Every two weeks brings new readings on the short interest on every Nasdaq and New York Stock Exchange listed stock. Some companies see short interest in their shares rise, and other companies see their short interest  fall.

What catches the eye of 24/7 Wall St. is when the short interest drastically changes, or when there is an apparent targeting by short sellers. For the May 13, 2016, settlement date, the short interest surged or posted unusual gains in several notable companies.

We have added in trading data and color on each to avoid just making data without consideration of what the reasons or the implications may be. Here are eight well-known stocks with either unusual or massive gains seen in their short interest.

Abbott Laboratories (NYSE: ABT) saw its May 13 short interest jump a sharp 300% from the end of April. The new short interest was 40.29 million shares, up from 9.89 million shares. The number is massive on the surface, but it still is only about 3% of the float.

Annaly Capital Management Inc. (NYSE: NLY) saw its short interest rise handily, likely as investors begin to brace for more chances of rate hikes ahead. This is a high-dividend mortgage real estate investment trust (REIT) player (11% yield), so interest rates may matter to more than just a few of its investors. The new short interest is 41,310,727 shares, up 24% from the 33,321,964 shares short at the end of April.

Baxter International Inc. (NYSE: BAX) saw its May 13 short interest rise sharply to 120.6 million shares. This was from some 57.4 million shares short at the end of April. This rise was over 63 million shares in the short interest, a gain of about 110%. 24/7 Wall St. noticed that Baxter has now joined the list of the five most shorted NYSE stocks.

Delta Air Lines Inc. (NYSE: DAL) was the airline with the largest nominal gain in shares short. For the May 13 settlement date, it jumped to 27,998,610 shares from the 20,069,637 shares short at the end of April. That rise of almost 8 million shares is also a gain of some 39.5%. Is spending a lot on new security systems to move you through faster a bad thing? Maybe being last in customer service was the driver here.

Rite Aid Corp. (NYSE: RAD) saw its short interest rise to 45,773,095 shares as of the May 13 settlement date. This is a 7% gain from 42,762,822 shares short at the end of April. If a 7% increase in the short interest doesn’t sound like much, think about what it means. Can you say more trouble in the land of pending mergers?

Square Inc. (NYSE: SQ) saw such a large number of shares short that the notation is likely more pointed at the lock-up expiration rather than targeting Jack Dorsey (see Twitter below). The May 13 settlement date saw Square’s short interest rise to 19,158,374 million shares. The total at the end of April was 15,282,791 shares. That 25% pop in the short interest would have been almost 88% of the entire float, but again that is tied to a May 17 lockup expiration that was set to release millions of shares from insiders to be free to be sold.

Twitter Inc. (NYSE: TWTR) is no stranger to bad news, with two downgrades seen this week alone. Short sellers are deciding to pile harder against it here, with the May 13 short interest rising to a sharp 77,348,203 shares from 63,725,952 shares short at the end of April. This was just in time for shares to hit all-time lows.

Under Armour Inc. (NYSE: UA) has fallen out of favor for investors. Maybe its endless growth just couldn’t be sustained in manner to please hungry growth investors, and it has been called fully valued. The May 13 short interest was listed as 46,277,078 shares, up 21% from the 38,238,216 at the end of April. Now a whopping 25.5% of its float is counted in the short interest.

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