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The
effects of disturbances according to the type of atoll
The fish communities inhabiting
the atolls undergo disturbances of all kinds, which are
caused by both human and natural agents. The main
disturbances for which humans are responsible are
fishing activities, but other activities such as opening
a passage in the barrier reef, pearl farming and
collecting material for building purposes can also have
disturbing effects. Some of the most harmful natural
disturbances are obviously the cyclones, but there are
also some rare but significantly harmful processes at
work, such as those which have caused the eutrophisation
of the Hikueru lagoon.
Small
atolls and minor production
Most of the fish sold on the
fish markets or caught for subsistence purposes have the
following biological characteristics: they are
long-lived, they have relatively slow growth rates, at
least after reaching the first reproductive phase, and
they have a relatively low rate of natural recruitment.
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Consequently, the fish
communities inhabiting the atoll lagoons do not
withstand the onslaughts of fishing. This is all
the more so in the case of the smaller atolls |
Since,
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these atolls are inhabited by
fewer large-sized species (fig) |
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there are lower usable
biomasses available (fig16). De
nombreuses espèces ne sont pas exploitables
par goût ou tradition, du fait de leur petite
taille ou par risque de ciguatoxicité... mais l ’importance
des seules espèces commerciales augmente avec
la taille des lagons. |
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Pelagic species and benthic
species
Table
4: average values biomasses of the main commercial
fishes for small or medium lagoons of atolls,
having a low exploitation
The
most intensively fished species (Tab4)
are the pelagic fish (caranx and some types of Naso
spp.), which generally resist the pressure exerted
by fishing better than the benthic species (such as sea
loaches and sturgeons), although some benthic species (such
as parrot fish and mullet) are probably able to
withstand quite heavy fishing pressures.
Change
of sex
It
is also worth noting that the members of many species
can make a change of sex upon reaching a certain size,
and that fishing selectively for large individuals can
have detrimental effects on the sex-ratio, to the extent
that it can affect these species’ reproductive
capacities.
Stability
of the big-size atolls
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Although
it is not yet possible to reach any definite
conclusions, it does seem likely that the larger
atolls are inhabited by more stable communities
than the smaller ones. See
figure
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Withstanding
to a short-time severe disturbance
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The atolls will also probably
recover more easily from a severe but
short-lasting disturbance than from a weaker but
more long-lasting one. This is due to the
pattern of production on the atolls. |
A
severe disturbance will weaken some functional groups,
such as those whose vital strategies are based on
relatively short life-spans and high rates of
recruitment. These groups generally recover quite fast
via a process of allogenic recruitment. If the
disturbance persists, however, the functional groups
containing species whose vital strategies are based on
long life-spans and late reproductive efforts or low
recruitment rates will be weakened.
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The
resulting long-term weakening of a "functional
group" will affect the fauna and the
benthic flora and thus considerably damage the
ecosystem as a whole. |
References Kulbicki
M;, Galzin R., Harmelin-Vivien M., Mou Tham G., Andréfouët
S. 2000 Les communautés de poissons lagonaires dans les
atolls des Tuamotu, principaux résultats du programme
TYPATOLL (1995-1996). Nouméa, IRD, Doc.Sci. Tech. II3:
26-125
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