The Ocean Blog
Reef Sharks Repelled by People
Reef sharks rarely get any love. These sharks, comprising several species, loiter around coral reefs, snacking on small fish, squids and crustaceans. And while their size is nothing to smirk at -- 5-10 feet is pretty impressive in my book! -- their relatively demure lifestyle just can’t compete with the seal-snatching airtime of the great white shark.
However, another reason reef sharks receive less attention is that they are a rare sight. Coral reef biologist Alan Friedlander from the University of Hawaii told me that he can’t remember the last time he saw a shark in the Caribbean – and he’s studied those reefs for 25 years.
Are there so few reef sharks because of human activities such as fishing and finning, or were there never very many to start with? To answer this question, a team of marine biologists (which did not include Friedlander) decided to count reef sharks at coral reefs close and far to human settlements to better understand how humans impact their populations.
The results are staggering: the scientists estimated that, throughout the Pacific islands they studied, reef shark density is only 3-10% what it would be if no humans lived in the area. And just 100 people living within 200 kilometers of the coast was enough to drive most of the sharks away from the reefs.
Of course, people aren’t just going to up and leave their homes so the reef sharks can reclaim theirs. But the researchers are working to understand why exactly the sharks disappeared to help conserve them and their habitat.
Although there are no active reef shark fisheries in the US Pacific, the reef sharks' disappearance could be caused by recreational fishing or illegal shark finning, which, combined, kill 26 million to 73 million sharks each year. Another possible explanation is that the reef sharks are starving. Their food sources, including coral reef fishes, are decreasing in number because of habitat destruction and human exploitation, and could be taking the sharks with them.
But another potential cause is that these sharks are skittish around people. So when too many people move into the area, the reef sharks flee to other coral reefs. Indeed, the researchers found far more sharks at small, isolated reefs than they expected. But this in itself is a danger to the reef sharks. With so many sharks concentrated in a small area, “if you really wanted to, you could fish out a few hundred sharks very easily,” said Friedlander.
This study, published today in Conservation Biology, is a good reminder that, while sharks have a bad reputation for being bloodthirsty, we do more harm to them than they do to us. For more information, read “5 Reasons to Revere, Not Fear, the Shark.”