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Diving with Moray Eels

Take a Foray into the World of Morays

The breathing gape of a giant moray eel can make it look quite fiersome

You are finning along a reef with fish swimming all around you when suddenly something makes you stop on your tracks. You see a sight that at once captivates you and implores you to fix your gaze on a head protruding from a hole, seemingly glaring out and opening and closing its jaws in an apparently menacing fashion. You have just spotted a moray eel!

So are they dangerous predators, better to be given a wide berth? If not then why do they seem to adopt such an aggressive appearance? What are the 'dos' and 'don'ts' of diving with moray eels? Let us take a closer look at this popular reef creature and see what makes the moray so interesting.

Moray Eel Fact Sheet

Family name: Muraenidae
Order name: Anguilliformes
Common name: Moray eel
Scientific name: Muraena

Distinguishing Features

Moray eels vary considerably in size depending on species, from the ribbon moray at around 25 cm to the giant moray which can be as much as 4 metres in length. Similarly, skin diversity and colour has as many variations as there are species. You can see morays with skin that is speckled, striped, freckled or tattooed, and coloured in a variety of hues including brown, green, off white, yellow, black and blue.

Despite all of these variations it is normally pretty easy to tell when you are looking at a moray eel since their similarities are such that they are not often confused with other marine creatures. Moral eels have a dorsal fin which runs almost the entire length of the body, from the head to the caudal and anal fins, and are made to appear like a snake by their absence of pectoral and pelvic fins.

The head of the moray eel is large with small eyes located quite far forward, and a wide mouth with large teeth for tearing flesh rather than grinding or holding in place. They have a secondary set or toothed jaws in their throat called pharyngeal jaws, which are thrust forward to grab and drag prey down through their digestive system. They are the only known creature to use pharyngeal jaws to grab and hold prey.

There are more than 100 species of moray eel, including the honeycomb (Muraena melanotis), giant moray eel (Gymnothorax javanicus), zebra morays (Gymnomuraena zebra), snowflake morays (Echidna nebulosa), and white eyed moray (Siderea thyrsoidea), Fimbriated moray (Gymnothorax fimbriatus) and the Ribbon eel (Rhinomuraena quaesita).

Behaviour

A ribbon eel is a species of moray

Moray eels secrete a mucus over their smooth skins in greater quantities than other eels, allowing them to swim fast around the reef without fear of abrasion. Also sand-dwelling morays can make their burrow stronger and permanent, as granules adhere with the mucus and attach to the sides of the burrows. There are often parasites on the surface of the moray eel's skin making them popular with cleaner shrimp and cleaner wrasses.

Due to the small size of the gills, morays have to continuously open and close their mouths in a gaping fashion to maintain a flow of water and facilitate respiration. This is often mistaken as aggressive posturing by the unaware and is part of the reason for the moray eel's fearsome reputation. Another may be their inability, due to poor eye sight, to distinguish where food ends and where human fingers begin. As well as attacking when under threat, moray eels have been known to bite off and swallow digits of those feeding them.

Feeding Habits

Moray eels are carnivores and their diet consists mainly of other fish or cephalopods, as well as mollusks and crustaceans. They go hunting mostly at night and their chief hunting tool is their excellent sense of smell which makes up for their poor eyesight. This means that weakened or dead creatures tend to be easy to detect and are therefore the moray eel's favoured food.

Otherwise they hide in their crevices waiting until their prey is close enough, and then they launch themselves from the burrow and clasp the prey with their powerful jaws. Their lightning fast strikes are devastatingly impressive, as diver that has seen a moray eel attack will verify.

Reproduction

Scientific studies have shown hermaproditism in morays, some being sequential (they are male, later becoming female) and others are synchronous (having both functional testes and ovaries at the same time) and can reproduce with either sex.

Courtship among compatible morays begins when water temperatures reach their highest, and they begin sexual posturing in the form of gaping widely. Then the morays will wrap each others' long slender bodies together, either as a couple or 2 males and a female. They simultaneously release sperm and eggs in the act of fertilisation, which signals the end of their relationship.

Life Cycle

On hatching, the eggs take the form of leptocephalus larvae, which look like thin leaf-shaped objects, that float in the open ocean for around 8 months. Then they swim down as elvers to begin life on the reef and eventually become a moray eel, living between 6 and 36 years depending on species in a natural life cycle.

Predation

Cleaner wrasse at work on a honeycomb moray's teeth  - photo coutesy of ScubaZoo

The main predators of moray eels are other moray eels but also large groupers, barracudas and people. In truth this represents very few predators, which explains why they have the confidence to live in burrows or crevices in the reef from which swift flight maybe difficult.

Distribution and Habitat

Morays are found worldwide in tropical and temperate seas, particularly in relatively shallow water among reefs and rocks, as well as in estuarine areas.

Ecological Considerations

Morays are fished, but are not considered endangered. This is due in no small part to their toxicity. Ciguatoxin, the main toxin of ciguatera, is produced by a toxic dinoflagellate and accumulated up through the food chain, of which moray eels are top, making them dangerous for humans to eat. This fact was apparently the cause of death for King Henry I of England, who expired shortly after feasting on a moray eel.

Dive Sites

There are many great destinations for diving in the presence of these fascinating creatures, with some of the best being:

The Americas

  • Ambergris Caye, Belize • Cocos Island in Costa Rica
  • Galapagos Islands, Ecuador • Sea of Cortez, Mexico

Australia

  • Cairns • Osprey Reef
  • Ribbon Reefs

Fiji

  • Taveuni Island • Viti Levu

Indonesia

  • Ambon • Bali
  • Banda Islands • Bunaken - Manado
  • Cenderawasih Bay • Lembeh Strait

The Maldives

  • Ari Atoll • North Male Atoll
  • South Male Atoll • Far North Atolls

Malaysia

  • Mabul Island

Myanmar - Burma

  • Mergui Archipelago

Red Sea

  • Hurghada • Sinai Peninsula

Thailand

  • Khao Lak • Krabi
  • Phi Phi Islands • Phuket
  • Richelieu Rock • Samui Island
  • Similans

Dive The World Recommendations: the Maldives, Phuket in Thailand, Ambon in Indonesia, and Burma.


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