Various groups have been monitoring and calculating the extent of the decline in the shark population for some considerable time. This latest estimate fits with estimates from the mid-2000s, and follows what now seems to be an established trend.
And the main driver does indeed appear to be shark fin soup. A group monitored the total import of shark fins and shark fin products for a report in 2011, from which they said
"........mark important occasions such as weddings and business deals in China and some other Asian communities. An astonishing 10.3 million kilograms of shark fins and shark fin-based products were imported into Hong Kong in 2011, according to statistics released last week by the Pew Charitable Trusts Environmental Group in.... "
10.3 million kgs is an awful lot of sharks.
And interfering to such an extent in the food chain could have some potentially serious consequences;
http://www.livescience.com/7240-alarming-decline-sharks-causing-species-vanish.html