33.Which populations are in reserve systems? Which of these are actively managed for this species? Give details.
No species-specific mechanisms are currently in place to manage particular populations of C. leucas, though sharks in general may be afforded some protection in reserve areas; however specific details regarding populations that remain within MPAs are not available.
In Australian waters, C. leucas is likely found within Marine Protected Areas in the species range,occurring either permanently or occasionally.
The map below shows the Commonwealth marine protected areas as of 2009 (source: DEWHA).
Image deleted due to copyright requirements
Habitat
34. Describe the species’habitat (e.g. aspect, topography, substrate, climate, forest type, associated species, sympatric species). If the species uses different habitats for different activities (e.g. breeding, feeding, roosting, dispersing, basking), then describe each habitat.
C. leucas inhabits a broad range of aquatic environments. These range from shallow marine environments of depths of 1m to depths of 150m, and due to the specie’s euryhaline physiology it also has the capacity to survive indefinitely in estuarine and completely freshwater river and lake environments. It is found within waters of both very high and low turbidity.
The species is known to be migratory in its habits, with pregnant females migrating to estuarine areas to give birth. The juveniles remain in these areas until temperatures drop below optimal levels when they migrate to warmer offshore waters. (Simpfendorfer & Burgess, 2005). Simpfendorfer and Burgess (2005) also reported on a study in the US which demonstrated the migratory behaviour of C. leucas along the east coast, moving northwards during summer as temperatures rise and southwards as temperatures in the north cooled.
The behaviour of adult bull sharks appears to vary across their range. Most authors report observations that adults have a relatively sedentary lifestyle – although there is an ontogenic partition and movement between environments relating to age categories, adults rarely move far from the surrounding waters of the estuaries they developed in (Wintner et al, 2002).
In general, adults use estuarine environments with mid-range salinity values as nursery grounds (McCord and Lamberth, 2009; O’Connell et al, 2007), including man-made canal systems (Green et al, 2009; Heupel and Simpfendorfer, 2008). Juvenile C. leucas usually remain within low salinity estuarine environments, surmised to be advantageous due to lower risk of predation.
35. Does the species use refuge habitat, e.g. in times of fire, drought or flood? Describe this habitat.
As an active swimmer, C. leucas is likely capable of retreating to zones of lesser impacted coastal water in times of flood or storm.
36.Is the extent or quality of the species’ habitat in decline? If the species uses different habitats, specify which of these are in decline.
Due to the proximity of human development with C. leucas’preferred habitat, it is likely that significant portions of C. leucas’habitats, particularly riverine and estuarine systems but also marine environments, have suffered a decline in quality (Cavanagh et al, 2003). This decline is primarily due to anthropogenic habitat modification and pollution through agriculture and industry.
37. Is the species part of, or does it rely on, a listed threatened ecological community? Is it associated with any other listed threatened species?
C. leucasis not solely part of, and does not rely solely on, a listed threatened ecological community. However as an opportunistic predator C. leucas likely interacts with listed threatened species as part of a balanced ecosystem. The nominees are not aware of specific examples have that have been published.
Feeding
38.Summarize the species’ food items or sources and timing/seasonality.
C. leucas is an opportunistic eurytrophic predator (Thorburn, 2006). Although preferring bony fish and other elasmobranches as prey, C. leucas is omnivorous and has been known to consume turtles, birds, terrestrial and aquatic mammals including dolphins, crustaceans, molluscs and echinoderms, as well as carrion (Last and Stevens, 2009). Snelson et al (1984) observed that analysis of stomach contents of C. leucasshowedselectivity for the most common food items present, usually bony fish species. A greater dependence on elasmobranch prey has been correlated with increased size (Cliff and Dudly, 1991). There is no data available on seasonality of dietary preference.
39.Briefly describe the species’ feeding behaviours, including those that may make the species vulnerable to a threatening process.
C. leucas is an aggressive and inquisitive feeder that relies on visual, electrochemical and olfactory cues to locate prey. The species’ willingness to undertake exploratory feeding behaviour on a wide variety of organisms, including rare instances of humans, leads to this species being particularly maligned, and hence targeted by retaliatory fishing effort. It’s easily accessed habitat and low selectivity of food items makes this species vulnerable to such concerted hunting efforts.
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