BOSTON ( TheStreet) -- Let's take a look at selected trading in biotech and drug stocks in the third quarter now that hedge funds and other institutional investors filed 13Fs Wednesday night. Amarin ( AMRN) is a good place to start, given recent volatility in the stock due to the uncertainty over Vascepa's New Chemical Entity (NCE) status and the prescription fish oil pill's commercial launch. Vascepa was approved in July, so during the third quarter. Deerfield Management is the most noteworthy new hedge fund to buy into Amarin, taking a 2.7 million-share position in the third quarter. Other new Amarin buyers in the third quarter were Miura Global Management (1.5 million shares) and Vertex One Asset Management (1 million shares), according to Whale Wisdom, which tracks 13F filings. Amarin also saw significant selling in the third quarter, led by Brookside Capital Management exiting the stock entirely with the sale of 4.8 million shares. Billionaire hedge fund manager Steven Cohen of SAC Capital sold 4.7 million Amarin shares although he retained a 1 million-share position as of the end of the third quarter. Additional big Amarin sellers included Sectoral Asset Management (2.7 million shares), AllianceBernstein (2.4 million shares), Lord, Abbett & Co. (2.2 million shares) and Abingworth (2 million shares), according to Whale Wisdom. A note of caution about interpreting 13F filings: Hedge funds and mutual funds that manage more than $100 million are required to disclose their equity holdings, options and convertible debt on a Form 13F filed SEC within 45 days of the end of a quarter. Funds aren't required to report short positions betting on declines, nor do they disclose the timing of their purchases or sales. Since we're already midway through the fourth quarter, the positions in biotech and drug stocks reported on these latest 13Fs may already have changed. Sarepta Therapeutics ( SRPT) shares jumped from $15 to $44 on Oct. 3, after the reporting period covered by this latest crop of 13Fs. Sarepta also disclosed that it raised close to $40 million via stock sales during a six week period that brackets the end of the third quarter and the beginning of the fourth quarter.
With those caveats in mind, Perceptive Advisors was the largest buyer of Sarepta in the third quarter, adding 1.4 million shares. Wellington Management also bought 1 million shares. BlackRock was a notable (perhaps regretful) Sarepta seller, shedding 8.5 million shares across two different entities, according to Whale Wisdom. For Arena Pharmaceuticals ( ARNA), three new buyers of note during the third quarter, which began right before the approval of the company's weight-loss pill Belviq: Deerfield Management (7.8 million shares), Capital World Investors (5 million shares) and QVT Financial (2.7 million shares) Blackrock sold 9.9 million Arena shares during the third quarter. There was also significant net-selling options activity in Arena from Susequehanna International, Barclays, Group One Trading and Citigroup, according to Whale Wisdom. Spectrum Pharmaceuticals ( SPPI) lost Tang Capital as a major shareholder in the third quarter. The San Diego-based hedge fund sold 4 million Spectrum shares, retaining 1.5 million shares. -- Reported by Adam Feuerstein in Boston. Follow @AdamFeuerstein