A fast and energetic requiem shark
The Blacktip shark (Carcharhinus limbatus) is a species of requiem shark, and part of the family Carcharhinidae. It is common to coastal tropical and subtropical waters around the world, including brackish habitats. Blacktip sharks migrate and sometimes in very large aggregations right here off our South Florida coast; its quite a sight to see. Blacktip sharks also perform a spinning leap out of the water when attacking fish.
Photo: © 2018, Harry Stone, Planet Shark Divers, all rights reserved.
Family: Carcharhinidae – Requiem sharks
Common Name– Ground Sharks
Common Name– Requiem Sharks
Status: IUCN Red List NEAR THREATENED
Average Size and Length: The maximum length known of the Blacktip shark is 9.2 feet, though 4.9 feet is more typical.
Average Weight: The maximum recorded weight known is 271 pounds.
Teeth and Jaw: The jaws of the Blacktip shark contain 15 tooth rows on either side, with two symphysial teeth in the upper jaw and one symphysial tooth in the lower jaw. The teeth are broad-based with a high, narrow cusp and serrated edges.
Head: It has a long, pointed snout with small eyes.
Demographic, Distribution, Habitat, Environment and Range: Around February, us local to Stuart, Jupiter Island, Jupiter and Palm Beach and the rest of South Florida are in for a treat, we are able to watch the biggest long-distance seasonal congregation and migration of Blacktip sharks off the coast of Palm Beach, Florida. Thousands of Blacktip sharks, over 10,000 to be exact cruise the shore for warmer waters during winter. This is a little further north lately; typically, Broward and Miami/Dade are perfect water for them. Jupiter is a little chilly.
Typically, the Blacktip shark has a worldwide distribution in tropical and subtropical waters. In the Atlantic, it is found from Massachusetts to Brazil, including the Gulf of Mexico and the Caribbean Sea, and from the Mediterranean Sea, Madeira, and the Canary Islands to the Democratic Republic of the Congo. It can be found all around the periphery of the Indian Ocean, from South Africa and Madagascar to the Arabian Peninsula and the Indian subcontinent, to Southeast Asia. In the western Pacific, it is found from the Ryukyu Islands of Japan to northern Australia, including southern China, the Philippines and Indonesia. In the eastern Pacific, it can be found from Baja California to Peru. It has also been reported at a number of Pacific islands, including New Caledonia, Tahiti, the Marquesas, Hawaii, Revillagigedo, and the Galápagos.
Blacktip sharks are found in water typically less than 98 feet deep over continental and insular shelves, though they may dive to 210 feet. They prefer muddy bays, island lagoons, and the drop-offs near coral reefs; and are even tolerant of low salinity and enter estuaries and mangrove swamps. Sometimes Blacktip sharks can be found offshore, but this is not typical because they do not inhabit oceanic waters. Although an individual may be found some distance offshore, blacktip sharks do not inhabit oceanic waters.
Diet: Blacktip sharks feed dawn and dusk. They are extremely social and have high energy. This can contribute to feeding frenzies when there are large quantities of food. One example is if a commercial boat dumps overboard.
The primary food source for Blacktip sharks is fish. Fish make up 90% of the Blacktip shark’s diet. Some of these fish include herring, sardines, anchovies, ladyfish, sea catfish, cornetfish, flatfish, threadfins, mullet, mackerel, groupers, snook, porgies, mojarras, emperors, grunts, butterfish, tilapia, triggerfish, boxfish, porcupinefish, and jacks. They may also eat skates, rays and even smaller sharks like Smoothhounds and Sharpnose sharks. On occasion they will eat crustaceans and cephalopods. In South Africa, Blacktip sharks mostly eat herring and jacks. In the Gulf of Mexico, they primarily eat menhaden.
Aesthetic Identification: The Blacktip shark is fusiform, streamlined and robust with 5 pairs of long gill slits. They are grey to brown on top, and counter-shaded white on the bottom. They have a white stripe running along the sides. Blacktip sharks can temporarily lose almost all their colors during blooms, or “whitings”, of coccolithophores. The pectoral fins, second dorsal fin, and the lower lobe of the caudal fin usually have black tips. The pelvic fins and rarely the anal fin may also be black-tipped. The first dorsal fin and the upper lobe of the caudal fin typically has black edges. Some larger individuals have unmarked or nearly unmarked fins. The first dorsal fin is tall and falcate with a short free rear tip; no ridge runs between the first and second dorsal fins. The large pectoral fins are falcate and pointed.
