Interspecific Communicative and CoordinatedHunting between Groupers and Giant MorayEels in the Red SeaRedouan Bshary1*, Andrea Hohner1,2, Karim Ait-el-Djoudi1, Hans Fricke3,41 Department of Zoology, University of Neuchaˆtel, Neuchaˆtel, Switzerland, 2 University of Cambridge, Department of Zoology, Cambridge, United Kingdom, 3 Max-Planck-Institut fu¨r Verhaltensphysiologie Seewiesen, Starnberg, Germany, 4 Leibniz-Institut fu¨r Meereswissenschaften (GEOMAR), Universita¨t Kiel, Kiel, GermanyIntraspecific group hunting has received considerable attention because of the close links between cooperativebehaviour and its cognitive demands. Accordingly, comparisons between species have focused on behaviours that canpotentially disting uish between the different level s of cognitive complexity involved, such as ‘‘intentional’’communication between partners in order to initiate a joint hunt, the adoption of different roles during a jointhunt (whether consistently or alternately), and the level of food sharing following a successful hunt. Here we reportfield observations from the Red Sea on the highly coordinated and communicative interspecific hunting between thegrouper, Plectropomus pessuliferus, and the giant moray eel, Gymnothorax javanicus. We provide evidence of thefollowing: (1) associations are nonrandom, (2) groupers signal to moray eels in order to initiate joint searching andrecruit moray eels to prey hiding places, (3) signalling is dependent on grouper hunger level, and (4) both partnersbenefit from the association. The benefits of joint hunting appear to be due to complementary hunting skills, reflectingthe evolved strategies of each species, rather than individual role specialisation during joint hunts. In addition, thepartner species that catches a prey item swallows it whole immediately, making aggressive monopolisation of acarcass impossible. We propose that the potential for monopolisation of carcasses by one partner species representsthe main constraint on the evolution of interspecific cooperative hunting for most potentially suitable predatorcombinations.Citation: Bshary R, Hohner A, Ait-el-Djoudi K, Fricke H (2006) Interspecific communicative and coordinated hunting between groupers and giant moray eels in the Red Sea.PLoS Biol 4(12): e431. DOI: 10.1371/journal.pbio.0040431IntroductionCooperative hunting, i.e., the increase in successful preycapture observed when two or more individuals engage in ahunt, has been demonstrated in a wide variety of species [1–4]. In many cooperatively hunting species, hunts can best bedescribed as opportunistic, simultaneous individual hunts [4],in which each animal tries to maximise the probability ofcatching the prey for itself. True coordination, as defined in[5], exists only if individuals play different roles during ahunt. Role differentiation implies that individuals will adoptroles that have a lower probability of personal success or ahigher risk of injury than other roles would offer, e.g., huntswhere some individuals act as chasers while others block theescape routes of prey. Such coordination is known for only ahandful of species [5–8], all of which are mammals or birds.Individual role specialisation within coordinated hunts iseven more rare and has only been observed in two studies todate [7,8]. Communication between group members toinitiate a coordinated search for suitable prey (for whichthe term ‘‘ intentional hunting’’ has been used) is known onlyfrom a single population of chimpanzees [5]. The samepopulation of chimpanzees is also well known for respectingprey ownership, where the successful individual shares withcohunters [5]. While simultaneous feeding on a prey carcassmay also occur in carnivores, access in these species is bestpredicted by individual rank and/or nepotistic toleration ofrelated lower ranking individuals [4].Here we describe interspecific and communicative huntingbetween the grouper, Plectropomus pessuliferus, and the giantmoray eel, Gymnothorax javanicus, observed in the coral reefs ofthe Red Sea. Groupers are diurnal predators, whereas themorays are nocturnal hunters and usually rest in crevicesduring the day. The hunting strategies of the two predatorsare also very different. Groupers are semi-benthic piscivors,which hunt in open water. In order to avoid predatorygroupers, reef fish hide in corals (apart from pelagic prey likefusiliers). Moray eels, in contrast, sneak through crevices inthe reef and attempt to corner their prey in holes.Consequently, the best strategy for prey to adopt in orderto avoid moray predation is to swim into open water. Thehunting strat egies of the t wo predators are thereforecomplementary, and a coordinated hunt between individualsof the two species confronts prey with a multipredator attackthat is difficult to avoid [9]; prey are not safe in open waterAcademic Editor: Frans de Waal, Emory University, United States of AmericaReceived March 20, 2006; Accepted October 13, 2006; Published December 5,2006DOI: 10.1371/journal.pbio.0040431Copyright: Ó 2006 Bshary et al. This is an open-access article distributed under theterms of the Creative Commons Attribution License, which permits unrestricteduse, distribution, and reproduction in any medium, provided the original authorand source are credited.* To whom correspondence should be addressed. E-mail: [email protected] Biology | www.plosbiology.org December 2006 | Volume 4 | Issue 12 | e4312393PLoSBIOLOGYbecause of the grouper hunting strategy but cannot hide increvices because of the moray’s mode of attack.Here we first provide some descriptive information on theinteractions b etween the two predators (i.e., frequency,duration, and distance between partners during a joint hunt)and use a simplified version of Waser’s gas model [10] to showthat associations are not due to random encounters. Second,we describe the signals produced by the groupers that serveto elicit joint hunting. Third, we present experimentalevidence that the production of these signals is inhibited ifthe grouper is satiated. Finally, we present observationalevidence that both partners increase their hunting successwhen they are in association. We then discuss the selectiveconditions that might promote such an unusual interspecificcooperation.ResultsEvidence That Associations Are NonrandomBecause the exact number of moray eels in our study area isunknown, we compared the distribution of observed dura-tions of