The blacktip reef shark ( Carcharhinus melanopterus) is a fascinating and commonly encountered shark species in the Indo-Pacific region. Recognizable by the distinctive black tips on its fins, this shark plays a vital role in the health and balance of coral reef ecosystems. This article explores various aspects of the blacktip reef shark, with a focus on its dietary habits and ecological role.
Identification and Physical Characteristics
Blacktip reef sharks are named for the characteristic black tips or margins on their fins, often accented with white highlights. They are a small to medium-sized shark with a short, round snout and angled, saw-like teeth. The body is fusiform (spindle-shaped), well-suited for efficient swimming. Coloration provides camouflage; a dark back helps them blend in with the dim seafloor when viewed from above, while a white belly blends in with the brighter ocean surface when viewed from below. This countershading helps them to ambush prey and avoid predators.
Key features include:
- Fin Markings: Prominent black tips on the first dorsal fin and lower caudal lobe, with less prominent black tips on other fins.
- Body Shape: Moderately sized body with a short, bluntly rounded snout.
- Teeth: Narrow, serrated upper teeth with an erect to oblique cusp and cusplets; lower teeth are also narrow with finely serrated edges.
- Coloration: Brown-tan on the dorsal surface with white countershading on the underside. A light band extends along the flank from the anal fin to just above the pectoral fins.
- Size: Maximum size is generally less than 160 cm (5.2 ft), though individuals have been recorded up to 180 cm (5.9 ft). They are born at 33-59 cm (1-2 ft). Males mature between 91-100 cm (3-3.3 ft) and females between 96-112 cm (3.1-3.7 ft).
The grey reef shark (Carcharhinus amblyrhynchos) may be confused with the blacktip reef shark. However, the grey reef shark can be distinguished by its stockier body and lack of black tip on the dorsal fin.
Habitat and Distribution
The blacktip reef shark is commonly found throughout the tropical Indo-Pacific. Their range includes waters surrounding Thailand, China, Japan, the Philippines, Indonesia, Malaysia, Papua New Guinea, New Caledonia and northern Australia. They are one of the most common reef sharks at islands in the Pacific Ocean, as far east as the Hawaiian Islands. The species is also present in South Africa, Mauritius, Seychelles, Madagascar, the Red Sea, Pakistan, India, Sri Lanka and the Maldives.
Read also: What do reef sharks eat?
Blacktip reef sharks prefer shallow, clear water and are commonly found on coral reefs, reef and sand flats, over reef drop offs, in atolls or along continental and insular shelves, including tidal movements into mangrove environments. They occur in the Indo-Pacific from the Red Sea and East Africa to the Hawaiian Islands and French Polynesia. Found in shallow inshore waters on coral reefs, in the intertidal zone (reef flats) and near reef drop-offs. Also found in mangrove areas, moving in and out with the tide. This shark cruises in very shallow water with its dorsal (top) fin often extending above the surface.
They inhabit:
- Shallow inshore waters
- Coral reefs
- Reef flats (intertidal zone)
- Near reef drop-offs
- Mangrove areas (moving in and out with the tide)
They have small home ranges, exhibiting strong site fidelity and restricted movements that appear to be closely tied to the distribution of coral reef habitat. Long distance movements over oceanic expanses appear uncommon. The average daily activity space of this species was estimated to be ~10 km2.
Diet and Feeding Behavior
Blacktip reef sharks are daytime hunters that feed in small groups, preying mostly on tropical reef fishes and cephalopods. Their diet consists primarily of teleost fishes, crustaceans, cephalopods, and other molluscs. Common prey includes surgeonfish and mullet.
Specific prey items include:
Read also: What Do Reef Triggerfish Eat?
- Small fish (i.e. mullet, groupers, theraponids, jacks, mojarras, slipjaws, wrasses, surgeonfish, sillinginids)
- Mollusks (i.e. cuttlefish, squid, octopi)
- Crustaceans (i.e. crabs, shrimp)
Blacktips have been observed working in coordination to drive schools of mullets close to the shoreline, making feeding easier. This cooperative hunting strategy demonstrates their intelligence and adaptability. They have long, thin, serrated teeth suited for their diet of reef fish. The teeth are located in rows, which rotate after teeth become worn down or broken off.
Reproduction and Life Cycle
Blacktip reef sharks are live-bearing, nourishing pups in utero via a yolk-sac placenta. Both annual and biennial reproductive cycles have been reported across various parts of the range. Parturition and mating generally occur during the summer and early autumn though gestation also varies with location from 8-9 months, 10-11 months, and 16 months. Most litters contain 2-4 pups. There is regional variation in size at birth, size at maturity and maximum size.
Key reproductive traits:
- Viviparous: Live-bearing with yolk-sac placenta.
- Reproductive Cycle: Both annual and biennial cycles observed.
- Gestation: Varies with location (8-9 months, 10-11 months, or 16 months).
- Litter Size: Typically 2-4 pups.
Interactions with Humans
Blacktip reef sharks have occasionally been known to bite people that are swimming or wading but do not pose a serious threat to humans. Due to its smaller size, this species is not typically regarded as a danger to humans. Blacktips have, however, been known to be aggressive toward humans engaged in spear-fishing. Additionally, people wading in shallow water have suffered bites upon their feet and legs from this species.
They are abundant on coral reefs, making them a popular species in reef and dive tourism. This can provide economic benefits to local communities, but also requires responsible management to minimize disturbance to the sharks and their habitat.
Read also: Diet and Habitat of Grey Reef Sharks
Conservation Status and Threats
Blacktip reef sharks are considered “Near Threatened” according to the International Union for the Conservation of Nature (IUCN) threatened species criteria. Population bottlenecks have been reported in some regions but may not be an accurate reflection of overall population trends. They are known to be locally abundant in other parts of their range.
Blacktip reef shark are caught by inshore fisheries throughout some parts of their distribution. They are utilized for fins, meat and liver oil but have limited commercial value due to their small size. Blacktips are occasionally targeted for human consumption. During the wet season, Australian Aborigines will harvest blacktips and prepare them as buunhdhaarr - a dish in which the liver and flesh of the shark are boiled separately and then minced and mixed together for final consumption. Elsewhere, the flesh of blacktips are prepared fresh or dry-salted.
Threats to the blacktip reef shark include:
- Overfishing: They are caught for their fins, meat, and liver oil. Due to their slow reproductive rate, the population is declining worldwide.
- Habitat Loss: The shark's preference for in-shore waters makes it particularly vulnerable to coastal development, which eliminates critical habitat such as nursery sites.