Biology and Reproduction: Some parasites of the Blacktip shark include the copepods Pandarus sinuatus, smithii, and the monogeneans Dermophthirius penneri and Dionchus. These attach to the shark’s skin. Nematodes Philometra Philometridae infest the ovaries.
The Blacktip shark can be found in groups. Segregation by sex and age does not occur; adult males and nonpregnant females are found apart from pregnant females, and both are separated from juveniles. There are some areas in Florida of designated aggregation nursery areas that are apparent during the day, and disperse at nightfall. They aggregate most strongly in the early summer when the sharks are youngest, suggesting that they are seeking refuge from predators (mostly larger sharks) in numbers. Predator avoidance may also be the reason why juvenile Blacktips do not congregate in the areas of highest prey density in the bay.
The Blacktip shark is viviparous. Litters are usually sized between 4 and 7 every other year. Mating occurs from spring to early summer, and the young are born around the same time the following year after a gestation period of 10–12 months.
The growth rate of the Blacktip shark slows with age, and the size at maturity varies upon location. The age at maturation is 4–5 years for males and 7–8 years for females. The lifespan is at least 12 years.
In 2007, a 9-year-old female Blacktip shark at the Virginia Aquarium and Marine Science Center was found to be pregnant with a single near-term female pup, despite having never mated with a male. Genetic analysis confirmed that her offspring was the product of automictic parthenogenesis, a form of asexual reproduction in which an ovum merges with a polar body to form a zygote without fertilization. Along with an earlier case of parthenogenesis in the Bonnethead, this event suggests that asexual reproduction may be more widespread in sharks than previously thought (Virginia Aquarium, 2007).
Some known nursery areas are Pine Island Sound, Terra Ceia Bay, and Yankeetown along the Gulf Coast of Florida, Bulls Bay on the coast of South Carolina, and Pontal do Paraná on the coast of Brazil. Although adult blacktip sharks are highly mobile and disperse over long distances, they are philopatric.
Behavioral Traits, Sensing and Intelligence: The Blacktip shark is known to leap out of the water and spin three or four times about its axis before landing. Some documentations suggest that sometimes these jumps happen after a feeding. They corkscrew vertically through schools of small fish and its momentum launches it into the air. Research in the Bahamas suggest that Blacktip sharks may also jump out of the water to dislodge attached sharksuckers which irritate the shark’s skin and compromise its hydrodynamic shape.
Blacktip sharks are shy and timid, and usually lose to other sharks when it comes to catching prey.
If threatened or challenged, they may perform 25 seconds of an agonistic display: the shark swims towards the threat and then turns away, while rolling from side to side, lowering its pectoral fins, tilting its head and tail upwards, and making sideways biting motions.
Speed: The Blacktip shark is extremely fast and energetic. They do engage in air spins. The speed attained by the shark during these jumps has been estimated to average 21 ft/s.
Blacktip Shark Future and Conservation: Here in Florida (As well as other parts of the Caribbean and South Africa), the Blacktip shark is target by fisherman to catch for sport because it is a strong and steady fighter, and the out of water leaps make it more of a challenge. It is listed as a game fish by the International Game Fish Association, however, here in Florida we are fighting to put an end to land-based shark fishing.
The United States and Australia are the only two countries that manage fisheries catching Blacktip sharks. No conservation plans specifically for this species have been implemented.
As one of the more common large sharks in coastal waters, the Blacktip shark is caught in large numbers by commercial fisheries throughout the world, using longlines, fixed-bottom nets, bottom trawls, and hook-and-line. The meat is of high quality and marketed fresh, frozen, or dried and salted. In addition, the fins are used for shark fin soup, the skin for leather, the liver oil for vitamins, and the carcasses for fishmeal. Blacktip sharks are one of the most important species to the northwestern Atlantic shark fishery. The flesh is considered superior to that of the sandbar shark, resulting in the sandbar and other requiem shark species being sold under the name “Blacktip shark” in the United States. The Blacktip shark is also very significant to Indian and Mexican fisheries, and is caught in varying numbers by fisheries in the Mediterranean and South China Seas, and off northern Australia.
Blacktip Shark Recorded Attacks on Humans: Blacktip sharks are curious about divers, but do stay a good distance away. They aren’t regarded as a high threat to humans since they are on the shy side, however food can increase their aggression and energy. As of 2008, the ISAF lists 28 unprovoked attacks (one fatal) and 13 provoked attacks. Blacktip sharks are responsible annually for 16% of the shark attacks around Florida, resulting in minor wounds.