Silky Shark

They prefer to feed on bony fishes and cephalopods and have been known to drive them into compacted schools before launching forward and attacking, open-mouthed. They love trailing schools of tuna, which are some of their preferred prey.

Silky Shark Facts

• Silky Sharks are highly mobile and migratory.
• They are swift, inquisitive, and persistent hunters.
• Tuna is a favored prey of the Silky Shark.

Classification and Scientific Name

Silky Sharks (Carcharhinus falciformis) are also known by numerous other names, such as grey whalers, blackspot sharks, olive sharks, ridgeback sharks, and sickle sharks. They are a species of requiem shark in the family Carcharhinidae and are named for the smooth texture of their skin.

Identification and Appearance

The Silky Shark has a slender, streamlined body and will typically grow to a length of 2.5 m (8 ft. 2 in.). It can be distinguished from other large requiem sharks by its relatively small dorsal fin that has a curving rear margin. Its second dorsal fin is very tiny with a long free rear tip. It also has long, sickle-shaped pectoral fins. The Silky Shark is a deep, metallic bronze-gray above and white below.

Habitat

Although this shark is essentially pelagic, it is not restricted to only the open ocean. They have been recorded from depths as shallow as 18 meters (56 ft). It is a very swift, active shark that prefers to be in warm waters of about 23 degrees C. It is most commonly found near the edges of continental shelves and over deep water reefs, where they are able to find an abundance of food. Silky Sharks typically reside in water anywhere from the surface, down to at least 500 meters (1,550 ft), but they’ve been caught in water as deep as 4,000 meters (12,400 ft)!

Typically, smaller Silky Sharks can be found in coastal nurseries, and the adults further offshore in the deeper waters. Small Silky Sharks are commonly associated with schools of tuna since that is one of their preferred prey. Silky Sharks grow fast when they’re young since they are considered prey for many other larger sharks and killer whales. They are usually safe from these types of predators while they are in the nurseries. When they reach adulthood, they swim out into the open ocean.

Conservation

Being one of the most abundant and widely distributed sharks on the planet, the Silky Shark was at one time thought to be immune to depletion, despite heavy fishing mortality. In 1989, there were 900,000 Silky Sharks taken as bycatch in the southern and central Pacific tuna longline fishery, seemingly without any effect on the total population. The fishery data on the Silky Shark is often confounded by under-reporting, misidentification, and lack of species-level separation. Nevertheless, there is still mounting evidence that the Silky Shark has indeed declined substantially worldwide. This has been a consequence of its modest reproduction rate, which is unable to sustain the high levels of exploitation it’s faced.

The Silky Shark is classified by the International Union for Conservation of Nature as a vulnerable species. These sharks would also greatly benefit from a ban on shark finning, which is being increasingly implemented by various nations and supranational entities. Recent steps to improve fishery monitoring include the expansion of electronic monitoring on longliners and the use of bycatch release devices to reduce instances of shark bycatch. However, given the highly migratory nature of these sharks and their association with schools of tuna, there is no simple way that is known to be able to reduce bycatch without also affecting the economics of the fishery.

Predators of Silky Sharks

The predators of Silky Sharks include killer whales (Orcas), large sharks, and humans. Humans reduce the population of the Silky Shark through inadvertent fishery methods, as well as the intentional use of their flesh and fins for food in some cases. They are also known to be used for their hide for leather, and their liver for oil. It is estimated that the Silky Shark population has decreased by 85% over the course of a 19 year period from 1984 to 2005. Unfortunately, the population continues to decrease.

Silky Sharks are also one of the three most traded shark species in the global shark fin trade. They are among some of the most common bycatch species in the tuna process and are one of the most common sources of cleaned and dried shark jaws that are sold to tourists in tropical countries. Due to these types of practices, the population of the Silky Shark has continued to drop dramatically over the years, prompting the assigned status of Vulnerable from the IUCN. Not only are Silky Sharks at risk of exploitation due to fishery practices and accidental catches with tuna, but they are also specifically targeted because of their fins. There is a high demand for shark fins in Asia, which means that even though they are considered to be accidental bycatch, they are still worth keeping because of the value of their fins. There have been many efforts put forward recently to help conserve and protect Silky Sharks from exploitation that have been shown to have made a positive impact on the population.

Reproduction and Lifespan

On average, Silky Sharks live to be about 23 years of age, and it is estimated that they can live up to 25 years in the wild. Their reproductive maturity is reached at 7 to 9 years of age and 6.89 to 7.55 feet (2.1 to 2.3 meters) in females. For males, it is 6 to 7 years and 5.9 to 6.89 feet (1.8 to 2.1 meters). When they’re in tropical waters, Silky Sharks can be bred year-round, and in waters like the Gulf of Mexico, they can only breed during the summer months (June, July, and August). They are known to breed once every two years and are typically able to produce between two and 14 live offspring per litter.

Like other members of its family, the Silky Shark is known as viviparous: once the developing embryo exhausts its supply of yolk, the depleted yolk sac is then converted over into a placental connection, through which the mother will then deliver further nourishment. Relative to other types of viviparous sharks, the placenta of Silky Sharks is less similar to the analogous mammalian structure in that no interdigitation exists between the tissues of the fetus and those of the mother.

Also, the red blood cells of the fetus are much smaller than the maternal blood cells, which is the opposite of the pattern that would normally be seen in mammals. Adult female Silky Sharks have a single functional ovary (on the right side) and two functional uteri, which are divided lengthwise into two separate compartments for each embryo.

Females give birth after a gestation period of 12 months, either every year or every other year. The pups are born in reef nursery areas that are located on the outer continental shelf, where there are ample food supplies and protection from large pelagic sharks that would prey on them. Being under the risk of predation has been selected for fast growth in young sharks, which adds anywhere from 25 to 30 cm (9.8- to 11.8 in) to their length within their very first year of life. After a few months, or by the first winter in the Gulf of Mexico, the sharks (now adults) migrate out of the nursery and into the open ocean.