i. Paralepis atlanticus PS = 3 p.i. Ommastrephids PS = 2 p.i. Alepisaurus ferox octopods Ommastrephids cephalop. Onychoteuthids 100 %IRI 80 Yellowfin Bigeye 60 40 20 0 longline purse seine longline purse seine SSuurrffacacee ddwweelllliinngg ttuunnaa ((ooppeenn cciirrcclleess)) Dominance of Natossquiillllaa Specialisation on Scombrids (YFT) and flying squids (BET) DDeeeepp ddwweelllliinngg ttuunnaa ((bbllacackk cciirrcclleess)) YFT :: from generalized to specialisation (swim.crabs and crab larvae) BET :: generalilized feedining behaviiour CCoommppaarriissoonn bbeettwweeeenn 44 pprreeddaattoorrss,, lloonngglliinnee ggeeaarr 100% 80% others squids I 60% R I fish % 40% crustacea 20% 0% lancet fish yellowfin tuna bigeye tuna swordfish predators sp. TThhee pprrooppoorrttiioonn ooff eeaacchh pprreeyy ggrroouupp ((iinn wweett mmaassss)) amamoonngg tthhee pprreedatdatoorrss iiss ccoonnssiisstteenntt wwiitthh tthhee ppaatttteerrnn dedeppiicctteedd bbyy tthhee IRI IIRIRI bbyy pprreeyy iitteemm aanndd pprreeddaattoorr 0 20 40 60 0 20 40 60 80 Charybdis edwardsi Oplophorus typus Natosquilla investigatoris Natosquilla investigatoris Platyscelus ovoides Scopelarchus analis Phrosina sp. Paralepis atlantica Alepisaurus ferox crustacea Diaphus spp. bigeye tuna Omosudis lowei Cubiceps pauciradiatus Paralepis atlantica Lancet fish Diretmoides parini Fish larvae Onykia rancureli 154 prey Carinaria sp. 1868 prey Moroteuthis lonnberggii 18 families Alciopidae 41 families Sthenoteuthis oualaniensis fish 0 20 40 60 0 20 40 60 Crab larvae Acanthephyra sp. Charybdis edwardsi Natosquilla investigatoris Phrosina sp. Cubiceps pauciradiatus Odontodactylus scyllarus cephalop. Diretmoides parini Yellowfin tuna Other scombrids Und. Fish swordfish Cubiceps pauciradiatus Scopelarchus analis Diaphus spp. 4916 prey Sthenoteuthis oualaniensis Alepisaurus ferox 44 families Ornithoteuthis volatilis 818 prey Sthenoteuthis oualaniensis Moroteuthis lonnbergii 28 families Ornithoteuthis volatilis Ancistrocheirus lesueuri 7 cm 3 cm NNaattoossqquiuillllaa iinvenvessttiiggaattoorriiss CChaharryybbddiiss eeddwwaarrddssii (Stomatopod) (Portunidae) 10 Only documented in the Indian Ocean Demographic bursts in 1906, 1933, 1944,1967 A new episode underway since 1999 … 100 Feb-Mar 0 larvae 70 % May 2001 80 adults 60 4 cm Jul-Jan 50 7 cm Total length 60 -10 40 40 50 60 October 2001 40 30 20 20 10 Telson size 0 0 6 7 8 9 10 11 12 13 14 mm J F M A M J J A S O N D Swarming at the surface Swarming in the mixed layer ReRessuullttss 11 –– PrPreeyy ccoommppoossiittiioonn aanndd ddoomiminnaannccee ssttududiieedd wwiitthh tthhee IIRRII aanndd CCoosstteelllloo ddiiaaggrraamm 22 -- OOvvererlalapp ooff feefeeddiningg rregegiimmeses SSiimmiillarariittyy iinnddiicceess anandd cclluustesterr aannalalyysisiss YFT LL BET LL YFT PS BET PS YFT LL 1 BET LL 0.07 1 YFT PS 0.01 0.07 1 BET PS 0.02 0.08 0.99 1 Lancet fish Yellowfin Bigeye Swordfish Lancet fish 1 Yellowfin 0.05 1 Bigeye 0.14 0.07 1 Swordfish 0.25 0.03 0.55 1 SSiiggnniiffiiccanantt ooveverrllapap Cluster analysis based on IRIs Lancet fish wwiitthhiinn tthhee PSPS Swordfish VVaalluuees close to the ssiiggnniiffiiccanantt tthhrreesshhoolldd Big eye bbeettwweeeenn bbiiggeeyyee anandd Yellowfin sswwoorrdfdfiisshh 3200 3400 3600 3800 4000 4200 ADggistraegncatei od'nA gr Déigatstanionce FFiisshh PPrreeyy DDiissttrriibbuuttiioonn 0 10 20 30 40 50 60 Fish larvae swordfish Acanthuridae 10% Epipelagics Balistidae Carangidae big eye s Carapidae 0% c i Coryphaenidae g Dactylopteridae a lancet fish l Diodontidae e Exocoetidae 48% p i Hemiramphidae yellowfin Holocentridae 42% Ep Monacanthidae Ostraciidae Scombridae Scorpaenidae Tétraodontidae Alepisauridae Anoplogasteridae Mesopelagics Argentinidae s Bramidae lancet fish c Chiasmodontidae i swordfish 19% Diretmidae g 29% a Gempylidae l e Myctophidae p Nomeidae o Omosudidae s Paralepididae yellowfin e Swordfish Phosichthyidae
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