The Humphead wrasse is
naturally (biologically) vulnerable to fishing due to its characteristics of
long life and late sexual maturation (sexual maturation occurs at approximately
35-50 cm total length and up to 5 years of age, or more). These characteristics
mean that its life history is one that likely involves slow replacement (and
hence slow recovery from fishing) rates.
The Humphead wrasse spawns
in aggregations that can easily be targetted by fishers and hence are
particularly vulnerable to overfishing at the times and places at which
reproduction occurs. It has been well-documented that spawning aggregations in
several other reef fish species are particularly vulnerable to being overfished.
The Humphead wrasse can
change sex from female to male. This makes the species susceptible to
size-selective (=sex selective) fishing that could lead to imbalances in the
reproductive sex ratio and reduce reproductive potential.
Adult Humphead wrasse are
very vulnerable to night-fishing, especially if SCUBA is used, since they are
easily taken from the caves in which they sleep. Adults do not appear to be
particularly common anywhere in their geographic range (compared to
commercially taken fish in general) so that heavy nighttime fishing can quickly
reduce population numbers.
The species has a high
economic value and is a special favourite of both the live reef food fish trade
and with recreational divers. Because of its high value as food, it is heavily
sought by fishers and traders; as part of the luxury food fish market, its
value is likely to increase with rarity, so fishers will continue to fish this
species even as its numbers decline. On the other hand, its value to diving
tourism will remain high if animals are protected and remain alive in the wild.
The most preferred trade, or
market, size for this fish in the export trade as food is 'plate-sized' –
between about 30-60 cm (mainly 30-45 cm) total length. Plate-sized fish are
typically sexually immature since sexual maturity occurs at about 50 cm. This
means that large numbers of sexually immature fish are removed from the wild
for the live reef food fish trade. The relatively large sizes of these juvenile
fish mean that they would very likely survive to reproduce in the wild, if not
removed. If young fish are being removed before they can produce the next
generation, how can populations replace themselves and recover from fishing?
There is a heavy catch of
juveniles from the wild, not only for direct sale as plate-sized fish (see SIX
above) but also for so-called (and misnamed) 'mariculture' grow-out in which
these young wild fish are put into cages and grown-out until they attain
saleable size. This juvenile capture fishery is a type of activity that most
properly managed fisheries seek hard to avoid because of the negative effects
on the potential for future population recovery. Juveniles need to be protected
until they grow big enough to reproduce and replenish the population.
Full-cycle mariculture (i.e.
hatchery-based mariculture) is not yet possible for this species at commerical
levels and all fish are taken from the wild. Claims of full-cycle culture have
all been shown to involve the grow-out of young fish taken from the wild.
Cyanide is widely used to
catch this species, especially in parts of Indonesia and the Philippines, and
particularly for the juvenile (less than 50 cm) fish. Cyanide is often
introduced by the traders of live reef fish to fishing communities that do not
traditionally use this destructive fishing method. Cyanide is a poison and is
known to kill living coral. The Humphead wrasse, as with many other reef fish
and invertebrate species, depend on healthy coral reefs for shelter. Loss of
this habitat could severely affect reef communities, and their habitats.
Humphead wrasse fisheries
are typically unmanaged and, even if managed 'on paper', there is usually
little management or monitoring of Humphead wrasse in local fisheries.
Monitoring is urgently needed, both of local capture and of exports. Without
proper management and monitoring, it is impossible to know whether current
capture rates are sustainable or to establish safe quotas for the capture of
this vulnerable species.
