This week’s featured species is known for their black tipped fins and large schooling migrations. The Blacktip Shark (Carcharhinus limbatus) is a moderately large, stout shark with a long, narrow, pointed snout and small circular eyes (Ebert, Fowler, & Dando, 2015). They have moderately large falcated fins with black tips on the pectoral, pelvic, both dorsal fins, and the upper lobe of the caudal lobe. Their gray-bronze bodies are flanked by a white stripe (Ebert, Fowler, & Dando, 2015).
Like many members of family Carcharhinidae, the blacktip shark spends most of its life in warm temperate and tropical waters over shallow reefs. They are known hunters of school bony fishes like sardines and anchovies, as well as soft bodies cephalopods and the occasional hard bodied crustaceans (Tricas et al., 1997). To accommodate a diet that mostly consists of soft, slippery bodied prey items, the blacktip shark has a set of jaws that are ideal for piercing and capturing these prey items. The teeth in the top and bottom jaw are very similar in shape. They are moderately long and erect. They are narrowly pointed with broader bases. The teeth in the upper jaw are coarsely serrated along the cusp, while the teeth in the lower jaw are finely serrated and curve slightly inwards (Huber, Weggelaar, & Motta, 2006).
If we knew nothing else about the blacktip shark, their eyes really would be a window into their soul as they give us a glimpse into their world. The structure of the blacktip shark’s eyes are common among neritic and pelagic species; these are species that spend their time in relatively shallow water and are often exposed to light during the day, as well as dark at night (Klimley, 2013). When exposed to light, their pupil contracts to a vertical slit with a small aperture at the bottom which is adapted to high irradiance intensities. At night, which the light or irradiance is a low intensity, the pupil dilates to a football shape (Klimley, 2013).
Every year, January to March, along Florida’s eastern coast something truly amazing happens. Thousands of blacktip sharks gather together to begin their seasonal migration along the coast, traveling as far north as Cape Cod (Bigelow & Schroeder, 1948). The cause of the great migration isn’t completely understood, however, researchers with Florida Atlantic University have been tagging some of these sharks to learn more about their movements and behaviors. In North America, female blacktip sharks give birth in the warmer months of May and June after mating in June and July the previous year (Burgess & Branstetter, 2009). It is possible this migration is related to pupping grounds and food availability for the neonates. Blacktip sharks in other regions of the world mate at different times, and thus pup at different times of the year. For example, blacktips in South Africa mate in November to December, and females pup the following October and November. Females require a year break between pregnancies, and so it takes 2 years for a female to complete a single reproductive cycle (Burgess & Branstetter, 2009).
HYDROPHILK (Videographer). (2017). Florida Shark Migration by Drone!!! | DJI Mavic Pro | Amazing 4K Footage [Video Clip]. Retrieved from https://www.youtube.com/
The blacktip shark is often misidentified with two other species of shark it shares its habitats with: the blacktip reef shark (Carcharhinus melanopterus) and the spinner shark (Carcharhinus brevipinna). Let’s compare each one in turn and see just how easy it can be to misidentify them.
The Blacktip Reef Shark V. The Blacktip Shark
Both are members of the Carcharhinidae family, however the blacktip shark is a larger bodied shark than the blacktip reef shark. While both species do have characteristic black caudual and pectoral fin tips, the blacktip reef shark has the white band that highlights these band marks, as well as the black dorsal tips. The blacktip shark lacks the dorsal fin markings (Tricas, et al., 1997). Both sharks exhibit counter-shading camouflage, where the top of the shark shaded grey or brown grey, and the belly of the shark is white. This helps the shark blend with the surrounding water column when looking down on the shark from above, or looking up at the shark from underneath (Parker, 2008). The blacktip reef shark is only found in the warm temperate and tropical waters of the Indian and Pacific Oceans, and in the Eastern Mediterranean via the Suez Canal. The blacktip shark has a much wider home range. It can be found worldwide in warm temperate and tropical waters in many of the same reef and lagoon habitats as the blacktip reef shark (Burgess, & Branstetter, 2009). Due to all of their similarities and overlapping habitat preferences, these two species can cause some confusion when trying to identify species.
The Spinner Shark V. The Blacktip Shark
These two species share the same home range, as well as the same inshore habitat preference. They also have strikingly similar body structures and black tip markings. However, the blacktip shark does not have a black tip on the anal fin, while the spinner shark has black tips on all fins. The spinner shark also has the first dorsal fin slightly further on the back than the blacktip shark. However, the similarities are so similar that it is likely landings data for the spinner shark are reported as a blacktip shark (Burgess, 2009).
So can you spot the differences between the three?
