Groupers and Morays Hunting Together

A study published with the Public Library of Science (PLOS) Biology Journal notes some fascinating cooperative hunting behavior in the Red Sea:

Interspecific Communicative and Coordinated Hunting between Groupers and Giant Moray Eels in the Red Sea

Redouan Bshary, Andrea Hohner, Karim Ait-el-Djoudi, Hans Fricke

"Cooperative hunting, i.e., the increase in successful prey capture observed when two or more individuals engage in a hunt, has been demonstrated in a wide variety of species [1–4]. In many cooperatively hunting species, hunts can best be described as opportunistic, simultaneous individual hunts [4], in which each animal tries to maximise the probability of catching the prey for itself. True coordination, as defined in [5], exists only if individuals play different roles during a hunt. Role differentiation implies that individuals will adopt roles that have a lower probability of personal success or a higher risk of injury than other roles would offer, e.g., hunts where some individuals act as chasers while others block the escape routes of prey. Such coordination is known for only a handful of species [5–8], all of which are mammals or birds. Individual role specialisation within coordinated hunts is even more rare and has only been observed in two studies to date [7,8]. 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 [5]. The same population of chimpanzees is also well known for respecting prey ownership, where the successful individual shares with cohunters [5]. While simultaneous feeding on a prey carcass may also occur in carnivores, access in these species is best predicted by individual rank and/or nepotistic toleration of related lower ranking individuals [4].
"Here we describe interspecific and communicative hunting between the grouper, Plectropomus pessuliferus, and the giant moray eel, Gymnothorax javanicus, 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. The hunting strategies of the two predators are also very different. Groupers are semi-benthic piscivors, which hunt in open water. 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. The hunting strategies of the two predators are therefore complementary, and a coordinated hunt between individuals of the two species confronts prey with a multipredator attack that is difficult to avoid [9]; prey are not safe in open water because of the grouper hunting strategy but cannot hide in crevices because of the moray's mode of attack.
"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 Waser's gas model [10] 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. We then discuss the selective conditions that might promote such an unusual interspecific cooperation."