Due to the pristine nature of its reef communities, Palau is regarded as one of the world’s best diving locations. Sharks are a vital part of this ecosystem because of their role as predators at the top of the food chain.Growing evidence suggests that reef communities undergo fundamental changes when sharks are removed.
The loss of sharks and other large predators alters the way reef fish assemblages are structured and energy flows, so that reefs with sharks are often characterised by high coral cover and few small fish species (and of course, lots of sharks), while reefs without sharks are typified by great abundances of small fishes and low coral cover. In this case the coral is typically replaced by algae.
Evidence shows how easily sharks can be removed by fishing. Because sharks can live a long time, they have slow growth and take many years to become reproductive. They also have few young. For species such as grey reef sharks, common on reefs in Palau, adults may live to be 25-30 years old, will not become reproductive until they are at least 7 years old and the females may only have 1-5 pups every second year. Such traits are typical of most species and mean that sharks can sustain very little harvesting by a fishery. Even by-catch can endanger populations.
Thus shark fishing is likely to harm the reef ecosystem and reduce the services and benefits that these reefs provide to the people of Palau. This harm will occur due to:
- likely changes in the structure and abundance of reef fish assemblages
- a reduction in the resilience of reefs to other disturbances caused by bleaching and climate change because of the loss of keystone predators
- reduction in the attractiveness of Palau as a destination for dive tourism, since many divers visit specifically to see sharks
The Domino Effect
Excert from; Ongoing Collapse of Coral Reef Shark Populations by Robbins, Hisano, Choat, James Cook University.
"Reef sharks are strongly interacting apex predators. Loss of this group has a large implication for marine trophodynamics. On coral reefs, food-web models indicate that trophic cascades initiated by shark overfishing may have contributed to the collapse of Caribbean coral-reef ecosystems.
Sharks are the top predators in the ocean
Reef fish are feeding on smaller fish and corals
What will happen to these ecosystem when top predators disappear?
More bigger reef fish, less smaller fish, algae growth on the corals, corals die, collapse of ecosystem."