Moray Eels


Green Moray closeup

 

When I began diving in 2007, I had some preconceived notions about certain ocean critters.

Sharks are out to eat as many humans as they can. Eels would attack you if they happened upon you and possibly swallow you whole! Octopus would wrap you up in their arms and drag you into their lairs to eat you slowly, one.bite.at.a.time!!!

Over the years I have had some very up close and personal encounters with all three of these critters and they have become some of my most treasured creature encounters of my life!

I have discovered through observation that these top 3 “scary creatures” are either completely uninterested in what humans are doing or curious enough about us to observe and interact with us. While I am sure that there are some dangerous individuals out there, there are many more dangerous human divers out there! Our impact on these creatures far outweighs their impact on us.

But I digress.

This article is about one of my favourite ocean creatures, eels. so please read on and hopefully if you have any preconceived prejudices about this amazing creature, you will look at them in a different light, the next time you are lucky enough to encounter one on a dive!

Morays are frequently thought of as particularly vicious or ill-tempered animals. In truth, morays hide from humans in crevices and would rather flee than fight. They are shy and secretive, and attack humans only in self-defense or mistaken identity. Most attacks stem from disruption of a moray’s burrow (to which they do react strongly), but an increasing number also occur during hand feeding of morays by divers, an activity often used by dive companies to attract tourists. Morays have poor vision and rely mostly on their acute sense of smell, making distinguishing between fingers and held food difficult; numerous divers have lost fingers while attempting hand feedings, so the hand feeding of moray eels has been banned in some locations, including the Great Barrier Reef. The moray’s rear-hooked teeth and primitive but strong bite mechanism also makes bites on humans more severe, as the eel cannot release its grip, even in death, and must be manually pried off. While the majority are not believed to be venomous, circumstantial evidence suggests a few species may be.

Moray eels’ habit of keeping their mouth open is sometimes misinterpreted as a threatening posture. In reality, this is how they breathe. They extract the oxygen from the water as it flows through their mouth and out their siphon.

Moray eels are cosmopolitan, found in both tropical and temperate seas, although the largest species richness is at reefs in warm oceans. Very few species occur outside the tropics or subtropics, and the ones that do only extend marginally beyond these regions. They live at depths to several hundred meters, where they spend most of their time concealed inside crevices and alcoves.

Moray eels’ heads are too narrow to create the low pressure most fishes use to swallow prey. However, they have a second set of jaws in their throat called pharyngeal jaws, which also possess teeth (like tilapia). When feeding, morays launch these jaws into the mouth, where they grasp prey and transport it into the throat and digestive system. Moray eels are the only animals that use pharyngeal jaws to actively capture and restrain prey.

1024px-Pharyngeal_jaws_of_moray_eels.svgBy Zina Deretsky, National Science Foundation (after Rita Mehta, UC Davis); Ryan Wilson (pbroks13)

 

 

Morays secrete a protective mucus over their smooth, scale less skin, which in some species contains a toxin. They have much thicker skin and high densities of goblet cells in the epidermis that allows mucus to be produced at a higher rate than in other eel species. This allows sand granules to adhere to the sides of their burrows in sand-dwelling morays, thus making the walls of the burrow more permanent due to the glycosylation of mucins in mucus. Their small, circular gills, located on the flanks far posterior to the mouth, require the moray to maintain a gap to facilitate respiration.

Morays are carnivorous and feed primarily on smaller fish, octopuses, squid, cuttlefish, and crustaceans. Groupers, barracudas and sea snakes are among their few predators. Commercial fisheries exist for several species, but some cause ciguatera fish poisoning.

Reef-associated roving coral groupers have been observed to recruit giant morays to join them in hunting for food. The invitation to hunt is initiated by head-shaking. The rationale for this joining of forces is the ability of the morays to enter narrow crevices and flush prey from niches not accessible to groupers. This is the only known instance of inter-species cooperative hunting among fish. Cooperation on other levels, such as at cleaning stations, is well known.

Now, time to go dive! Meet new critters like the Moray Eel and appreciate them for the amazing creatures that they are and enjoy your encounter!