A new study published in the journal Marine Ecology Progress Series by researchers from the University of Miami underscores how declining shark populations in our oceans might impact fish’ bodily features in a particular environment.

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The researchers reached this conclusion after sampling more than 600 fish from two coral reef systems off the coast of Australia. One, dubbed Rowley Shoals, has more sharks swimming around. The other, known as Scott Reefs, doesn’t have as many because of over-fishing issues.

As it would seem, the fish from Scott Reefs sported smaller eyes and fins than those found in the shark-infested waters of Rowley Shoals. Scott Reefs-based fish exhibited eyes that were up to 46% smaller than those from Rowley Shoals, and fins were up to 40% smaller. A mere coincidence? Researchers don’t think so.

"Eye size is critical for detecting predators, especially under low-light conditions when many sharks usually hunt, and tail shape enables burst speed and rapid escape from sharks," noted study lead author Neil Hammerschlag from the University of Miami.

"Our results suggest that removals of sharks by humans have potentially caused a reduction in the size of fish body parts that are important for shark detection and evasion."

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Fish rely on their eyes and fins to evade predators. The eyes allow them to survey the surrounding environment for potential threats, while the fins provide an escape plan whenever danger gets too close for comfort.

In waters with fewer natural predators, these reef-based fish don’t need overkill eyesight or larger getaway fins. That said, fish from Scott Reefs might be evolving to suit the changing environment.

"These patterns were consistent across seven fish species that vary in behavior, diet, and trophic-guild," added study co-author Mark Meekan.

"These results are particularly important since sharks are among the most threatened marine animals and the consequences of their global removals due to fishing is not well understood and has been a topic of significant speculation, debate, and concern."

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There isn’t enough data at this point to conclude how these changes might impact the marine ecosystems in the long run, but the researchers warn of potential adverse impacts to the food web as just one example.

Perhaps follow-up studies could discern whether the same traits apply to other marine environments around the world.

Source: University of Miami