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Why Do Smaller Fishes Fear Sharks But Not Humans?

Last updated March 14, 2022| Diving

Scotch has been a target of shark fishermen in Indonesia for centuries. Rowley Shoals has been protectING as a marine reserve since the early 1990s. Now, in a new study, Neil Hammerslag, a marine ecologist at the University of Miami, and his colleagues have shown how the near-extinction of sharks from Scott Reef has sent several subtle changes across the ecosystem.

In Scott Reef, fish that once preyed on sharks now have smaller tails and eyes than the species found in the Rowley Shoals. Hammerslag says the reason is simple: Scotch reefs are no longer important for spotting sharks. Finding out how the removal of the predator affects their prey as far as their DNA is concerned. Hammerslag and his contemporaries concluded after collecting fish from seven prey species from the two reefs between 2012 and 2014. Overall, the researchers analyzed digital images of 611 fish and compared their body dimensions.

small fish

The large-eyed fish informing predators help them crawl on, and the large tails help them swim faster. But Hammerslag says that having these things requires energy. Fish consume more resources to build larger eyes and tails and to move those heavy tails around. If these traits help a fish avoid sharks and survive another day, the cost is worth it. But in shark-less habitats, there are fish with small eyes and tails. The other possible mechanism is called phenotypic plasticity.

Fish may have some degree of flexibility in their genes. If environmentalists tell them that predators are nearby, the fish’s bodies will grow differently. Although the study did not reveal which mechanism works, Hammerslag thinks that natural selection more likely bases on the type of change and their magnitude.

Previous studies have found similar effects of predators on prey in controlled experiments. Even now, other studies on Scott Reef have revealed that the prey fish are fatter and more abundant than the fish in the Rowley Shoals. These changes can affect the organisms that feed on the fish and through the food web.

Do Sharks Hunt People?

As we know, only a dozen of the more than 300 species of sharks implicating in the attack on humans. Further, sharks evolved millions of years before humans existed, so humans are no longer part of their normal diet.


Sharks are opportunistic feeders, but most sharks feed primarily on small fish and invertebrates. Some large sharks prey on special seals, sea lions, and other marine mammals. Also, it is a known factor that sharks attack humans when they are confused or curious. If a shark sees a human being scattering in the water, it can investigate and cause a sudden attack. But sharks should fear more than humans. Sharks hunt for their meat, internal organs, skin, and fins to make products such as shark fin soup, lubricant, and leather.

Especially, sharks are a valuable part of marine ecosystems. But overfishing threatens some shark populations. The NOAA fishing industry researches shark habitats, migration patterns, and population changes to understand how to protect a stable shark population.

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