Murdoch and his colleagues' new, mathematical estimating method uses trade records from commercial markets and genetic techniques to identify species.
In their effort to accurately estimate the number of fins harvested—and therefore the number of sharks killed—the scientists conducted interviews with traders, studied thousands of auction records, observed auctions and shops for 18 months, and analyzed hundreds of fin samples.
In the end the researchers concluded that from 1996 to 2000 26 to 73 million sharks were traded yearly. The annual median for the period was 38 million—nearly four times the UN estimates but considerably lower than those of many conservationists.