Great Barrier Reef Sharks Not Top Predators

By on March 4, 2016
Caribbean reef sharks. (Credit: Greg Grimes via Creative Commons 2.0)

Despite a reputation as the ocean’s top predator, some sharks aren’t such voracious eaters. And indeed some of them aren’t at the top of the food chain but instead occupy more middling parts of chains in the ocean, according to new research out of Australia’s James Cook University.

The find specifically applies to reef sharks inhabiting areas along the Great Barrier Reef. Scientists at the university’s ARC Centre of Excellence for Coral Reef Studies led the study that relied on assessing the stomach contents of reef sharks as well as their tissues. By looking at those two things, it was possible to figure out what the fish were eating in their day-to-day lives.

Instead of chowing down on big fish like groupers or snappers that live along the reef, the results of the analyses revealed that the reef sharks were much more likely to eat smaller prey. These included things like small fish, sea snakes, crabs and even mollusks.

Reef sharks’ diets were similar to that of large reef fish, scientists found. This suggests that reef sharks do not catch big prey. This is likely due to an efficient metabolism and reliance on opportunistic feeding. Such opportunities that reef sharks often take advantage of include attacking sick or injured fish that can’t run away, as well as young fish that are typically smaller in size.

The sharks’ diets also revealed that reef sharks are not apex predators, or animals at the top of the food chain. Instead, they are mesopredators, or animals in the middle of the food chain, which is a far cry from the bloodthirsty perception of great white sharks.

But it is the pervasiveness of this stereotype that is so damaging for the reef sharks. Because reef sharks are seen as competition for fish that Australian fishermen want to catch, like snapper and grouper, the anglers continue to kill the sharks in large numbers.

As reef shark numbers dwindle, the potential implications become clear, researchers say. Because all animals in an ecosystem are connected to one another, a disturbance in reef sharks’ population could have catastrophic effects across the board.

Those effects are pretty clear. If all the apex predators are removed, the populations of animals at the next level tend to increase. Because there’s an overabundance of that second level, there’s a depletion of the next level down and it only continues rippling on from there.

With that in mind, there are pushes to break down anti-shark stereotypes that exist. These include promoting scuba programs, like one at Maui Ocean Center in Hawaii, that let people swim with sharks in a peaceful setting.

Full results of the research are published in the journal Coral Reefs.

Top image: Caribbean reef sharks. (Credit: Greg Grimes via Creative Commons 2.0)

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