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Shark's Role in the Ecosystem


As apex or top level predators, sharks sit atop the food chain and with no natural enemies, shark numbers are designed to be low. Sharks feed on an extremely wide range of prey items with very different methods. Some sharks such as the whale shark (Rhincodon typus) and the megamouth shark (Megachasma pelagios), are filter feeders. They move through the water with their mouths wide open and let water, filled with plankton, flow through their mouths and gill-rakers, where they sieve out the plankton. At the other end of the feeding scale are the great white shark (Carcharadon carcharias) and the broadnose sevengill shark (Notorynchus cepedianus) that feed on a range of invertebrates and vertebrates, including a high number of marine mammals.


When top level predators are removed this can cause a ‘topdown’ effect on organisms lower in the food chain. This has been clearly demonstrated in some parts of the oceans where a predator’s population was reduced so much that the population of the main prey began to explode. Because there were then so many of the prey they began to eat themselves out of food, changing the ecology of the whole area.


Healthy shark populations ensure the future survival of many fish, corals and marine species which would otherwise be decimated by population explosions of the more numerous and faster breeding smaller predators.


In addition to their ecological importance as apex predators in our oceans, sharks are being subjected to intense fishing pressure worldwide as a result of the high demand for shark fins and cartilage. Since many sharks travel long distances, crossing oceans and national boundaries, they are susceptible to the unregulated fishing efforts of multiple nations. Consequently, shark populations have plummeted worldwide to less than 30 percent of their numbers two decades ago. This decline, coupled with the slow reproductive rate of most sharks has prompted great concern about the health of shark populations and an urgent need for effective conservation and management.

Shark populations worldwide are declining at an alarming rate. Research indicates that we may see several shark species extinct within our lifetime.