Sharks use their highly developed senses to locate their prey. That is particularly important in the open sea. Did you know that there is an oceanic shark locating its prey by the sound of other predators? Unlike the oceanic whitetip shark (who uses the smell above the water surface), the Silky shark is able to find feeding dolphins, tunas or seabirds in the wide open ocean by sound to join in the fun as soon as possible. Sadly, the above mentioned irregular pulsed sounds of feeding competitors resemble the rotor frequency of U.S. Coast Guard helicopters, as transmitted underwater. That means, that helicopter attract Silky sharks.
Von Alex Chernikh – Фото Алекса Черных, Гардинес де ла Рейна, Куба, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=2138939
The Silky shark (Carcharhinus falciformis) is a species of requiem sharks and named for the smooth texture of its skin which is densely covered by tiny, overlapping diamond-shaped denticles. It reaches up to 10 ft -3 m- length with an average of 8 ft – 2.5 m. The female is viviparous: each of the 2 to 14 embryos has got its own separate compartments in the two uteri of the mother, and once it exhausts its supply of yolk, the depleted yolk sac is converted into a placental connection through which the mother delivers nourishment. The newborn pups are relatively small (up to 30 in -75 cm- long), but grow rapidly (45 in -115 cm- at one year) in sheltered reef nurseries and stick together before moving into the open ocean.
Like every oceanic predator, the Silky shark feeds opportunistic. Its favorite prey are tuna, which makes them the most commonly caught species of shark as bycatch in tuna fisheries around drifting FADs (fish magnets). But it is targeted by both commercial and artisanal pelagic fisheries all over the world, too – being among the most abundantly represented species in Asian shark fin markets and by far the most common source of shark jaws trophies.
The Silky shark is abundant all over the world in tropical and warm temperate, coastal and open waters, at least it was. Mounting evidence indicates the silky shark has declined substantially worldwide (despite under-reporting, lack of species-level separation and problematic identification in fishery data). In 1989 alone, some 900,000 individuals were taken as bycatch in the southern and central Pacific tuna longline fishery. Together with its generation period of 11 years, it resulted in a classification of near threatened worldwide and vulnerable in the eastern central and southeastern Pacific and the northwestern and western central Atlantic since 2007. Since it is a highly migratory species, states are urged to cooperate over the management of these species by the UN Convention on the Law of the Sea. I hope this happens soon.