Jonathon Jacobson, Eton Park Short Shire plc, Bet Against Paulson

Shire hasn't had the best quarter as shares of the pharmaceutical company slumped by nearly 18% in the first three months of this year. According to disclosures filed with the U.K.'s Financial Conduct Authority, hedge funds started shorting Shire at the beginning of this year. The most notable of these short-sellers are Jonathon Jacobson's Highfields Capital Management and Eton Park International. The latter reduced its short from nearly 1% of Shire's outstanding shares to 0.58% on April 6. Highfields currently holds a short in 0.7% of Shire's shares. Other short-sellers include Oz Management and Taconic Capital Advisors.

These bears are betting against billionaire John Paulson. At the end of 2015, John Paulson & Co. held 6.8 million shares of the U.K.-based pharmaceutical company, which amounted...