Appendix II listing for silky, thresher sharks

Silky shark declines are primarily due to overexploitation by fisheries supplying fin products for international trade.For centuries, 1,150 species of Elasmobranchs (510 sharks and 650 rays) have been utilized for their flesh, oil, and skin. Recently, however, the demand from Asia for shark fin has led to a crisis of exploitation.

Many Elasmobranch species have been recognized as being vulnerable to overfishing due to their life–history characteristics such as slow growth, late maturity, long gestation periods and limited number of pups.

Some species populations declined by as much as 90 percent because of this increased fishing pressure.

Because many of these species are considered apex predators, the decline could have far-reaching consequences for the ecosystems.

Two types of sharks are proposed to be added to the second appendix of CITES next month: silky sharks and thresher sharks.

Despite their significant role, Elasmobranchs remain poorly understood, and scientific research is sorely needed. Here is what we do know about them:

Silky sharks, Carcharhinus falciformis, have slender bodies and smoother skin. They have dark grey to bronze coloration dorsally and white ventrally, and are characterized by the presence of an interdorsal ridge. Their average length is 1.8-2.3m, and the maximum length could reach 3.5m.

READ: IFAW CITES Briefing Sheet - Sharks – 2016

Silky sharks are oceanic and coastal sharks found near the edge of continental shelves and out in the open ocean, outside the exclusive economic zones (EEZs) of coastal States. (An EEZ is a sea zone prescribed by the United Nations Convention on the Law of the Sea over which a state has special rights regarding the exploration and use of marine resources.) Silky sharks are a high trophic level predator in ocean ecosystems feeding mainly on teleosts (bony fish) and cephalopods (squids and octopus).

The greatest threat to the silky shark is fisheries mortality. Victim of both utilized bycatch and discarded bycatch species, C. falciformis have declined by more than 70 percent in almost every area in which they are found. These declines are primarily due to overexploitation by fisheries supplying fin products for international trade.

Based on Food and Agriculture Organization of the United Nations’ productivity category, silky shark populations are vulnerable to depletion and will be slow to recover from over-exploitation.

The thresher sharks are three species: common thresher shark (alopias vulpinus), big-eyed thresher shark (alopias superciliosus) and the smallest of the group, the pelagic thresher shark (alopias pelagicus).

Thresher sharks are highly migratory pelagic sharks, with an almost worldwide global distribution in tropical and temperate oceanic and coastal seas.

Thresher sharks can be most easily identified by the extremely long upper lobe of the caudal fin, which can be as long as the shark’s body. They have a short head and a cone-shaped nose. The first dorsal fin is tall and erect, and the pectoral fins are elongated.

The thresher shark uses its tail to stun its prey, and its large caudal fin may be caught on pelagic longlines as a result of the shark’s attempts to stun the bait.

They are highly migratory pelagic sharks, with an almost worldwide global distribution in tropical and temperate oceanic and coastal seas. Bigeye thresher sharks are a high-trophic-level predator in ocean ecosystems, feeding mainly on pelagic fishes, as well as squid.

There are marked declines in bigeye thresher shark populations, driven partly by the high value of its fins in international trade.

The very low intrinsic reproductive rate of the thresher sharks makes them among the most vulnerable of all shark species to fishing worldwide, whether as a target or bycatch species.

For the big eye thresher shark, the female matures at 13 years old, the gestation lasts 12 months and a litter averages only two pups.

Thankfully, the thresher shark fins appearing in the Hong Kong shark fin market has declined 77-99% in the past ten to 15 years.

Both types of sharks qualify for inclusion in Appendix II because international trade in this species’ fins is a major driver of the unsustainable and largely unmanaged fisheries that have caused marked declines in its populations worldwide.

An Appendix II listing for silky shark and thresher sharks species will ensure that international trade is supplied by sustainably managed and accurately recorded fisheries that are not detrimental to the status of the wild populations they exploit.

--EM

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