Carcharhinidae: requiem sharks

The requiem sharks belong to the family Carcharhinidae within the order Carcharhiniformes. They are migratory sharks that inhabit warm seas, although some can be found in freshwater or brackish water. Species in this family include the bull shark, lemon shark, spinner shark, blacknose shark, blacktip shark, grey reef shark, blacktip reef shark, silky shark, sandbar shark, blue shark, copper shark, oceanic whitetip shark, and whitetip reef shark.

Members of this family exhibit the typical characteristics of carcharhiniforms. Their eyes are round and one or two gill slits are situated over the base of the pectoral fin. Most species are viviparous, giving birth to fully developed young. They vary significantly in size, from just 69 cm adult length in the Australian sharpnose shark to 4 m in the oceanic whitetip shark. Scientists believe the size and shape of their pectoral fins are designed to minimize transport costs. Requiem sharks usually live in tropical areas but migrate regularly. Females release a chemical in the water to indicate to males that they are ready to mate, with the mating season generally between spring and autumn.

These sharks are among the top five species involved in attacks on humans; however, due to the difficulty in identifying individual species, attack records may be inaccurate.

Origin of the name: etymology

The common name "requiem shark" may be related to the French word for shark, "requin," whose origin is controversial. One theory suggests it derives from the Latin "requiem" (rest), creating a cyclical etymology (requiem-requin-requiem). Another theory derives it from the old French verb "reschignier" (to make a grimace showing teeth).

The scientific name "Carcharhinidae" was first proposed in 1896 by DS Jordan and BW Evermann as a subfamily of Galeidae (now replaced by Carcharhinidae). The term comes from the Greek "κάρχαρος" (karcharos, sharp or jagged) and "ῥί̄νη" (rhinē, rasp), describing the rough and jagged skin. This type of skin is common in sharks in general, not just in Carcharhinidae.

Evolution and History

The oldest member of the family is Archaeogaleus lengadocensis from the Lower Cretaceous (Valanginian) of France. Only a few records of the group are known before the Cenozoic. Modern carcharhinid sharks have diversified widely in coral reef habitats.

Hunting Techniques

Requiem sharks are fast and efficient hunters. Their elongated torpedo-shaped bodies make them agile swimmers, allowing them to attack their prey with ease. Some species are continuously active, while others can rest motionless on the bottom. They feed on a variety of sources, including bony fish, squid, octopus, lobsters, turtles, marine mammals, seabirds, other sharks, and rays. Smaller species tend to have a more specific diet, while some large species, like the tiger shark (Galeocerdo cuvier), are practically omnivorous, even consuming trash. These sharks are migratory and follow their prey across oceans. They are more active at night, taking advantage of their good vision to hunt. Most requiem sharks hunt alone, but some species, like whitetip reef sharks and lemon sharks, may hunt in groups, performing coordinated attacks against their prey. Some species display specific behaviors when encountering divers or other sharks, which may indicate an aggressive or defensive threat.