Bull sharks also inhabit many estuaries and rivers in the countries listed above. These estuaries are used as nurseries for the young sharks. Many juvenile sharks have been found in areas in southwest Florida, such as the Indian River Lagoon System, Charlotte Harbor, Caloosahatchee River, San Carlos Bay, and the lower Pine Island sound. (Castro, 2011; Jenson, 1976; Simpfendorfer, et al., 2005)
Bull sharks are located in tropical and subtropical bodies of water. They spend their time in a depth of around 30, but can exist at depths up to 150m near the coast. They occasionally occupy rivers (average depth of just 2.4m) and lakes. They can also be found in ocean inlets where saltwater meets freshwater, and are the only shark species that can tolerate prolonged periods in freshwater environments. Bull sharks will give birth in estuaries and their young will use the environment as a nursery. The young will remain in this estuary until temperatures drop seasonally, and the young move to the saltwater environs. ("Carcharhinus leucas", 2009; Curtis, et al., 2011; Ortega, et al., 2009; Simpfendorfer, et al., 2005)
Bull sharks are sexually dimorphic, with females larger than males. At birth, bull sharks weigh 1.5-3.0kg and are approximately 60-71cm. Immature females average 189cm and immature males are around 193cm with both weighing around 53kg. When they reach adulthood (age 18), females weigh 111kg and are approximately 242cm. Males reach adulthood at age 14, weighing 95kg and averaging 228cm in length. ("Carcharhinus leucas", 2009; Castro, 2011; Clark and von Schmidt, 1965; Snelson, et al., 1984)
Bull sharks have very short snouts and the adults are a light to dark gray on the dorsal side and white on the ventral side. Juveniles are a brownish gray color and have black tips on the pelvic, second dorsal, anal, and tail fins. Bull sharks teeth are a broad jagged triangle up top and a thin jagged triangle along the jawline. The shark’s placoid scales are overlapping, sharp, pointed triangles that effectively protect them. These scales are thought to be hydrodynamic and assist with efficient swimming. (Castro, 2011; Clark and von Schmidt, 1965)
Adult size does vary depending on geographical region. For example, North American bull sharks are larger than those located in the Caribbean, Costa Rica, or Nicaragua. Females in North America are an average of 284cm and males are an average of 270cm. Alternately, the largest female shark found in Costa Rica measured 251cm and the largest male was 241cm. ("Carcharhinus leucas", 2009; Castro, 1996; Clark and von Schmidt, 1965; Snelson, et al., 1984)
Growth rate is fast in young sharks, and slowly decreases throughout the shark's life. Growth was estimated at 18 cm in the shark's first year of life and 16 cm in the second year. Subsequently, they grow about 11-12cm a year, slowly dropping to 9-10cm per year. Female bull sharks are estimated to reach reproductive maturity around the age of 18 and males are estimated to reach maturity at age of 14-15. It is estimated that bull sharks can grow up to 340cm, and that this growth is indeterminate. ("Carcharhinus leucas", 2009; Gilbert and Schlernitzauer, 1966; Simpfendorfer, et al., 2005; Wourms, 1981)
There is not much information about Carcharhinus melanopterus and Carcharias taurus females illustrate their readiness to mate by reducing their speed and swimming with their tails in a more upward position and their snout pointing slightly down. The male will then come up to the female and place its snout below the female’s vent. (Economakis and Lobel, 1998; Gordon, 1993)mating behaviors, except that they are polygynandrous. Within this genus,
Males have the tendency to bite during copulation and therefore females often receive mating scars. Researchers have found that females have bite marks located on the pectoral and pelvic fins and very rarely near the head. Males are very rarely marked. (Pratt and Carrier, 2001)
Female bull sharks have one right active ovary that extends to the abdominal cavity. Usually 15 to 22 eggs are enlarged in the ovary; however, 10 or fewer undergo ovulation. The eggs that do not undergo ovulation are reabsorbed. Immature eggs are around 1-2mm and those that mature are about 4-5cm. (Jenson, 1976)
This species is viviparous meaning that the shark sustains their young through a yolk-sac placenta. The female’s age can determine the size and shape of the oviducts. An immature female will have the same width throughout the oviduct and in general is very narrow. A mature female’s oviduct will be thicker towards the end of the oviducts and have more flexibility. (Jenson, 1976)
Gestation usually lasts 10-11 months and parturition occurs from April - June in most of its range. In tropical waters, they are known the breed year-round. Towards the end of term, the embryos are around 50-75cm long and are contained in elongated sections. They are born tail first. In order to contain all the eggs the uterine walls are stretched and very thin. After pregnancy, the uterine walls increase in thickness and decrease in size. Given the long gestation period, these bull sharks will reproduce every other year. ("Carcharhinus leucas", 2009; Jenson, 1976)
For males, both the gonads are of equal size and shape. Both are functional. Immature gonads are very small and barely distinguishable. Mature gonads are larger and contain more vessels. Claspers of (Jenson, 1976)are thicker towards the base and thinner towards the tip.
