A moray eel is watching you from a hole in the reef, mouth opening and closing. Every diver reads that as a warning. It is the animal breathing. Morays have small gill openings and have to pump water through the mouth to move it over the gills, so the gape you were taught to find menacing is an eel doing nothing at all.
Most of what divers believe about morays works like that: a fair guess from the outside that the biology contradicts. They are not aggressive toward divers, and they are not interested in eating one. What they actually do is stranger than the reputation, and two pieces of it were only published in the last twenty years.
What morays actually do
A second set of jaws
Moray eels solve a feeding problem in a way no other fish does. When a moray grabs prey, a second set of jaws launches from its throat into the mouth, clamps onto the fish and drags it backwards to be swallowed. Rita Mehta and Peter Wainwright published the mechanism in Nature in 2007, and it is still the only described case in a vertebrate of a second jaw apparatus that both holds prey and moves it. Every other fish on the reef swallows by suction and momentum.
The mechanism explains the temperament. It works on small reef fish and invertebrates, and it is built for ambush in a confined space rather than pursuit in open water. A moray is a crevice specialist, not a rover, which is why nothing about it is designed to take on something the size of a diver.
They hunt with groupers
The second thing happens out on the reef. From the Red Sea to the Indo-Pacific, roving coral groupers hunt in open water and recruit giant morays out of the reef to work with them. The grouper finds a moray, swims up close and shakes its head rapidly in front of the eel’s face. The moray reads it as an invitation, leaves the reef and hunts alongside. Fish flushed out of the coral by one become available to the other, and both eat better than they would alone.
Redouan Bshary and colleagues documented it in the Red Sea in PLoS Biology in 2006, and it has since been recorded across the Indo-Pacific, Indonesian reefs included. The grouper signals when it is hungry, and the behavior is learned rather than instinctive. This is not an animal that treats a diver as a competitor or a meal.
Are moray eels dangerous to divers?
Moray bites are uncommon in recreational diving. Riordan and colleagues reviewed moray attacks in Wilderness and Environmental Medicine in 2004, and Barreiros and Haddad reported the same pattern in the Journal of Venomous Animals and Toxins in 2008: the injuries are infrequent, they turn up all over the world, and the people getting hurt are mostly fishermen handling hooked or netted eels rather than divers.
The bites that do happen on dives follow a pattern. Someone reaches into a crevice without looking. Someone corners an animal to photograph it. Someone hand-feeds one. In every case the eel is defending itself, not hunting.
That said, a moray bite is a serious wound. The teeth angle backwards and tear rather than puncture, and infection from reef bacteria is the real danger. If you are bitten, get out of the water, irrigate the wound thoroughly and see a doctor about antibiotics. Treat it with the urgency you would give a deep coral laceration.
Which species you will meet
| Species | Scientific name | Size |
|---|---|---|
| Giant moray | Gymnothorax javanicus | Up to 3 m |
| Ribbon eel | Rhinomuraena quaesita | Around 1 m |
| Snowflake moray | Echidna nebulosa | 75 cm |
| Fimbriated moray | Gymnothorax fimbriatus | 80 cm |
| Whitemouth moray | Gymnothorax meleagris | 1 m |
The ribbon eel is the odd one on that list. It is a protandrous hermaphrodite: it matures as a male and can later become female, and the color tracks the change. Juveniles are black with a yellow dorsal fin. Functional males are electric blue with a yellow snout. Functional females are yellow.
Worth knowing before you go looking: the yellow female phase is rarely seen by divers, and much of what is known about the full sex change comes from animals in captivity. In the water you will almost certainly meet black and blue animals, and it is easy to log them as two different species when they are one animal at two points in its life.
Where to find them
Morays live anywhere there is structure. Some sites are more reliable than others.
Bali: Blue Lagoon and the USAT Liberty
Blue Lagoon at Padangbai in east Bali is one of Indonesia’s most consistent ribbon eel sites. The drop-off starts at 8 meters and the ribbons sit in the shallower sections of the wall, so this is a shallow hunt rather than a deep one. Morning dives are the most productive.
