Humans are causing a steep decline in populations of reef sharks in the Pacific Ocean according to a new study by a group of international marine scientists . The new estimates of reef sharks compared numbers around populated islands with those living near uninhabited ones . The results were sobering , say researchers . `` We estimate that reef shark numbers have dropped substantially around populated islands , generally by more than 90 % compared to those at the most untouched reefs , '' said lead author Marc Nadon from the Joint Institute for Marine and Atmospheric Research at the University of Hawaii . Over 1600 underwater surveys across 46 U.S. Pacific islands and atolls were undertaken in the study and combined with data on human population , habitat complexity , reef size and satellite records . The estimates were gathered using `` towed-dive surveys '' where paired SCUBA divers record shark sightings while being towed behind a small boat . It 's a method which provides a more accurate census of mobile reef fish like sharks over large areas , according to researchers . `` 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 further away from humans , '' Nadon said . `` We estimate that less than 10 % of the baseline numbers remain in these areas , '' he added . Co-author of the study , Julia Baum from Canada 's University of Victoria says the human disturbances to reef shark populations are likely down to fishing -- either incidentally caught in the nets of commercial or recreational fishermen or by direct targeting for their fins . `` Reef shark fins are not the most valuable because they tend to be smaller than other sharks , but a lot of other oceanic sharks have already declined a lot so that 's why fisherman are now turning to them , '' Baum said . She estimates these fins sell for around $ 100 per kilogram with demand coming from Asian markets where shark fin soup can be found on the menu for weddings and business banquets . Reef sharks , which are around six to eight feet long ( 1.8 meters to 2.4 meters ) , are the `` apex predators '' of coral reefs Baum says , and like predators in other eco-systems play an important role in structuring food webs . But there is still much to learn about their specific role . `` Frankly , we 're still trying to figure out what predators do on reefs . The reason for that is because most predators have been removed from reefs . Most reefs that coral reef biologists study are moderately to heavily degraded , '' Baum said . The study forms part of the U.S. 's National Oceanic and Atmospheric Administration 's Pacific Reef Assessment and Monitoring Program and is published online in the journal Conservation Biology .
New study provides estimates on reef shark populations near islands in Pacific Ocean . Marine scientists find reef shark numbers dramatically reduced around inhabited islands . Over 1600 surveys make up study which forms part of NOAA Pacific monitoring program .