There were plenty of naysayers out there in an otherwise flat 2015, and they're getting louder as the year comes to a close. Short interest is starting to creep higher on some pretty popular stocks. Folks sell a stock short when they think it is heading lower. They sell it short, buying the position back when it's time to cover the wager.

Short interest comes and goes. Most growth stocks aren't necessarily experiencing a spike in traffic in bearish bets, but let's go over some of the stocks that were clocking in with 52-week highs on the number of shares sold short by either the end of November or the middle of December.

Company

Dec. 15

52-Week Low

Ambarella (NASDAQ:AMBA)

13.5 million

7.2 million

Baidu (NASDAQ:BIDU)

9.4 million

1.9 million

Shake Shack (NYSE:SHAK)

3.6 million

0.7 million

Netflix (NASDAQ:NFLX)

50.7 million

27.7 million

Keurig Green Mountain (NASDAQ:GMCR)

11.5 million

4.8 million

Data source: Nasdaq.com.

Feeding the bears
We can start with Ambarella. The maker of video chips used in wearable cameras, surveillance gear, and dashboard cams became a market darling when GoPro (NASDAQ:GPRO) hit the ground running as a hot 2014 IPO. Ambarella is the lone provider of the video chips in GoPro's wearable cameras. It's been a different story these days as GoPro's growth has run cold. Both stocks have taken a step back in 2015, but Ambarella's prospects are rosier. It's growing briskly in its other product lines, as security equipment and car cameras grow in popularity. 

Baidu is China's leading search engine, but it's hungry for more. It's investing in new initiatives that bridge online access with offline services. From travel bookings to meal delivery, Baidu's investing in initiatives that are squeezing margin and profitability in the near term. Its stock is closing lower in 2015, something that it has only done two other times since going public a decade ago. Bears don't seem to think that these bets will pay off, but Baidu's top-line growth remains impressive.

Shake Shack went public in January, and the "better burger" darling has had a wild freshman year. The stock more than quadrupled within its first four months of trading, only to give more than half of those gains back. That's the kind of wild trading that smokes out speculators. Shack Shack is expanding at a healthy clip, but the stock's lofty valuation saw the number of shares sold short spike north of 4 million by the end of November before dipping slightly earlier this month.

Netflix is the S&P 500's biggest gainer of 2015, and that's the kind of success that brings both bulls and bears to play. International expansion has held profitability back, but it's hard to bet against a streaming television leader that will top 75 million subscribers in a few weeks. Netflix has had a big run in recent years. It was the top S&P 500 performer in 2013, too. 

Finally, we have Keurig Green Mountain providing a cautionary tale for bears who like to pile on when a company seems to be on the ropes. There were a whopping 19.6 million shares sold short by the end of November, four times the short interest for Keurig Green Mountain in mid-February. We know how things played out this month. The company that pioneered single-serve brewing in K-Cups agreed to be acquired at a 78% premium. That smoked out the bears, with nearly half of them clearing out of their positions by mid-December. 

Don't lose your head
Investors on the long side of these five stocks don't need to panic. Ambarella doesn't have all of its eggs in the GoPro HERO basket. Baidu is still the top dog in the lucrative search market within the world's most populous nation. Shake Shack's comps continue to trounce industry averages. Netflix is nearing the end of its international expansion, and fat profitability will follow. Keurig Green Mountain is comfortably on its path to be taken out at $92 a share in cash in the next couple of months. 

Climbing the proverbial wall won't always pay off for the bears, especially if the companies do continue to improve on their fundamentals. The shorts are stacking up against all five stocks as 2015 comes to a close, but 2016 can be a year that the naysayers will regret.

Rick Munarriz owns shares of Ambarella, Keurig Green Mountain, and Netflix. The Motley Fool owns shares of and recommends Ambarella, Baidu, GoPro, and Netflix. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.