The USAT Liberty wreck at Tulamben is a US Army cargo ship that a Japanese submarine torpedoed in 1942. It was beached at Tulamben for salvage and stayed there until Mount Agung’s 1963 eruption pushed it into the water, which is how it became the dive site it is now. It lies on a black sand slope in northeast Bali at depths from 5 to 30 meters, and giant morays are permanent residents in the hull sections. The shore entry and the shallow end make it one of the easiest places in Indonesia to spend unhurried time with a large eel, and it rewards anyone who moves slowly and looks into structure. It is on our list of the best dive sites in Bali for reasons that go well beyond the morays.
Sulawesi, Raja Ampat and Alor
Old Port in Gorontalo is a muck site where sand and scattered rubble make ideal habitat for small, cryptic eels. It works best at slack tide and produces snowflake and fimbriated morays regularly. Night dives here are good for ribbon eels out hunting.
Raja Ampat holds the highest reef fish diversity recorded anywhere, according to the surveys behind Conservation International’s Bird’s Head Seascape program. Morays are part of that count, and dense hard coral at every depth gives them endless structure to occupy. A five to seven day liveaboard will turn up several species without anyone going looking.
Alor has steep topography, current-driven walls and the cooler upwelling water the region is known for. The depth profiles and the structure produce consistent moray sightings on most reef dives.
How to dive safely around them
- Keep your hands out of holes and crevices. A moray in its hole cannot flee. Your hand in the entrance leaves it nothing to do but defend itself. This one rule prevents nearly every bite.
- Hold your buoyancy and stay off the reef. Bracing on a ledge to steady a camera is how divers put a hand somewhere they never looked.
- Never hand-feed eels. Fed morays lose their caution and start approaching divers, and some have injured the person holding the food. Responsible operators in Indonesia ban it outright.
- Give an eel room. A moray crossing open reef is traveling, not attacking. Stop, stay low and let it go.
- Take more care at night. Morays hunt after dark. Keep your torch beam off their head and keep your distance, because an eel interrupted mid-hunt can be defensive.
Plan your dive
Ocean Earth Travels runs diving in Bali, Sulawesi, Raja Ampat and Alor, on day boats and liveaboards, at every experience level. If you want to see moray eels we can tell you where and when. If you do not care about morays but want to read the reef better, knowing that the grouper and the eye in the hole are hunting partners changes what you watch on every dive. Either way we build the itinerary around what you actually want to see.
Tell us your dates and the destinations you have in mind and we will put a plan together.
Frequently asked questions
Moray bites are uncommon in recreational diving. The medical literature describes them as an infrequent problem that mainly affects fishermen handling hooked or netted eels. Bites on divers are defensive and follow a pattern: a hand pushed into a crevice, an animal cornered for a photograph, or hand-feeding.
They are breathing. Morays have small gill openings and pump water over the gills by opening and closing the mouth. It is not a threat display.
Yes. Morays have pharyngeal jaws in the throat that launch forward into the mouth, grip the prey and drag it back to be swallowed. Mehta and Wainwright published the mechanism in Nature in 2007.
Yes. Coral groupers recruit giant morays by swimming up to them and shaking their head in front of the eel’s face. The moray leaves the reef and hunts alongside the grouper, and fish flushed by one become available to the other. Bshary and colleagues documented it in the Red Sea in PLoS Biology in 2006, and it has since been recorded across the Indo-Pacific.
Ribbon eels are protandrous hermaphrodites, which means they mature as males and can later become female, and the color tracks that change. Juveniles are black with a yellow dorsal fin, functional males are blue with a yellow snout, and functional females are yellow. The yellow female phase is rarely seen by divers, so in practice you will meet black and blue animals.
Blue Lagoon at Padangbai and the USAT Liberty wreck at Tulamben in Bali are the most reliable sites for ribbon eels and giants. Old Port in Gorontalo is consistent for the smaller muck species. Raja Ampat and Alor both produce morays on most reef dives.
