For whatever reason, sharks have adopted a reputation as human-eating, vicious machines. Ok, so maybe it’s their double rows of many teeth, or large, powerful frame. And yes, movies like Jaws only play into the stereotype. But if we all took a step back to look at the facts, we’d see that this is not the case. In fact, new research in Australia shows that reef sharks have a fairly light diet – and one that has no desire for human flesh.
Scientists at James Cook University’s ARC Centre of Excellence for Coral Reef Studies in Queensland Australia are taking a closer look at the diet of reef sharks to draw further implications on how changes in reef shark populations could alter coral reef ecosystems as a whole. Human hunting and climate change contribute to the numbers of reef shark deaths. The numbers are staggering, as humans kill roughly 100 million sharks per year globally. Decreases in the population of reef sharks is not only detrimental to the species itself, but could also upset coral reef food chains, which could in turn affect coral ecosystems as a whole.
A Reef Shark Study in Australia
Marine biologist Ashley Frisch is the lead researcher on the project in Australia. Her goal is to examine the ecological importance of sharks to coral reefs. Her team first looked at the diet of the sharks, later determining that these reef sharks are not the apex predators on reefs. Their stomach contents revealed a mix of smaller prey, including small fish, crabs, sea snakes, and mollusks. Reef sharks efficient metabolism and opportunistic feeding strategy allows them to consumer smaller prey. By analyzing the stomach contents, the team was able to conclude that reef sharks are mesopredators, or animals in the middle of the food chain, as oppose to apex predators, which exist at the top.
Fisherman kill large numbers of reef sharks, thinking that the sharks will create more competition for the fishermen’s catch. However, little do the fishermen know, the sharks aren’t going after the prize fish the fishermen are targeting.
The interconnectivity of organisms in an ecosystem means that decreases in shark populations could impact a wide variety of species. If we break the food chain down step by step, the impact of dwindling shark numbers becomes much clearer. Say we remove the top level of apex predators – the population of animals on the next level down would most likely increase. Now with this increase at the second level comes a decrease in the next level down from that (more predators would lead to less prey overtime). Following with the trend, the next level down from that would increase. These drastic population alterations within the food chain could dramatically upset the ecosystem as a whole.
Now what do these changes mean for the health of the coral reef? The changes in populations at the top of the food chain will eventually reach the very bottom, even disrupting populations of microscopic plankton – coral’s main source of nourishment. This decrease in the coral’s food source overtime would hurt the health of the coral in the long run.
From Australia to Hawaii
Fortunately, the researchers in Australia aren’t the only scientists who have noticed the mild diet of reef sharks. Marine curators at Maui Ocean Center (MOC) in Hawaii are joining the Australian team to bust the vicious stereotype that these sharks have acquired. The aquarium has a created a program called Shark Dive Maui, where SCUBA-certified guests have the opportunity to dive with reef sharks in the aquarium’s 750,000-gallon Open Ocean Exhibit.
The goal of the program is to expose visitors to reef sharks in a non-violent manner so that they can begin to shift their perception of the shark and recognize what ecological benefits they have to the reef community. According to the aquarium curator, Harry Abrahamsen, “we try to spiritually convey the importance of sharks and the balance they bring to the ocean.”
Both Frisch and Abrahamsen share similar views about reef shark diets. Reef sharks tend to go for the sick and injured fish – favoring the easy catch. Why go for something fast when you could easily capture something moving much more slowly? Frisch noted that many large predators tend to go for injured or weaker animals. This is part of the reason that humans sometimes fall victim to a small nibble. Because we don’t have fins and can’t swim the same way fish do, our limbs dangle in the water and resemble a wounded sea creature, attracting sharks. However, after a curious bite, sharks tend to let humans go. Abrahamsen added to that fact, explaining how the most developed sense a shark has is taste. As a result, a curious shark will bite to assess the object they encounter.
The stomach contents from the Australia study mirrored the facts surrounding reef shark diets. No prey larger than a cheeseburger was found in any of the reef sharks in the study. Additionally, not one stomach analysis revealed any sign of human flesh.
Frisch is hoping that these results “will make people feel a bit safer around reef sharks, because they’re just not a threat to humans.”