Galapagos shark

Galapagos shark (Carcharhinus galapagensis) is also known as the “grey reef whaler” or “mackerel shark.” In the Galapagos Islands you may hear locals call it cação (Portuguese), tiburón de Galapagos (Spanish), tollo (Spanish), or tollo-cazón (Spanish). Their name makes it sound like they stay just in the archipelago islands off of Ecuador, but they are actually pretty circumtropical in distribution. They prefer inshore waters (with strong currents and over a rocky bottom or coral reef), but have been reported offshore and crossing between islands. Juveniles tend to stick to their shallow waters, safe from predators- including their own parents! Both as juveniles and adults, these sharks are commonly seen in loose groups, patrolling the bottom.

A defined range has not been described for these animals due to them being confused with other sharks. This is a large shark (can reach up to 3.7 m/12 ft), with a brown-grey dorsal side and a white underbelly. There may or may not be dark markings on their fins (it really depends on the individual). A white band on their flanks can also sometimes be seen. They have a slender body, and a tall first dorsal fin with a pointed tip. They also have a broad, rounded nose.

The Galapagos shark and the grey reef shark (C. amblyrhyncos) look a lot alike, with the Galapagos shark having a more slender body and a rounder tip on its first dorsal fin. The dusky shark (C. obscurus) and Galapagos shark are also strikingly similar; the Galapagos shark has a more erect first dorsal fin and larger teeth. The foolproof way to tell these latter two species apart? Number of precaudal vertebrae. This means scientists have to look at the back of their spine from the back of its skull to the base of its tail. This is a fatal practice. There are about 103-109 precaudal vertebrae (before the caudal tail) in the Galapagos shark, and 86-97 in the dusky shark.

These sharks are one of the known sharks to display threatening gestures to warn competitors or those trespassing in their home territory. Threatening displays include the arching of the back, raising the head, and lowering the caudal and pectoral fins while swimming in a twisted, rolling motion. Galapagos sharks feed on fish (including eels) and slippery squid and octopus. As they grow, they do sometimes exhibit cannibalism.​

They get sexually mature at around 10 years, with a maximum lifespan of about 24 years. Galapagos sharks are viviparous, giving live birth to litter sizes that vary from 4-16 pups. The IUCN has assessed them as Near Threatened (NT).

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glossary

• Circumtropial: Surrounding or distributed throughout the tropics.
• Flank: Sides of the animal.
• IUCN: International Union for Conservation of Nature.
• Pectoral fins: Fins located behind the gills on either side.
• Precaudal: Anterior to the tail.
• ​Pup: Give birth to baby sharks (pups).
• Pups: Baby sharks.
• Viviparous: Eggs hatch inside the female's body and the babies are fed by a placenta which transfers nourishment from the mother to the babies (via an umbilical cord which is connected to the baby shark between the pectoral fins).​

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