Silky shark  (Carcharhinus falciformis)

The silky shark is classified as Near Threatened (NT) on the IUCN Red List (1).

A streamlined predator, the silky shark (Carcharhinus falciformis) gets its common name from its exceptionally smooth skin, which has an almost metallic tone. The upperparts of the silky shark range between brown, bronze and grey, while its underparts are white (3).

The tail of the silky shark has a slightly larger upper than lower lobe, which provides good thrust for catching fast-moving prey, as well as lift to keep the shark from sinking. The pectoral fins are long and slender, and there are two dorsal fins, the second of which is considerably smaller than the first. The dorsal fins are often darker than the rest of the body (3). The silky shark has relatively large eyes, and small teeth that are heavily serrated on both sides to help grip slippery prey (4).

The female silky shark is generally slightly larger than the male (4).

The silky shark is widespread across the Atlantic, Pacific and Indian Oceans. It is most commonly seen in the Red Sea, the waters surrounding the Bahamas, and at Cocos Island off Costa Rica (3) (4).

The silky shark is a pelagic species, mainly occupying open tropical seas. It has been recorded in waters from 18 to 500 metres deep (3). Adult silky sharks are typically found in deep waters, while smaller individuals are often found in shallower coastal waters (4).

The silky shark favours warm water, around 23 degrees Celsius, and tends to remain near the surface (4).

The silky shark is an active predator that feeds primarily on pelagic bony fish such as mackerel, tuna and mullet. It also feeds on cephalopods, such as squid, which are found at greater depths, and has also been known to occasionally eat crustaceans such as crabs. In the Pacific Ocean, large numbers of silky sharks have been observed gathering around tightly packed shoals of small fish, known as ‘bait balls’ (3) (4).

The silky shark can be both a solitary and social species (2). Interestingly, it often shoals with individuals of its own size, although segregation by sex is not strongly shown (4).

Female silky sharks are viviparous, meaning the embryos develop inside the female without an egg case and are born live (5). The silky shark has a long gestation period of 12 months, and the typical litter size is between 2 and 14 young. The young silky sharks are typically born in late spring, around May or June, and each measures 70 to 85 centimetres at birth. Male silky sharks mature at 9 to 10 years old, while females mature at 12 years. The typical lifespan of the silky shark is believed to be about 23 years (4).

Due to its beautifully marked skin, the silky shark is a popular target for the shark leather trade. Like many other sharks, it is also fished for its fins, meat and liver oil (5). The silky shark is ranked in the top three most important sharks in the global fin trade, with up to 1.5 million fins being traded annually from this species (1).

As well as being deliberately targeted by fisheries, the silky shark also suffers from being caught as bycatch, in particular by fishing methods such as purse seines and long lines. It is the most frequent species of shark caught by purse seines used to fish tuna in the eastern Pacific Ocean (1).

Despite these threats, a lack of information about the silky shark’s population numbers means it is not clear exactly how threatened this species is (4).

There are currently no international limits placed on catches of the silky shark, nor is it the focus of any other specific conservation measures (1).

However, some areas inhabited by the silky shark are protected, such as Cocos Island and its surrounding ecosystems, which are protected against fishing by the Costa Rican government (6).

Find out more about shark conservation:

• Bite-Back: Shark and Marine Conservation:
  http://www.bite-back.com/
• Shark Trust:
  http://www.sharktrust.org/
• Save Our Seas Foundation:
  http://www.saveourseas.com/
• Project AWARE:
  http://www.projectaware.org/