Life Cycle of the Humphead
Wrasse – a short primer
The Humphead wrasse changes
markedly in both body form and colouration throughout its lifetime. It occurs
widely in the Indo-Pacific, in coastal waters from inshore down to about 100 m.
It is found from the Red Sea and African coast, across the Indian Ocean and
much of the Pacific, north to southern Japan and the coast of southern China,
and south to New Caledonia.
Juveniles occur in coral-rich
areas of lagoon reefs, particularly among live thickets of staghorn Acropora
sp. corals, in seagrass beds, murky outer river areas with patch reefs, shallow
sandy areas adjacent to coral reef lagoons and in mangrove and seagrass areas
inshore. They tend to move into somewhat deeper waters as they grow older
and larger. Juveniles are all, by definition, sexually immature. It takes
quite a long time, possibly up to 5 years, with the fish reaching about 35-50 cm in total
length, before individuals attain sexual maturation.
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Adults are more common offshore than inshore, their
preferred habitat being steep outer reef slopes, reef drop-offs, passes and
tops, channel slopes, and lagoon reefs to at least 100 m. They are typically
found in association with well-developed coral reefs and may be somewhat
sedentary; the same individuals may be seen along the same stretch of reef for
extended periods. Indeed, many
commercial dive sites have their ‘resident’ Humphead wrasse, a favourite
species for divers in many areas.
Population densities are
evidently never high, even in preferred habitats. For example, in unfished or
lightly fished areas, adult fish densities may range from 2 to 20 (but rarely
>10) individuals per 10,000 m2 of reef. This is very low for a
commercially targeted reef species and is more akin to densities of large
terrestrial animals. In heavily fished areas, the numbers can drop to at least
ten times less than in unfished areas. In some countries the species has become
rare due to overfishing.
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Humphead wrasse feed
primarily on molluscs and on a wide variety of invertebrates including crustaceans
and echinoderms; heavy shells are crushed with the tough pharyngeal teeth and
the species also take fishes. It appears to be one of the few predators of
toxic animals such as the crown of thorns starfish, boxfishes and sea hares.
Maximum sizes recorded for
this species are from Queensland at 2.29 m and 190.5 kg, and 2.5 m and 191 kg.
In general, however, fish much larger than 1.5 m are rarely recorded. The
reason(s) for this is (are) not clear but it is possible that larger fish are
naturally rare, appear to be rare because they are wary, have become rare or
occur predominantly in waters deeper than those typically visited by divers, or
fished.
The Humphead wrasse can live
for at least 3 decades. Unpublished age and growth studies using the sagittal otoliths
(ear stones) and length data suggest a longevity of at least 32 years for
females and 25 for males, if the growth checks in otoliths are deposited
annually. On the Great Barrier Reef of Australia, fish attain about 1 metre in
total length in about 28 years and sexual maturity in about 5 years. Nothing is
known of the natural mortality of the Humphead wrasse. The longevity of the
species, however, and our limited knowledge of reef fish biology, in general,
suggest that adult mortality is low. It is likely, following the early
post-settlement period typically associated with high mortality levels in
fishes, that natural mortality drops rapidly after fish settle out from the
plankton.
This species spawns
(reproduces) in pairs formed within larger social groups that form temporary aggregations. Sometimes spawning
aggregations can number several hundred fish in unexploited areas; at other
times mating groups are much smaller. Planktonic eggs are released into the
water column and drift away from the spawning site. After hatching, the larvae
stay in the water until they settle on the substrate. Population sizes and
structures are not yet known for this species.
This wrasse is interesting
because some individuals change their sex. Adult females are known to change to
adult males, a form of sequential hermaphroditism that is found not only in
wrasses but in many reef fishes. We do not yet know what controls the timing of
sex change, or how ‘decisions’ are made about which fish change sex. Indeed, we
still have much to learn about the biology of this species.
For additional information
and photos see:
http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=5604&genusname=Cheilinus&speciesname=undulatus
(Information extracted from: The humphead wrasse, Cheilinus undulatus: synopsis of a threatened and poorly known giant coral reef fish by
Sadovy, Y, Kulbicki M., Labrosse P., Letourneur Y., Lokani, P., and T. J.
Donaldson in Reviews in Fish Biology and Fisheries 13(3):327-364)