Male bull sharks are sexually mature around 160-165cm. This is partly determined by the size of their claspers. Female sharks mature around the size of 160-170cm. This is partly determined by the size and condition of the reproductive organs. Males mature around the age of 14-15 years old and females mature at ca. 18 years. ("Carcharhinus leucas", 2009; Jenson, 1976)
There is not much known about the parental investment in sharks. However bull sharks use nursery areas in estuaries in order to provide protection for their young. The young have more opportunities to stay safe from predators and have greater food supply in these nurseries. This facilitates a greater survival rate and presumably more rapid growth. (Simpfendorfer, et al., 2005)
Bull shark longevity appears to be related to geographic region. Studies of bull sharks in the southern Gulf of Mexico indicate that they can reach an age of 28 years for females and 23 years for males. In the northern Gulf researchers found that female bull sharks live to be 24.2 years and the oldest male was 21.3 years. Researchers also found a female bull shark off the eastern coast of South Africa that was 32 years. (Castro, 1996; Cruz-Martinez, et al., 2004)
Two bull sharks housed at the South African aquarium were known to be 29 years old. Another bull shark was located at the Okinawa Churaumi Aquarium lived to be 30 years old. (Castro, 2011)
Members of the genus Carcharhinus are considered very aggressive. Bull sharks are known to be so violent that many aquariums do not display them; they tend to kill everything in their environment. A study was conducted that studied the attack behavior of Carcharhinus amblyrhynchos. The sharks’ body starts to move in a spinning and winding motion. At the same time, its body moves in a back and forth motion. They swim in an almost disoriented way instead of a fluid motion. Their path of motion is in a circular pattern, with their snout pointing upward. It is thought that bull shark attacks may follow similar behavioral patterns. This is sometimes a seasonally migratory species - for those bull sharks inhabiting the east coast of the United States, they will spend summers in northern latitudes and move southward again when waters cool. Sharks behavior may also vary according to habitat type. For example, sharks are active throughout the daytime in riverine systems, moving upstream. Their nocturnal behavior returns them to their start point, returning downstream. Habitat choice in this species also seems to be linked to water temperature, and sharks will vacate cooler temperate waters when they are no longer optimal. ("Carcharhinus leucas", 2009; Castro, 2011; Johnson and Nelson, 1973; Simpfendorfer, et al., 2005)
Bull sharks' linear home ranges vary from 0.9-5.6km in rivers. They spend their day moving upstream and swim near the bottom of the river. At night they move downstream and swim at the top of the river. They spend a large amount of time in backwater habitats and estuaries. Home ranges in oceanic environments have not been documented. (Heupel, et al., 2010; Yeiser, et al., 2008)
Bull sharks have a keen sense of hearing. They are very efficient at detecting sound between 400-600 Hz but could hear frequencies between 100-1500 Hz. This capability helps sharks detect potential prey at distances over 6 m (20ft) away. Although no studies have quantified the bull shark sense of smell, researchers presume that it is as strong as other sharks in the same genus. Reports on species within Carcharhinus indicate the use of their olfactory system to detect the opposite sex. Scientists suggest these sharks release a pheromone and the olfactory system is capable of identifying the smell. (Johnson and Nelson, 1978; Nelson, 1967)
Bull shark diet commonly consists of Ariidae catfish such as Ariopsis felis and Bagre marinus. They also commonly eat stingrays such as Dasyatis sabina and D. sayi. Their diet can sometimes contain Callinectes, Brevoortia, and Mugil. Bull sharks rarely eat Archosargus probatocephalus, members of the family Carangidae, Cynoscion, and even members of their own species.
There is a general pattern of the shark’s diet as they mature. In the younger stages, they feed on fish that are ray-finned. Then as they age they start to consume other elasmobranchs. They also prey on fish near the bottom of the oceanic coastal regions.
