PEW Global Shark Assessment
PI: the late Dr. Ransom Myers, Dalhousie University*
The Pew Global Shark Assessment led by the late Dr. Ransom Myers of Dalhousie University in Nova Scotia produced an unprecedented body of knowledge about the alarming disappearance of sharks in oceans around the world, and has drawn important connections between the loss of these marine predators and a continuing breakdown of ocean ecosystems. By providing a clearer understanding of what we have lost, this work has made it possible to develop management and restoration goals for these shark species.
Supported with a grant from the Institute for Ocean Conservation Science (formerly the Pew Institute for Ocean Science), the Pew Global Shark Assessment resulted in 31 peer-reviewed publications, including two significant papers in Science that received extensive media coverage. This project has educated the public and policymakers regarding the urgent need to better protect large sharks and the dire consequences to ecosystems if we do not. In protecting these large, charismatic, but very vulnerable species, shark conservation also offers the opportunity to save the myriad other species and ecosystems with which sharks interact.
The Assessment was begun in 2003 by Dr. Myers, a world-renowned fisheries biologist, and completed by his laboratory team after his untimely 2007 death. One of the most significant products of this work was a March 30, 2007 paper in Science directly connecting the dramatic overfishing of our largest sharks, to the decline of shellfish on the U.S. Atlantic Coast. The team found that overfishing of large sharks such as the bull, great white, dusky, and hammerhead has resulted in a population explosion of the “prey” animals they eat. Abundant like never before, these “prey” species – rays, skates, and smaller sharks -- are gorging freely on shellfish at unprecedented rates. The decimation of the largest shark species has been astonishing: tiger sharks and scalloped hammerhead sharks declined by more than 97 percent between 1970 and 2005, researchers determined, while bull, dusky, and smooth hammerhead sharks may have declined by more than 99 percent in that period.
This research also uncovered the drastic decline of oceanic sharks in the Gulf of Mexico due to exploitative commercial fishing operations, which have placed certain species at risk of being permanently eliminated. A February 2004 paper by Dr. Myers and researcher Dr. Julia Baum in Ecology Letters determined that oceanic whitetip shark populations have plummeted by 99 percent in the Gulf from the mid-1950s to today, and continue to disappear. Two other commonly caught shark species, silky and dusky sharks, have declined by approximately 91 and 79 percent, respectively, the team found. These sobering numbers prove the staggering impact of modern fishing fleets on sharks and the need for decisive policy intervention.
The Pew Global Shark Assessment further provided new and insightful information about the shrinking abundance of open-ocean fish in the tropical Pacific and the far-reaching consequences of this disturbing trend. Populations of blue, mako, oceanic whitetip, silky, and thresher sharks, as well as tuna, have declined dramatically in both abundance and biomass since the 1950s, when commercial fishing operations first deployed longlines in the Pacific Ocean, Dr. Myers and Dr. Peter Ward reported in a 2005 paper in Ecology. Longlines are fishing lines that may extend for 50 miles and have 1,200 dangling baited hooks. These hooks catch and kill not only targeted species but also animals not being sought, known as bycatch. Death-by-bycatch is the dominant threat to open-ocean sharks. Not only do the snared animals die, but they are commonly caught at or below the size at which they reproduce, the research team showed. The result is that fewer and fewer juvenile sharks are being left in the ocean to reach sexual maturity and help replenish the population. In the most alarming example, silky sharks caught on longlines now average 97 cm in length, less than half the size at which they mature, researchers found. In addition, the drastic loss of top predators is upsetting the balance of the entire ocean, leading to a greater abundance of small species such as the pelagic stingray.
Many of the next-steps in this important work are being pursued by the Lenfest Ocean Program of the Pew Charitable Trusts. The Lenfest program is continuing to identify global patterns of diversity and extinction risk in sharks, rays and chimaeras (deep-sea fish related to sharks), including an assessment of sharks’ status in the Mediterranean and an evaluation of their status in reef communities using sighting data from recreational divers.
More Information: Ram Myers' Legacy Website | Lenfest Ocean Program
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