Bull shark, continued 



Movements and Migrations : Movements of sharks to 

 estuarine nursery areas appears to be mainly for 

 parturition (Lineaweaverand Backus 1970). Females 

 move towards whelping grounds in the spring, but do 

 not actually enter them until parturition is eminent. 

 Other movements are probably associated with chang- 

 ing temperatures. Springer (1940) suggested a north 

 and south migration coinciding with spring and fall on 

 the northern Gulf coast. 



Reproduction 



Mode : This species has separate male and female 

 sexes (gonochoristic). The male inseminates the 

 female with the assistance of modified pelvic fins 

 known as clasper organs. Fertilization is internal, and 

 development is viviparous (Castro 1983). 



Mating and Parturition : Descriptions of mating are 

 unavailable due to a lack of detailed observations and 

 reports (Castro 1983). Mating takes place in coastal 

 waters during June and July in the Gulf of Mexico, with 

 pups being born the following year in April, May, and 

 June (Clark and Schmidt 1965). Gestation probably 

 lasts 10 to 11 months (Clark and Schmidt 1965, 

 Branstetter 1981). In warmer waters, mating and 

 parturition can occur year-round (Castro 1983). 



Fecundity : Snelson et al. (1986) took a 249 cm total 

 length (TL) female with 12 near term embryos. Most 

 other investigators report litters of six to eight. 



Growth and Development 



Embryonic Development : Development is viviparous 

 with embryos initially dependent on stored yolk, but 

 later nourished by the mother through a placental 

 connection. Dodrill (1977) proposed that during uter- 

 ine development one or more pups may develop to 

 extraordinary size at the expense of other litter mates. 



Juvenile Size Range : Pups measure around 75 cm at 

 birth (Castro 1983). Size at birth is highly variable 

 ranging from 60 to greater than 75 cm (Branstetter 

 1986, Branstetter and Stiles 1987). Caillouet et al. 

 (1969) showed no significant differences between 

 lengths or weights for male and female neonates 

 shortly after birth. Juvenile weights increased rapidly 

 as maturity approached (Branstetter 1 981 ). Branstetter 

 and Stiles (1 987) estimated growth rates were 1 5 to 20 

 cm/year for the first five years, 1 cm/year for 6 to 1 

 year old sharks, 5 to 7 cm/year for 1 1 to 16 year old 

 sharks and less than 4 to 5 cm/year for sharks older 

 than 16 years. 



Age and Size of Adults : The smallest reported mature 

 male and female are 212 cm TL and 228 cm TL 

 respectively (Branstetter 1981). Males mature at 210- 

 220 cm TL or 1 4 to 1 5 years of age, and females mature 



at >225 cm TL or over 1 8 years of age (Branstetter and 

 Stiles 1987). Females grow larger than males (Clark 

 and Von Schmidt 1965, Branstetter 1986). The bull 

 shark is thought to live to 20 years and possibly longer, 

 and may reach lengths of 2.7 m and weights near 270 

 kg(Shipp1986). 



Food and Feeding 



Trophic Mode : Larvae development is in uterine and 

 nutrients are derived from the mother. At parturition the 

 bull shark is considered a juvenile. Both juveniles and 

 adults are carnivorous predators, but they will also 

 scavenge (Shipp 1986). The bull shark typically feeds 

 during the evening around bridges, passes, and chan- 

 nels. Although usually a sluggish moving fish, it is 

 capable of great speed when pursuing prey (Fischer 

 1978, Shipp 1986). 



Food Items : The bull shark is an opportunistic predator 

 (Lee et al. 1980). Reported stomach contents have 

 included species of loliginid squid and several fishes 

 (longspine porgy, sand perch, striped anchovy, men- 

 haden). Jaws commonly contained spines from rays 

 (Branstetter 1981). Other bony fishes reported from 

 the stomachs of bull sharks are sheepshead, various 

 jacks, common snook, little tunny, hardhead catfish, 

 trunkfish, tarpon, mullets (Clark and Von Schmidt 

 1965); American eel, white perch, Atlantic croaker 

 (Schwartz 1 960), mackerels, tunas, and carrion (Fischer 

 1978). Bull sharks are also known to feed on other 

 sharks, preying heavily on small sandbar sharks, as 

 well as rays, molluscs, sea urchins, crabs, shrimp, 

 porpoises, and sea turtles (Fischer 1978, Lee et al. 

 1 980, Castro 1 983). Snelson et al. (1 984) suggest that 

 saltwater catfishes (hardhead and gafftopsail) and 

 stingrays are very important food items in the diet of bull 

 sharks. This shark is considered to be potentially 

 dangerous to humans. Its habits frequently place it in 

 the vicinity of swimmers and fishermen, and it has been 

 reponsible for several documented attacks (Lee et al. 

 1980, Shipp 1986). 



Biological Interactions 



Predation: The bull shark is not known to be a prey item 

 for other species. 



Factors Influencing Populations : The bull shark is a top 

 trophic level carnivore with slow growth and relatively 

 low reproductive capacity. It is therefore vulnerable to 

 overfishing, and probably should be managed conser- 

 vatively (Casey and Hoey 1 985, NMFS 1 993). A major 

 commercial fishery for these sharks is not recom- 

 mended, and if sport fishing pressures increase there 

 may be need to further regulate the fishery (Casey and 

 Hoey 1 985, NOAA 1 992). Shark mortality also occurs 

 in the form of bycatch from the commercial swordfish, 

 tuna, and shrimp fisheries (NMFS 1 993). The loss and 



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