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planktonic prey and share other common traits such as
longevity, late maturation and low reproductive rates.
These characteristics, combined with predictable
surface-swimming behavior while feeding, have made
rays particularly vulnerable to overexploitation. They
generally produce a single pup after a 12-month
gestation, and there may be up to five years between
gestations in some species. Their brains are large
relative to their body size (the largest of all sharks
and rays), which implies that they are as smart as an
intelligent and sociable bird, a fact that won’t surprise
anyone who has had a protracted encounter with a
manta. Their behavior is a key driver of the growing
manta tourism industry, which generates an estimated
$73 million in direct revenue annually.
Differences in the habitat preferences and life cycles
of these migratory rays expose them to different but
overlapping threats. Coastal mantas (
M. alfredi
) and
some mobulas are threatened by small-scale artisanal
fisheries that use nets and harpoons in countries
such as Indonesia and Mozambique; oceanic mantas
(
M. birostris
) and other mobula species are further
threatened by pelagic tuna purse-seine fisheries.
Fisheries that target mantas intentionally seek not the
animal’s meat but rather its breathing apparatus — the
gill plates, which are dried and sold in Asia for their
supposed medicinal properties.
Studies estimate that the mortality of mobulas
captured and released from tuna purse-seine nets is
close to 100 percent. Reducing the threat of purse-
seine capture has been tackled by the Western and
Central Pacific Fisheries Commission (WCPFC), which
in 2015 proposed procedures for rapid and careful
release of the animals from the nets. These measures
have not yet been widely implemented, and the
common practice of gaff-hooking rays caught in the
nets further contributes to purse-seine mortality.
Several countries, including Mexico, Indonesia, Peru,
Australia, Ecuador, Maldives, Seychelles and Yap, have
now enacted legislation to protect mantas, in light of
dramatic declines in their numbers following the growth
of fisheries that target them. Yet the gulf between
legislation and actual implementation of protective
measures is wide. Unsustainable fishing of mantas
continues, even in countries that have protections in place.
Additional measures to reduce threats from fisheries
and trade have been recently implemented through two
key international agreements: the Convention on the
Conservation of Migratory Species of Wild Animals
(CMS) and the Convention on International Trade in
Endangered Species of Wild Fauna and Flora (CITES).
CMS Appendix I requires parties to the treaty
to protect CMS-listed species in their country,
while the complementary Appendix II encourages
range states — countries through which migratory
species pass — to collaborate internationally for the
conservation and management of species. An example
of such collaboration is the 2010 Memorandum
of Understanding (MOU) on the Conservation of
Migratory Sharks, which originally listed a small number
of shark species in its Annex 1. In 2011, the oceanic
manta was listed in both CMS appendices. This listing
was followed in 2014 by the addition of the coastal manta
and all nine mobulas, partly in acknowledgement that
the similar appearance of unprotected devil rays could
thwart protection of the giant mantas. In February 2016,
participants at the Second Meeting of the Signatories
to the MOU on the Conservation of Migratory Sharks
added all species of mantas and mobulas (and some more
sharks) to Annex 1 and adopted a revised conservation
plan (Annex 3) for 2016-18 that will improve our
knowledge of both the species and the fisheries.
CITES prohibits commercial trade in species listed
in its Appendix I (most endangered), establishes
processes for ensuring that trade in its Appendix II
species is sustainable and has the capacity to impose
sanctions if parties fail to comply. CITES listed all
mantas in Appendix II in 2013, recognizing that
fisheries driven by international demand for gill plates
caused stock depletion. CITES Appendix II requires
exporting countries to confirm that exports of listed
species were obtained legally (e.g., not taken from
protected areas or using illegal fishing gear) and that
the harvest from the wild population was sustainable,
among other things. In September 2016, parties will
debate adding all the mobulas to CITES Appendix II,
partly because some species face the same threats and
also because of “lookalike” issues, which can undermine
the protection of the most threatened species if their
products (i.e., gill plates) cannot be differentiated.
These international conservation measures are timely,
providing hope that it will be possible to reverse declines
in several known manta/mobula fisheries and mitigate
threats from other not-yet-fully-described fisheries.
Furthermore, the International Union for Conservation of
Nature (IUCN) Global Devil and Manta Ray Conservation
Strategy, developed by manta experts in Durban, South
Africa, in 2014, will soon be released to guide research
and conservation priorities and drive future conservation
and collaborative efforts for all devil rays.
The considerable advances made worldwide in the
research and conservation of mantas and mobulas are
encouraging. It is clear that we are finally beginning to
show much deserved sympathy to these devils of the
sea. This is no time for resting on laurels, however; we
need to move faster and more efficiently to mitigate
the multiple threats to these magnificent marine icons
so their populations may thrive once again.
AD
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