He also took several films and when Alexander View from the University of Cambridge watched them, he noticed something Share had missed. Most morays and all wrasses headed towards the grouper ’s location when they saw the signal, causing the prey to break their cover.
(The fact that the prey didn’t abandon their hiding spots beforehand shows that the headstand itself isn’t a hunting tactic.) And when the morays ignored the headstand, the groupers actually swum after their partner and either performed their “recruitment shimmy” or forcibly tried to push the eels in the right direction.
Such gestures are part and parcel of human life, but the only animals that seem to use them are intelligent ones, like chimps and other great apes, ravens, dolphins, and domestic dogs. Like a hunter bringing a dog to flush out rabbits, groupers entice moray eels to hunt with them (movie 1).
Groupers are bulky fish that hunt in daytime in the open water off coral reefs. When both hunt together, prey barely stands a chance: hide in the reef, the eel eats you; dash for open water, the grouper grabs you.
Bottle nose dolphins (Turnips adjuncts) form “political” coalitions every bit as complex as those of chimpanzees. While this may be a bit of an exaggeration, a new study on cooperative behavior by Redoubt Share and his colleagues really makes one wonder if there is anything fish cannot do.
The article describes the astonishing discovery of coordinated hunting between groupers (Plectropomus pessuliferus) and giant moray eels (Gymnothorax Granicus) in the Red Sea. It also offers quantification, which is truly hard to achieve in the field, of the tendencies involved in this mutually beneficial arrangement.
Interspecific group hunting has received considerable attention because of the close links between cooperative behavior and its cognitive demands. Accordingly, comparisons between species have focused on behaviors that can potentially distinguish between the different levels of cognitive complexity involved, such as “intentional” communication between partners in order to initiate a joint hunt, the adoption of different roles during a joint hunt (whether consistently or alternately), and the level of food sharing following a successful hunt.
Here we report field observations from the Red Sea on the highly coordinated and communicative interspecific hunting between the grouper, Plectropomus pessuliferus, and the giant moray eel, Gymnothorax Granicus. We provide evidence of the following: (1) associations are nonrandom, (2) groupers signal to moray eels in order to initiate joint searching and recruit moray eels to prey hiding places, (3) signalling is dependent on grouper hunger level, and (4) both partners benefit from the association.
In addition, the partner species that catches a prey item swallows it whole immediately, making aggressive monopolization of a carcass impossible. Citation: Share R, Honer A, Ait-el-Djoudi K, Cricket H (2006) Interspecific Communicative and Coordinated Hunting between Groupers and Giant Moray Eels in the Red Sea.
Academic Editor: Fran's de Waal, Emory University, United States of America True coordination, as defined in , exists only if individuals play different roles during a hunt.
Individual role specialization within coordinated hunts is even more rare and has only been observed in two studies to date . Communication between group members to initiate a coordinated search for suitable prey (for which the term “intentional hunting” has been used) is known only from a single population of chimpanzees .
The same population of chimpanzees is also well known for respecting prey ownership, where the successful individual shares with counters . Here we describe interspecific and communicative hunting between the grouper, Plectropomus pessuliferus, and the giant moray eel, Gymnothorax Granicus, observed in the coral reefs of the Red Sea.
Groupers are diurnal predators, whereas the morays are nocturnal hunters and usually rest in crevices during the day. In order to avoid predatory groupers, reef fish hide in corals (apart from pelagic prey like fusiliers).
Moray eels, in contrast, sneak through crevices in the reef and attempt to corner their prey in holes. Consequently, the best strategy for prey to adopt in order to avoid moray predation is to swim into open water.
Here we first provide some descriptive information on the interactions between the two predators (i.e., frequency, duration, and distance between partners during a joint hunt) and use a simplified version of Weiser's gas model to show that associations are not due to random encounters. Second, we describe the signals produced by the groupers that serve to elicit joint hunting.
Third, we present experimental evidence that the production of these signals is inhibited if the grouper is satiated. Finally, we present observational evidence that both partners increase their hunting success when they are in association.
Because the exact number of moray eels in our study area is unknown, we compared the distribution of observed durations of associations with the value predicted from a simplified version of Weiser's gas model as an acceptable compromise . The gas model yields mean association durations based on the assumption of independent movements (see Methods).
