Silky Shark

The silky shark (Carcharhinus falciformis), a member of the family Carcharhinidae, is distinguished by the smooth texture of its skin. It is also known by several other names, including blackspot shark, gray whaler shark, olive shark, ridgeback shark, sickle shark, sickle-shaped shark, and sickle silk shark. This species ranks among the most abundant sharks in the pelagic zone, thriving in tropical waters across the globe. Notably migratory and mobile, the silky shark is typically observed over the continental shelf at depths reaching 50 meters (164 feet). With its slender, streamlined body, the silky shark can grow to a length of approximately 2.5 meters (8 feet 2 inches). It is easily identifiable by its comparatively small first dorsal fin, with a curving rear margin, a tiny second dorsal fin with an elongated free rear tip, and long, sickle-shaped pectoral fins. The species exhibits a deep, metallic bronze-gray coloration on its dorsal side and a white underside.

Silky sharks, renowned for their impressive hunting prowess in their oceanic habitat where prey can be scarce, primarily target bony fishes and cephalopods. They employ sophisticated hunting techniques, such as corralling prey into compacted schools before initiating open-mouthed, slashing attacks. These sharks often trail schools of tuna, which are a preferred prey. Their acute sense of hearing enables them to detect low-frequency noises emanating from other feeding animals, which can lead them to potential food sources. Remarkably, silky sharks are viviparous, with developing embryos sustained through a placental connection to the mother. Geographical variations exist in the life history of this species, with reproduction occurring year-round except in regions like the 🌊 Gulf of Mexico, where it is seasonal. Females may give birth to litters of up to 16 pups, either annually or biennially. The newborns initially inhabit sheltered reef nurseries on the continental shelf's outer areas, where they grow before venturing into open waters.

Despite their large size and sharp teeth rendering them potentially dangerous, interactions with humans are infrequent due to their oceanic habitat. Nonetheless, they can exhibit aggressive behavior towards divers. The silky shark is targeted for its fins and, to a lesser extent, for its meat, hide, liver oil, and jaws. Their abundance places them as a significant component of commercial and artisanal shark fisheries globally. They are often bycatch in tuna fisheries, owing to their close association with tuna. Although previously believed to be resilient to fishing pressures due to their wide distribution and considerable population, evidence indicates declining numbers worldwide. Consequently, the International Union for Conservation of Nature (IUCN) reclassified the silky shark as Vulnerable in 2017.

The silky shark is among the three most prevalent pelagic sharks, alongside the blue and oceanic whitetip sharks, and stands as one of the most numerous large oceanic animals, with an estimated population in the tens of millions. Unlike the other two species, the silky shark is less strictly pelagic, commonly found in offshore waters near land where food is more accessible. As an active, inquisitive, and aggressive predator, the silky shark often defers to the slower but stronger oceanic whitetip shark in competitive scenarios. When investigating potential interest points, it may appear inattentive, gently circling, and occasionally swinging its head. However, it can respond swiftly to environmental changes. Silky sharks are often found near floating objects such as logs or tethered naval buoys.

Juvenile silky sharks are known to form large, loosely organized groups, likely for mutual protection. During migrations, aggregations can encompass over a thousand individuals, often segregated by size and sometimes, in the Pacific, by sex. Within these groups, individuals exhibit behaviors such as tilting, jaw gaping, and gill puffing. Occasionally, they may charge towards the surface before veering away. The significance of these behaviors remains uncertain. When confronted, silky sharks may display threats by arching their backs, lowering their tails and pectoral fins, raising their heads, and swimming in tight loops with a stiff demeanor, often turning broadside to perceived threats. Potential predators include larger sharks and killer whales (Orcinus orca). Known parasites include the isopod Gnathia trimaculata, copepod Kroeyerina cortezensis, and tapeworms Dasyrhynchus variouncinatus and Phyllobothrium species. Silky sharks frequently intermingle with scalloped hammerheads (Sphyrna lewini) and have been observed following marine mammals.

Silky sharks are opportunistic feeders, primarily preying on bony fishes throughout the water column, such as tuna, mackerel, sardines, mullets, and others. They also consume squid, paper nautilus, and swimming crabs, and fossil evidence suggests scavenging on whale carcasses. Large groups can form around good feeding opportunities, herding fish into a bait ball and consuming them. During feeding, silky sharks charge through compacted fish schools, capturing prey at the corners of their jaws. Studies in regions like Florida and the 🇧🇸 Bahamas demonstrate their sensitivity to low-frequency sound, particularly attracting them to feeding activity noises. They are known for quickly withdrawing when the sound character changes but eventually habituate to such changes.

The silky shark's formidable size and dentition categorize it as potentially dangerous to humans, although contact is minimal due to their pelagic nature. Curiosity may draw them to approach divers closely and persistently, and they can become excited in the presence of food. The silky shark exhibits more aggressive tendencies when encountered on reefs compared to open water. Reports exist of sharks harassing divers, prompting their exit from the water. As of May 2009, the International Shark Attack File has recorded six attacks attributable to silky sharks, none of which were fatal.