True to its namesake, Shark Bay has a large number and diversity of sharks. From the small black-tipped sharks to the 5m tiger shark, Shark Bay is home to more than a dozen shark species. The tiger shark, Galeocerdo cuvier, is the most common shark in the bay and has been the subject of intensive study by Mike Heithaus (Florida International University). They have found, using the “crittercam” developed by Greg Marshall at National Geographic, that tiger sharks hunt in deep and shallow habitats, but most of their prey is in shallow water (4-5m).
Studies of their stomach contents by Australian scientist Colin Simpfendorfer, indicate that seasnakes, turtles, and dugongs are the main prey of tiger sharks, but dolphins have been found in tiger shark stomachs at other sites. Over 74% of Shark Bay dolphins bear shark bite scars of varying size, which is much higher than reports for other populations, but this does not mean that sharks are the main cause of dolphin mortality. Both dolphins and sharks like to forage in the shallow seagrass beds where prey density is the highest, but during the warm months when shark density peaks, dolphins switch to resting in deep water and venturing into shallow habitats in larger groups, suggesting that they are seeking to minimize the threat of shark predation.
Researchers commonly see sharks and dolphins in the same area, and the reactions of sharks to dolphins and dolphins to sharks seems to depend on the size and number of sharks, the size and number of dolphins, and probably some element of surprise. We know that sharks sometimes eat dolphins but dolphins occasionally turn the tables. Researchers have seen sharks chase dolphins and dolphins chase or even mob sharks. Dolphin mothers sometimes chase small (1m) sharks from their young calves. Clearly the relationship between sharks and dolphins is complex and deserving of further study.