A proportion of observed durations of interactions fit the null hypothesis of random association, which predicts durations of 100 s. However, 56% of the 207 interactions lasted longer than predicted by the null hypothesis, among which 71% lasted at least three times longer (Figure 1). Observed frequency distributions of durations (min) of interactions between groupers and moray eels.
The arrow almost above the 2-min time category indicates the average duration of associations (100 s) predicted by a null model, assuming independent movements of individuals of the two species. Figure 2 shows the average distance between a grouper and a moray eel per minute of joint hunting for a single observation, where video filming allowed detailed analysis of this variable.
The two partners stayed together at a distance of between 1 and 3 times 70 cm (which is one approximate grouper body lengths) over a period of 38 min. Mean distance given as multiples of grouper body length (estimated 70 cm) between a grouper and a moray eel per minute association, analyzed on screen from a 38-min film clip of a joint hunt that was already ongoing when the camera man joined.
The gap in the data is due to the camera man focussing the lens on one individual such that nothing else would be seen on screen. In 58% (n = 120) of observations, the morays responded to head shaking by leaving their crevices, and the two fish then swam off through the reef (Video S2).
Joint movement was often interrupted, because moray eels could remain in a crevice for several minutes before moving on. Typically, a hunt ended unsuccessfully because prey escaped into a crevice that was inaccessible to the grouper.
In the majority of observations, the groupers either swam off immediately without further hunting attempts, or they remained nearby, usually above the hole but out of sight. This latter behavior usually lasted several minutes and sometimes led to a second hunt, presumably involving the same prey fish.
The dorsal fin was used as in the standard head-shake signal to the moray, but the head movements differed, most obviously because of the pauses between single shakes (Video S3). Headstand shakes invariably attracted other predators to the prey's location in the crevice.
On ten occasions, a moray eel joined the grouper and explored the crevices (Video S4). On five occasions, we observed moray eels catch prey when hunting with a grouper.
This is not surprising, however, as moray eels observed alone simply remained in their crevice and did not appear to search for prey. The individual fish that caught the prey swallowed it quickly and whole without any aggression from the unsuccessful partner.
We have presented several lines of evidence for interspecific communicative, coordinated, and cooperative hunting between two species of reef fish predators. We found the following: (1) individual groupers and moray eels frequently spent more time in association than predicted by a null model of chance encounters, (2) groupers actively signalled to elicit joint hunting and to recruit moray eels, (3) satiated groupers did not signal, and (4) both partner species increased their hunting success in association.
Although the evidence for groupers is straightforward, the typical nightly activity pattern of moray eels precluded any detailed statistical comparison of hunting success data. Thus, the outcome of joint hunting between the groupers and the moray eels appears to be a by-product mutualism .
Hence, interspecific coordinated hunting is linked to the well-known evolutionary problems of unequal payoffs and potential defection that are associated with altruistic behavior. Finally, phylogenetic constraints may limit the kind of roles that individuals are able to adopt, and so reduce the likelihood of successful coordinated hunting.
For example, a lioness will never be able to run with the speed of a cheetah, even though this ability would help in a coordinated hunt. Interspecific cooperation, as we have observed between groupers and morays, seems to overcome the difficulties of interspecific coordinated hunting.
Any potential cognitive constraints regarding the division of roles are absent, because associating partners behave in exactly the same manner as they do when hunting alone. Each player uses only its evolved hunting strategy, and there is no pressure to learn specific new behaviors that yield advantages when they form part of a coordinated effort.
Only a single West African population, in TAI National Park, Ivory Coast, is known engage in such behavior; all other chimpanzee populations hunt more opportunistically, following chance encounters with monkey prey . Such differences have generated great interest in the anthropological literature because of the disputed importance of complex cooperative hunting for early human evolution .
Our results suggest the latter, unless future studies are able to demonstrate more convincingly that complex cognitive processes underlie chimpanzee communication during hunt initiation. We hypothesize that swallowing prey whole, as we observed in the groupers and moray eels, is an important condition for the occurrence of interspecific cooperative hunting.
However, after successful hunts, competition would arise immediately over which species feeds first and which parts of the carcass are eaten, and problems of cheating and defection would be rife. Consequently, we propose that the defensibility of a kill is the decisive obstacle preventing the evolution of interspecific cooperative hunting in mammals and other taxa.
