Blacktip Reef shark
Blacktip Reef sharks (Carcharhinus melanopterus), are as the name suggests, associated with coral reefs. Other Reef sharks include Grey Reef sharks (Carcharhinus amblyrhynchos), Caribbean Reef sharks (Carcharhinus perezi) and Whitetip Reef sharks (Triaenodon obesus).
Blacktip Reef shark anatomy and appearance
The Blacktip Reef shark is a relatively small, streamlined shark with a blunt, wide, rounded snout and the mouth tucked underneath. They sport large pectoral fins that are shaped like a sickle. The sharks main color is grey to brown on top and white underneath, but they have distinctive black tips on the pectoral and dorsal fins. A strip of white is found underneath the black, which makes them stand out even more. There are small, flat, v-shaped scales covering their skin, called dermal denticles, which are more like small teeth than scales. These help with streamlining and therefore aid fast swimming, while also protecting sharks from parasites. This species has narrow teeth in their upper jaw and serrated teeth in the lower jaw. These allow the shark to grip and slice into their prey. They also have ampullae of Lorenzi that enables them to detect the location of prey from electrical currents prey emits. Blacktips have a nictating membrane, a translucent third eyelid that they can draw across for moisturisation and protection.
Growing up to an average of 1.9m and weighing 130kg, they are not the biggest shark, but they are fast. The fastest speed is currently unknown. As they prefer shallow water, they often swim with their dorsal fin exposed. Interestingly Blacktip Reef Sharks tend to be more active during the day, possibly because cooler night temperatures reduce their metabolism.
They are sometimes confused with the Blacktip shark (Carcharhinus melanopterus), and the two species do have a lot in common, but they rarely cross paths, as the Blacktip shark spends its time in cooler open waters.
Blacktip Reef shark habitat
Blacktip Reef sharks are found in shallow coastal waters throughout the Indo-Pacific, and strangely enough the Mediterranean Sea, which they accessed via the Suez Canal from the Red Sea. They have been recorded as far west as Tunisia. Preferring water temperatures of 15 to 24°C, they spend most of their time in shallow waters near the surface, with a maximum depth of 75m. Juveniles tend to prefer shallow sandy flats, whereas adults are normally found around reef ledges and drop-offs. Blacktips are social and tend to swim in groups. They are not migratory, and most Blacktips tend to spend 70% of their time in an area 0.3km2.
Natural predators to Blacktip Reef sharks include Tiger sharks (Galeocerdo cuvier) and Great White sharks (Carcharodon carcharias), so staying in shallow waters and in coral reefs affords them some protection from these.
Blacktip Reef shark diet
The diet of the Blacktip Reef shark mainly consists of small reef fish, but they are also known to feed on mullet and sturgeon. The sharks catch mullet by herding them onshore to strand them, a risky operation for a shark that needs to constantly keep moving to breathe. They also use pack hunting to their advantage to herd fish into a tight ball before going in for the kill. Less commonly Blacktips have been known to eat algae, coral, cuttlefish, octopus, squid, and shrimp. Around Palmyra Atoll (south of the Hawai’ian Islands), Blacktip Reef sharks even prey on seabird chicks that have fallen into the sea from their nests.
Blacktip Reef shark population
The average lifespan of the Blacktip Reef shark is estimated to be between 13 and 15 years. While males reach sexual maturity around the age of 4, females do not sexually mature until around 8 years, which means their reproductive span is very short. Coupled with long gestation periods (up to 11 months) and small litters (2-4 pups), the reproductive rate of Blacktip Reef sharks is low. Gestation periods for the sharks can vary wildly depending on habitat. Females in north Australia give birth after only 7 to 9 months. Scientists theorise this could be because of warmer waters off the coast of Australia.
Blacktip Reef sharks are viviparous, meaning they give birth to live young, rather than laying eggs. When they are born, pups range from 33 to 52cm long, and are free-swimming and independent as soon as they are born. They grow rapidly in the first few years of their lives. Females are able to reproduce asexually if there are no males present.
There are thought to be multiple subpopulations throughout its habitat range, with different genetic structures detected between island groups in the pacific. There has been limited sampling to date, so it is unknown how many subpopulations there are. It is estimated that the population of Blacktip Reef sharks has reduced globally by 30-44% over the last three generations spanning 44 years.
Blacktip Reef shark Conservation
Blacktip Reef Shark has most recently been assessed as vulnerable for The IUCN Red List of Threatened Species in 2020.
Threats to this species include commercial fishing for fins, liver oil, meat, and skins, although they have low commercial value to due to their small size. Most are taken as bycatch in general reef fisheries targeting teleost fish. Use of gill nets by fisheries also poses a threat to Blacktip Reef sharks, as they can get entangled in the nets, causing injuries and death, as they cannot swim to get oxygen. They are also targeted by sports fishers.
The biggest threat to Blacktip Reef sharks is loss of habitat; the coral reefs that they call home. Global climate change has caused large-scale coral bleaching events with increasing frequency. Almost all coral reefs worldwide have experienced local death of coral and local extinction of animals that inhabit them. Ocean acidification can also damage the physical structure of reefs. Destructive fishing practices in some areas, such as dynamite fishing, can cause declining water quality and declining coral reef habitat. This affects all creatures living amongst coral reefs, not just Blacktip Reef sharks.
This species is a common display species in public and private aquaria. It is exported live from countries such as Australia and Indonesia to aquaria worldwide.
There are no species-specific conservation management plans in place for Blacktip Reef sharks, however there are many general management measures such as Marine Protected Areas (MPAs) and shark sanctuaries , where targeted shark fishing is banned. On the Queensland east coast (including the Great Barrier Reef), shark catch for all species combined is managed through a limited entry license fishery with a maximum annual total allowable catch of 600 tonnes. Only in locations where fisheries are strictly regulated, where human population densities are low, or where dive-based tourism supports protection, are there low levels of threat that enable this species to thrive.
Blacktip Reef shark and humans
Blacktip Reef sharks can be curious about swimmers, but they are generally shy and easily frightened. They bend into an s-shape when they feel threatened. They are harmless unless provoked and most instances of biting involve hand feeding or spear fishing.
Their tendency to remain in specific territories makes them popular with divers and snorkelers, with the best places to see this species in the Maldives, Bora Bora, and Phi Phi Islands, Thailand. The video below is from a Shark Guardian led expedition to the islands of Phi Phi in Thailand to observe and collect data on the Black tip reef sharks.
Other interesting facts
Blacktip Reef sharks are one of the few shark species that can fully breach the water, usually during feeding frenzies. They have also been observed surfacing to look around in an action called ‘spy-hopping’.