Bull sharks – salinity tolerance little-studied despite river attacks
While putting together a presentation for a Marine Biology subject on lionfish (and throwing in the recent controversy over plagiarised lionfish research), I struggled to find much research on an equivalent marine creature that has developed the same low salinity tolerance.
There were papers on the more well-known euryhaline species (those that tolerate wide ranges of salinities) but surprisingly little on bull sharks (Carcharhinus leucas) and their emergence as key predators in northern Australian rivers and lakes. This is strange given the heavy reporting on shark attacks far upstream in the Brisbane Times, Courier Mail and ABC TV among others.
Juvenile bull sharks have even been found in golf course lakes and unconfirmed reports stated there have been sightings in the Wivenhoe Dam. From what I could find in my research, freshwater bull sharks had a less-developed rectal gland (along with kidnyes, responsible for salt excretion) than their marine cousins and adults were less likely to shift back into marine waters from their freshwater range.
As for competition with longer-term inhabitants of the region: