The frequent use of estuarine and freshwater areas by the Bull Shark makes it more susceptible to deleterious human impacts than species of sharks occurring in other coastal or offshore areas. Bull sharks more frequently encounter humans while in waters of low salinity, and are thereby subjected to increased fishing pressure and environmental changes associated with habitat modification.
Bull Sharks are commonly caught in both commercial and recreational fisheries. Thorson (1982a) reported that a commercial fishery existed for C. leucas in Lake Nicaragua and the Rio San Juan river system in Central America. However, in most situations, Bull Sharks are not normally a fishery target species but are caught as bycatch or as part of a multi-species fishery. For example, in the US Atlantic region they are an important component of inshore ecosystems, but only comprise 1-6% of the large coastal shark catch for this area (Branstetter and Burgess 1997).
While the Bull Shark has been exploited commercially for its skin, liver oil and flesh, currently its fins are the major product driving demand for this and many other species. There are limited data on recreational catches of this species. The best data come from the Gulf of Mexico where Casey and Hoey (1985) reported that in 1978 C. leucas made up about 11% (by weight) of the recreational shark catch of around three million pounds (Casey and Hoey 1985). Recreational catches of large sharks in the Gulf of Mexico have decreased substantially since the 1970s, but Casey and Hoey’s results illustrate that recreational fishing may have a substantial impact on Bull Shark populations.
Beach protection programmes in KwaZulu-Natal, South Africa and Queensland, Australia also regularly catch Bull Sharks. Cliff and Dudley (1992) reported that between 1978 and 1990 the South African programme caught 59 Bull Sharks, 21% of which were released alive. Species identification problems occurred in the Queensland programme until the early 1990s, thus the importance of C. leucas can only be based on data from latter years. Gribble et al. (1998) reported that after identification was improved 16% of the sharks caught state-wide were Bull Sharks, with the majority caught in the central part of the state. The lack of historical data for the Queensland programme and the low abundance in the South African programme make it impossible to assess the impact of beach meshing on Bull Shark populations.
The location of nursery areas in estuarine and freshwater systems makes the species vulnerable to pollution and habitat modification, but there has been only limited study of these impacts on Bull Sharks. Canal developments have been prolific in some estuarine areas where the species is commonly found. It is not known whether these developments have negative impacts. In Florida, USA and the Gold Coast of Queensland, Australia, these developments have substantially altered the environment. Bull Sharks occur frequently in Gold Coast canals and the species has been responsible for a number of attacks on humans (Simpfendorfer unpubl.). The warm water effluent from power stations may also impact this shark. In Florida, USA, juveniles have been reported to be trapped in the warm water outfalls during winter when they would normally have migrated to warmer water areas (Snelson et al. 1984, C. Manire, Center for Shark Research, Mote Marine Laboratory pers. Comm.). The potential impacts of pollution and habitat modification need to be further investigated for this species.