Welcome to this week’s Featured Species: The Bronze Whaler also known as the Copper Shark (Carcharhinus brachyurus). This absolutely stunning shark is named for its lustrous skin that shines a reddish-copper color (Tricas et al, 1997). The bronze whaler is a large, slender shark with a rounded, narrow snout. Besides the copper color of their skin along their backs, they have a stark white belly in contrast and a short band of pale pigmentation that runs laterally between the pectoral and anal fins (Tricas et al, 1997). Some individuals have dark tips on their pectoral fins, but this is not observed on every individual.
Despite their flashy copper skin, the bronze whaler is often mistaken for their cousin the dusky shark (Carcharhinus obscurus) when conducting underwater surveys (Duffy & Gordon, 2003). The reason for this has to do with the physics of light when it travels through water. The white light that we see is actually made of a spectrum of color. We perceive color when an object absorbs all the other colors and reflects back to our eyes the color we see. So the reddish skin of the bronze whaler shark is absorbing all the other light but reflecting back what we see as the reddish-copper color. With me so far?! Great! Now each color has a wavelength or a different level of energy. Reds have a low energy, so their wavelengths are very long and far apart. Blues have a very high energy and their wavelengths are very close together. Picture two friends holding a sheet between them. So when light enters a medium other than air, say ocean water for example, the low energy red wavelength is slowed down even further. It has more resistance and loses energy the further down it travels (Parker, 2008). When we are diving, we lose the red spectrum of light relatively close to the surface. So as the bronze whaler shark dives below the surface, its spectacular color is also lost and begins to look gray or brown. This can lead to mis-identification of the species when conducting surveys (Duffy & Gordon, 2003). Check out this video to see how quickly color changes when diving underwater!
Kendall Roberg (Videographer). (2016 July 5). Underwater Color Loss With GoPro 0 to 155 Feet Depth – Fishing Lure Deep Test [Video Clip]. Retrieved from https://www.youtube.com/
The bronze whaler shark is a coastal shark. It can live in brackish waters near the mouths of rivers and estuaries, but it is also found offshore in deeper waters near reef shelves in the tropics and subtropics (Fowler, 2002). Juveniles typically spend their first few years in shallow coastal waters of protected nursery habitats before moving into deeper waters as subadults (Smale, 1991). During this time, the juveniles hone their hunting skills by going after a variety of small bony fishes and invertebrates (Tricas et al, 1997). Adult males are present in subtropic regions year round, however females perform seasonal migrations to mate and pup. Females migrate to the subtropics during the winter months to mate. After a year of gestation, in the following spring, females return to temperate inshore regions where they pup (Cliff & Dudley, 1992).
Like most species of elasmobranchs, the bronze whaler is a meso-predator, or a mid level predator. These predators are more generalized than apex predators like the great white shark (Carcharodon carcharias). Meso-predators have a lot of variation in their diets. The bronze whaler is known to eat invertebrates, a great number of bony fishes, and even other elasmobranchs (Tricas et al, 1997; Duffy & Gordon, 2003). To accommodate such an appetite, the bronze whaler as an upper jaw with serrated teeth with rounded leading edges that are made for tearing and cutting. The lower jaw has slimmer, triangular teeth that are meant for piercing and holding prey (Tricas et al., 1997).
The bronze whaler is one of the few species of shark that has been observed hunting cooperatively. As adults, they are known to form schools for a sole purpose of hunting together. The sharks will spread out to surround a school of fish and swim inward from all directions, forcing the school into a tighter and tighter ball. Once the bait ball is formed, the sharks charge in and pick off the prey a bite at a time until there is nothing left of the school. The co-op of sharks then dissolves and the sharks go their separate ways (Parker, 208).
NatureFootage (Videographer). (2018 September 5). Sardine Run Bait Ball with Gannetts, Common Dolphin, and Copper Sharks (Bronze Whaler) [Video Clip]. Retrieved from https://www.youtube.com/
Authority: Günther, 1870
Family: Carcharhinidae; 59+ species
Length: 7.5 feet (2.3 m)
Weight: 370 lbs (168 kg)
Habitat: Coastal waters; brackish and freshwater river mouths and estuaries, continental slopes and shelves
Depth: Surface to 330 feet (100 m)
Gestation: Suspected between 12 to 21 months
Litter Range: 7 – 24 pups
Home Range: Global population distribution in coastal temperate and subtropical waters
Diet: Wide variety of bony fishes, other elasmobranchs, and some invertebrates
IUCN Status: Near Threatened
(Trica et al, 1997; Stevens, 1997; Duffy & Gordon, 2003)
Thanks so much for checking out this week’s brilliant Bronze Whaler! If you missed last week’s featured species, don’t miss the walking Epaulette Shark. If there is a species of shark 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.
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Featured Image Source
Tresfon, J. (Photographer). (2012). Carcharhinus brachyurus in Sardines [Digital Image]. Retrieved from https://skaphandrus.com/pt/fotografia-subaquatica/fotografia/16038-Sardines-%2858%29
Chiaramonte, G. E. (1998). The shark genus Carcharhinus Blainville, 1816 (Chondrichthyes: Carcharhinidae) in argentine waters. Marine and Freshwater Research, 49(7), 747-752.
Cliff, G., & Dudley, S. F. J. (1992). Sharks caught in the protective gill nets off Natal, South Africa. 6. The copper shark Carcharhinus brachyurus (Günther). South African Journal of Marine Science, 12(1), 663-674.
Duffy, C. & Gordon, I. (2003). Carcharhinus brachyurus. The IUCN red list of threatened species. Retrieved from https://www.iucnredlist.org/species/41741/10551730#habitat-ecology
Fowler, S. L., Reed, T. M., & Dipper, F. (Eds.). (2002). Elasmobranch Biodiversity, Conservation and Management: Proceedings of the International Seminar and Workshop, Sabah, Malaysia, July 1997 (No. 25). IUCN.
Parker, S. (2008). The encyclopedia of sharks (2nd ed.). Buffalo, NY: Firefly Books Ltd.
Smale, M. J. (1991). Occurrence and feeding of three shark species, Carcharhinus brachyurus, C. obscurus and Sphyrna zygaena, on the Eastern Cape coast of South Africa. South African Journal of Marine Science, 11(1), 31-42.
Stevens, J. D. (Ed.). (1997). Sharks (6th ed.). New York: Facts on File.
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.