Once again we see the effects of humans on the natural environment.
Overzealous fishers have had a dramatic effect on populations of Pacific reef sharks in recent decades, causing their numbers to decrease by more than 90 percent, according to a new study by a team of American and Canadian researchers.
Drawing on new research that overlaps shark population data with information on human fishing activity in the Pacific, the analysis, published online Friday in the journal Conservation Biology, shows that shark populations fare worse the closer they are to people, even if the nearest population is an atoll with fewer than 100 residents.
Rapid Decline In Shark Population Near Populated Places
Near populated places, such as the main Hawaiian Islands and American Samoa, the study found, there were roughly 26 sharks per square mile. Remote reefs, such as in the Northwestern Hawaiian Islands and Johnson Atoll, a U.S. territory west of Hawaii, by contrast, boasted 337 sharks per square mile.
As reported by The Washington Post, the team of eight scientists examined the results of a decade of underwater surveys across 46 Pacific islands and atolls and found densities of reef sharks — gray, whitetip and blacktip reef sharks, as well as Galapagos and tawny nurse sharks — “increased substantially as human population decreased” and the productivity and temperature of the ocean increased.
“Our results suggest humans now exert a stronger influence on the abundance of reef sharks than either habitat quality or oceanographic factors,” the authors wrote.
“In short, people and sharks don’t mix,” Marc Nadon, the study’s lead author and a scientist at the University of Hawaii’s Joint Institute for Marine and Atmospheric Research, said in a statement.
The scientists relied on more than 1,600 “towed-diver surveys” for their study. This form of underwater survey, aimed at reaching a more accurate count of fast-moving, wide-ranging fish, entails having a pair of scuba divers record the number of sharks they see while being towed behind a boat.
The study showed both the potential conservation benefits, and limits, of creating marine reserves in remote areas. Several of the areas the researchers surveyed — including the northwestern Hawaiian Islands, three Mariana Islands and all of the islands in a region known as the Pacific Remote Island Area — enjoy a significant level of federal protection. Enforcement, however, is often absent.
How Is This Happening?
According to the study, the devastation of sharks in areas near human civilization could be the result of illegal fishing, incidental killing or fishing for sport. Human impact on the reef fish that sharks call dinner could also play a role. Human influences were shown to outweigh natural influences, such as warmer water temperatures, the researchers found.
“Our findings underscore the importance of long-term monitoring across gradients of human impacts, biogeographic, and oceanic conditions, for understanding how humans are altering our oceans,” said Rusty Brainard, head of the coral reef ecosystem division at NOAA’s Pacific Islands Fisheries Science Center, which conducted the shark surveys.
It seems that once again, humans are to blame for the rapid decline of a species, and yet sharks and other predators are essential for the ocean’s health. When will we learn?
Photo Credit: [bendersama]