Description

The Humphead Maori Wrasse is one of the largest coral fish in the world. Its total length (TL) ranges from 2-3cm in juveniles to 250cm in adult fishes (just abit longer than the world’s tallest basketball player). An adult wrasse can weigh up to 191kg (almost as heavy as a sumo wrestler!!).  Male Humphead maori wrasses are on average 1.4 times larger than the females who can only grow to a maximum of 100cm TL. Adult Humphead maori wrasses can be easily distinguished from other fishes by the prominent bulbous hump on the forehead. This bulbous hump is not so obvious in juveniles. This fish has a characteristic feature that easily distinguishes it from other fishes usually sold at the fish markets in Fiji: the eyes are relatively small and two black lines run backward from each eye, with two more slanting obliquely forward toward the upper lip. Juvenile wrasses are of a different colour and morphology (reduced hump on the forehead, small size) to adults, and consequently are thought to be a different fish by fishermen and have different common (English and Fijian) names as they grow (see following page for images of the various sizes). For a closer look at the size of this fish, go to http://www.humpheadwrasse.info/.

Distribution

Humphead wrasses are widely distributed on coral reefs and inshore habitats of the tropical Indo-pacific region (from western Indian Ocean and Red sea to southern New Caledonia and into the central Pacific Ocean), including Fiji waters.

Habitat Ecology and Behaviour

Different life stages are associated with different parts of the marine ecosystem. Juveniles are usually associated with inshore reef habitats (sea grass beds, mangroves areas, coral rich areas of lagoons); while adults are more common offshore in deeper waters. Adult Humphead maori wrasses have a strong association with well developed coral reefs and lagoons. Humphead maori wrasses, unlike most other fishes, cannot settle on the sand to rest, preferring large crevices of the vertical face of coral reefs.

Female humphead maori wrasses outlive males, and can live up to 32 years. This fish reaches sexual maturity when it is about eight years old and 40-60cm in total length. Some individuals undergo sex reversal (from female to male) at around 15 years of age. They feed on mollusks, starfishes, sea urchins, crustaceans and several other marine invertebrates. Humphead maori wrasses are probably also one of the few predators of the toxic crown of thorns starfish (Acanthaster planci). Humphead maori wrasses are usually solitary but have been observed in pairs and aggregate during spawning time.

Threats

Humphead maori wrasses grow slowly, mature late and naturally occur in low numbers. Advanced and illegal fishing methods (night fishing on compressed air, cyanide, bomb fishing), capture of juveniles (because of the colour and morphological variation between juveniles and adults, juveniles are still harvested by local fishermen who are unaware that it is the same fish) and increased harvesting pressure (for the live reef food fish trade in South East Asia) have added to its scarcity and vulnerability. Humphead maori wrasses are most vulnerable at spawning time, which is when they aggregate. Fiji is one of the identified spawning sites for this fish. Harvesting of adults at spawning time, harvesting of juveniles (contributes to poor recruitment, reproduction and regeneration), continued trade and continued habitat (coral reef) destruction remains a threat to the survival of this species in Fiji. The habitat choice in Humphead wrasses also adds to its risk to captivity. This fish is one of the first fish species to retire at night, and rests in crevices on the face of coral reefs, making it an easy prey for night fishermen. Because of its huge size and difficulty in catching this fish, some fishermen have been known to squirt the highly toxic sodium cyanide on wounded or sleeping wrasses. Sodium cyanide is a poison that not only kills the fish but also every other living organism in the area. The overall reef ecosystem is thus destroyed and made non productive for the following years.

Conservation Status

Even though the Humphead maori wrasse is widely distributed, all country based reports on this fish have shown severe declines in the wild population, even in its most suitable habitat. In Fiji, annual catch decreased by more than 80%, with catch rates of 2-5 large fish per month in the 1970s and 1980s declining to just 1 per month in 2003. Humphead maori wrasses are suspected to be extirpated from one of the Lauan islands because of over-fishing. Even though this fish is included in the CITES Appendix II it is still being harvested for trade and illegally sold at the Fiji fish markets.  For more information on this fish, go to http://www.humpheadwrasse.info/.

Remarks and Cultural Significance

Even though the Humphead maori wrasse is widely distributed, all country based reports on this fish have shown severe declines in the wild population, even in its most suitable habitat. In Fiji, annual catch decreased by more than 80%, with catch rates of 2-5 large fish per month in the 1970s and 1980s declining to just 1 per month in 2003. Humphead maori wrasses are suspected to be extirpated from one of the Lauan islands because of over-fishing. Even though this fish is included in the CITES Appendix II it is still being harvested for trade and illegally sold at the Fiji fish markets.  For more information on this fish, go to http://www.humpheadwrasse.info/.

References

Grignon, J (personal communication);
IUCN (2006);
Russel (2004);
Sadovy et al. (2004);
Scales et al. (2007);
Thaman (1998);
Thaman, B (personal communication);
Yeeting et al. (2001).

Front Page Photo: Baravi Thaman