Bull sharks' minor prey consists of smaller mammals, birds, mollusks, crustaceans, and even turtles. Incidents have occurred where bull sharks have committed cannibalism. This usually occurs when there are at least six sharks present and one of the sharks is injured. (Cliff and Dudley, 1991; Snelson, et al., 1984; Vorenberg, 1962)
Bull sharks are at the top of the food chain and have very few predators. This species is rarely cannibalistic, targeting smaller sharks and injured sharks. Bull sharks are susceptible prey to larger sharks. Humans Homo sapiens are also known to catch and kill them for their fins and flesh. (Castro, 2011; Economakis and Lobel, 1998; Snelson, et al., 1984)
A mutual relationship occurs between bull sharks and the remora Labroides dimidiatus. If the shark is infected with parasites it will change its behavior so that the remora will know that it is ready to be cleaned. The shark will slow down its swimming speed and swim with its head raised. The remora will then approach and clean all around the shark’s body, gills, and inside the mouth. The remora benefits because it receives food and the shark benefits because it gets rid of the unwanted parasites. (Keyes, 1982)
Some bull sharks are susceptible to obtaining tapeworms from the trypanorhynch family. This parasite, Heteronybelinia estgmena, is located within the shark’s gastrointestinal tracts. The parasite can cause major inflammation and lymphofollicular hyperplasia. (Borucinska and Caira, 2006)
Bull sharks are sometimes used in aquaria. Many choose not to display them because they consume all of the other fish in the tank. However, this species is still in demand, as it adapts fairly well to life in a tank. Its aggressive nature is apparently a source of amusement for the public. ("Carcharhinus leucas", 2009; Castro, 2011; Simpfendorfer, et al., 2005)
Bull sharks are sometimes caught for sport, and are also accidental captures. Only one study (Gulf of Mexico) examined the capture of bull sharks in commercial nets. In this 1978 research, bull sharks comprised 11% of the biomass catch for sharks.
Bull sharks' body parts are in high demand. People sell their liver oil, meat, and skin. The liver oil is used to make beauty products. Shark meat is mostly sold in European countries. Sharkskin is sold to use as leather. Their fins are the most popular product being traded. Shark fins are used to make traditional Chinese shark fin soup. ("Carcharhinus leucas", 2009; "From head to tail", 2008)
Because these sharks reside in shallow coastal waters, they are known to attack humans. They are a very aggressive species and sometimes mistake humans for large prey. They are known to investigate boats in rivers and estuaries. This behavior suggests they are constantly foraging for food and might mistake boats or humans for food. (Castro, 2011; McCord and Lamberth, 2009)
Recent studies suggest that there has been a decline in bull sharks in estuary habitats. This is based on a measured decline in accidental captures of sharks in gillnets and beach seines from 1953-2003. The IUCN Red List considers bull sharks to be nearly threatened. This presumed decline could be due to the increase of human development in coastal waters and shorelines. Because bull sharks’ nurseries tend to be in shallow estuaries, this development could be affecting the population. Several states in the southern U.S. have eliminated the use of gill nets in potential nursery areas, so it's presumed that these actions have indirectly helped the bull shark. ("Carcharhinus leucas", 2009; O'Connell, et al., 2007; Simpfendorfer, et al., 2005)
Kristi Cascio (author), Radford University, Karen Powers (editor), Radford University, Tanya Dewey (editor), University of Michigan-Ann Arbor.
the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.
Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
living in the southern part of the New World. In other words, Central and South America.
body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.
uses sound to communicate
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
areas with salty water, usually in coastal marshes and estuaries.
an animal that mainly eats meat
uses smells or other chemicals to communicate
the nearshore aquatic habitats near a coast, or shoreline.
humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.
uses electric signals to communicate
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.
union of egg and spermatozoan
A substance that provides both nutrients and energy to a living thing.
mainly lives in water that is not salty.
Animals with indeterminate growth continue to grow throughout their lives.
fertilization takes place within the female's body
the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.
referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
makes seasonal movements between breeding and wintering grounds
having the capacity to move from one place to another.
specialized for swimming
the area in which the animal is naturally found, the region in which it is endemic.
active during the night
generally wanders from place to place, usually within a well-defined range.
found in the oriental region of the world. In other words, India and southeast Asia.
chemicals released into air or water that are detected by and responded to by other animals of the same species
an animal that mainly eats fish
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.
mainly lives in oceans, seas, or other bodies of salt water.
reproduction that includes combining the genetic contribution of two individuals, a male and a female
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
movements of a hard surface that are produced by animals as signals to others
uses sight to communicate
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
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