Moreover, we suggest that the multiple predation effect of interspecific cooperation is the key to overcoming the inherent problem presented by the joint hunting of unshakable prey; namely, overall prey capture rate needs to be at least twice that obtained by a solitary hunter in order to yield net benefits . We expect to find other species combinations that hunt cooperatively, but only in situations where there is no competition over carcasses.
All observations were made between September 2002 and December 2004 in the eastern part of Versa Areas, Ra's Mohammed National Park, Egypt. Along the 2800-m coastline, 14 groupers, varying between 55 and 100 cm in total length (estimation) were recognized by individual spot patterns on their body.
We do not know whether these results reflect natural encounter rates with groupers from a moray perspective or whether the data are biased due to the presence of humans. In brief, the model uses the average velocities of two groups or individuals in a 2-D space, plus a criterion for maximal distance, to calculate mean durations of associations .
Because we noted the movements of groupers only relative to the coastline, our calculation simplifies to a 1-D space, which yields lower swimming speeds and hence increases association durations predicted by the null hypothesis. The calculations further simplify because moray eels rarely, if ever, moved and can be assumed to be stationary objects.
The crucial determinant of association durations predicted by the null hypothesis is therefore the swimming speed of groupers relative to the coastline and our association criterion of 10 m. We constructed a map of the coastline and measured distances between key landscape points. This information combined with the duration of each protocol allowed us to calculate the average swimming speed of each grouper relative to the coastline.
The predicted mean association duration of the simplified model is the time it takes a grouper on average to swim 20 m, i.e., 100 s. To test the effects of feeding on grouper signalling, we allowed six individuals to eat a fish (purchased at the local market) at the onset of an observation session and then followed them for 120 min and recorded their behavior following our standard observational protocol.
We then compared these data with our recordings of the same individuals during observation sessions where we did not know their hunger state (matched pair design). This is because any analysis where the null hypothesis deviates from a 50:50 distribution (in our case it is roughly 10:90) is only useful if the number of observations is sufficiently high that predicted values for the rare situation is at least one unit.
We therefore analyzed all data together using a binomial test with a truncated expectation (10% of all successful hunts observed in association). Thus, groupers spend a large proportion of their time in association signalling to or waiting next to moray eels that did not leave their crevice.
We thank Dr. Mustafa Fonda and the Egyptian Environmental Affairs Agency for permission to work at Ra's Mohammed National Park, and the Park rangers, the Electrochemical Reef Construction (Econ) group of Essen University, and Ingo Riel for local support. Jürgen Chaucer greatly helped with data collection on moray eels and filming.
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In Chiba National Park, we have the pleasure of observing several species of moray eel, an incredible hunter with a flexible body to move between rocks and wait in crevices for passing prey, a keen sense of smell, and not just one but two sets of jaws. In the open ocean, Groupers are observed doing a sort of shimmying dance underwater to summon moray eels and signal their desire to hunt in a team.
More rarely, when an eel ignores the signal, some have even witnessed Groupers fearlessly approaching the moray and attempting to push it toward the target prey. This sort of cooperation is one of a few examples of different fish species teaming up underwater to hunt, and there are many other manners in which marine organisms partner up for the mutual benefit of both parties.
This sort of teamwork between the ocean’s many species goes to show how truly dynamic and complex life underwater can be, and how lucky we are to be witnessing some of this diversity here in Chiba National Park! Groupers feed by gulping down prey in the open water, while morays can pursue fish into hiding places in a reef.
Scientists are unsure whether cooperative hunting is an instinctive behavior for groupers and eels, or whether it is something they learn. Whatever the case, this unusual cooperation helps both kinds of fish boost their chances of catching a meal.
Coloration is yellowish, densely mottled with dark brown, with the front of the head purplish gray and the posterior margins of fins yellow-green. Most species lack pectoral and pelvic fins, adding to their snake-like appearance.
Their eyes are rather small; morays rely on their highly developed sense of smell, lying in wait to ambush prey. They possess large teeth, designed to tear flesh as opposed to holding or chewing.
When feeding, morays launch these jaws to grasp struggling prey and transport it into the throat and down to the rest of the digestive system. Moray eels are the only known type of animal that uses pharyngeal jaws to actively capture and restrain prey.