Sharks have been present on the planet for more than 400 million years and are represented by hundreds of different species. Despite their long standing presence on the planet, sharks are now considered by many to be at risk of extinction, especially particular species. Declining shark populations are largely attributed to shark finning and fishing in general. The IUCN indicates that approximately a third of all shark species are currently threatened with extinction.
The United Nation’s Food and Agriculture Organization estimates that at least half of the world’s sharks are overexploited and in danger of extinction. Sharks have low fertility rates combined with long lives that do not enable them to bounce back as quickly as some species might. Now a new study is shedding light on the impact of human populations on reef sharks, sharks which are important to already suffering reef systems globally.
The new study published in the journal Conservation Biology focused on the impact of human populations on reef shark populations in the Pacific Ocean. The study, led by Marc Nadon from the University of Miami, focused on the central-western portion of the Pacific, which included uninhabited islands, American Samoa and Hawaii. Sharks of the reef shark grouping were the focus, including the tawny nurse shark, gray reef shark and whitetip reef shark.
The study used shark survey dives conducted by the National Oceanic and Atmospheric Administration, which amounted to over 1,600 dives in forty-six different reefs. The researchers used the information obtained on these dives and analyzed it for nearby human populations, ocean temperatures and food availability, amongst other concerns. By comparing the recorded findings of dives to these elements, the researchers determined that the human population was the greatest influencer on the shark populations.
Nadon stated: “Around each of the heavily populated areas we surveyed- in the main Hawaiian Islands, the Mariana Archipelago and the American Samoa- reef shark numbers were greatly depressed compared to reefs in the same regions that were simply away from humans. We estimate that less than ten percent of the baseline numbers remain in these areas.”
The reasons for the greatly reduced populations of reef sharks, estimated at more than ninety percent lost, are thought to be fishing, both legal and illegal, and reduced food availability due to diminishing fish from further fishing by the nearby human populations. These factors were found to be more devastating to the populations than global warming impacts, according to the study.