The blacktip shark is currently categorized as a Near Threatened species by the International Union for the Conservation of Nature (IUCN). They are directly targeted by recreational and commercial fisheries in the United States and the Gulf of Mexico (Branstetter, & Burgess,1996; Branstetter, & Burgess, 1997). They are a commonly caught species in Indian fisheries and the driftnet fishery in the Mediterranean, as well as a minor component of the shark catch in Australia (Last & Stevens, 2009). When they are caught for commercial purposes, the majority of the shark is utilized. Their hides and skins are used to make leathers. Oils from their livers are extracted in some regions for cosmetics and pharmaceuticals. Their meat can be consumed by humans and it is typically sold within local regions. Their fins are dried before shipping to the East for the fin trade (Burgess & Branstetter, 2009). However, despite being commercially valuable, there is evidence to suggest that their populations along the eastern coast of the United States have been declining over recent years. In the longest continuous survey of sharks conducted annually since 1977 off the coast of North Carolina, blacktip shark populations had declined by over 90%, along with many other large shark populations (Klimley, 2013). Their populations were considered overfished. Currently, the fishing of blacktips is managed within the United States and Australia through management plans which collectively addresses the entire group of species represented in the fishery (Burgess & Branstetter, 2009). Continued monitoring of the species throughout its region is needed to assess further population decline and needed conservation actions.
Authority: Müller and Henle, 1839
Family: Carcharhinidae; 59+ species
Length: 8.3 feet (2.55 m)
Weight: Up to 150 lbs (68 kg)
Habitat: Continental and insular slopes, usually close to shore; can tolerate reduced salinity
Depth: Rarely deeper than 98 feet (30 m)
Reproduction: Placental Viviparity
Gestation: 11 – 12 months with 1 year between pregnancies
Litter Range: 4 – 11 pups
Home Range: Globally widespread in the tropics and subtropics
Diet: Small schooling fishes like sardines and anchovies, as well as crustaceans and squids
IUCN Status: Near Threatened
(Tricas, et al., 1997; Burgess & Branstetter, 2009; Ebert, Fowler, & Dando, 2015; Skomal, 2016)
The new Ocean For Sharks Shop is open! There’s handmade ocean inspired plush animals, canvas paintings, and of course my children’s book, Winifred the Wondrous Whale Shark, available in print and PDF. Be sure to stop by. Proceeds benefit shark research and conservation with a donation to Project AWARE!
Thanks so much for checking out the Blacktip Shark! If you missed last week’s featured species, please be sure to check out the bearded Tasslled Wobbegong! If there is a species of elasmobranch you’d love to know more about, leave me a comment or send me a message! I would love to do a feature on your favorite species. Also connect with me on Instagram and Facebook for even more elasmo fun!
Conservation legislation needs public support in order to become law and help protect the environment and wildlife. Tell your representatives that you care about environmental and wildlife conservation. It only takes a moment to make a change that will last a lifetime. Until next time finactics!
Featured Image Source
Perrine, D. (Photographer). (2017). Blacktip shark (Carcharhinus limbatus) underwater [Digital Image]. Retrieved from https://www.floridamuseum.ufl.edu/
Bigelow, H. B., & Schroeder, W. C. (1948). Fishes of the Western North Atlantic: lancelets, cyclostomes, sharks. Sears Foundation for Marine Research, Yale University.
Branstetter, S., & Burgess, G. H. (1996). Commercial shark fishery observer program. Characterization and comparisons of the directed commercial shark fishery in the eastern Gulf of Mexico and off North Carolina through an observer program. Final Report, MARFIN Award NA47FF0008, 33pp, 11.
Branstetter, S., & Burgess, G. H. (1997). Commercial shark fishery observer program 1996. Tampa: Gulf and South Atlantic Fisheries Development Program.
Burgess, G.H. (2009). Carcharhinus brevipinna. The IUCN Red List of Threatened Species. Retrieved from https://www.iucnredlist.org/species/39368/10182758
Burgess, H. G. & Branstetter, S. (2009). Carcharhinus limbatus. The IUCN Red List of Threatened Species. Retrieved from https://www.iucnredlist.org/species/3851/10124862
Ebert, D. A., Fowler, S. L., & Dando, M. (2015). Sharks of the world: a fully illustrated guide. Wild Nature Press.
Huber, D. R., Weggelaar, C. L., & Motta, P. J. (2006). Scaling of bite force in the blacktip shark Carcharhinus limbatus. Zoology, 109(2), 109-119.
Klimley, A. P. (2013). The biology of sharks and rays. University of Chicago Press.
Last, P. R., & Stevens, J. D. (2009). Sharks and rays of Australia. 2nd Edit.
Parker, S. (2008). The encyclopedia of sharks (2nd ed.). Buffalo, NY: Firefly Books Ltd.
Skomal, G. (2016). The Shark Handbook: The Essential Guide for Understanding the Sharks of the World. (2nd ed.). Kennebunkport, ME: Cider Mill Press.
Tricas, T. C., Deacon, K., Last, P., McCosker, J. E., Walker, T. I., & Taylor, L. (1997). The Nature Company Guides: Sharks and Rays. (L. Taylor, Ed.). Hong Kong: The Nature Company, Time Life Books.