What: Shares of GoPro (NASDAQ:GPRO) fell as much as 16% early Thursday, then partially recovered to trade down 9% as of 11:45 a.m. after the action camera specialist released disappointing fourth-quarter results and a light forward outlook.

So what: Quarterly revenue fell 31.1% year over year to $436.6 million, which, incidentally, came in slightly above GoPro's recently reduced guidance last month, when it called for a 31.4% decline to $435 million. This includes a $21 million reduction resulting from price protection charges after GoPro reduced the price of its HERO4 Session camera by $100 to $199.

Meanwhile, adjusted earnings before interest, taxes, depreciation and amortization (EBITDA) swung to a loss of $9.3 million. On the bottom line, GoPro incurred a GAAP net loss of $34.5 million, or $0.25 per share, and an adjusted net loss (excluding stock-based compensation and acquisition expenses) of $11.4 million, or $0.08 per diluted share.

That said, GoPro's adjusted gross margin for the quarter was 29.6%, a decrease from 48% in last year's fourth quarter, and below GoPro's guidance for 34.5% to 35.5%. In particular, this was caused by a $57 million charge to cost of revenue for excess purchase order commitments, excess inventory, and obsolete tooling, greater than the $30 million to $35 million GoPro told investors to expect when it reduced guidance last month. According to GoPro, the difference was due to its subsequent "decision to discontinue production of the HERO cameras," which effectively simplifies GoPro's product offerings going forward to just its higher-end -- and higher-margin -- HERO4 Black, HERO4 Silver, and HERO4 Session cameras.

GoPro CEO Nick Woodman elaborated:

In 2015, we recorded 16% year-over-year revenue growth and the fourth quarter represented the second highest revenue quarter in the company's history. However, growth slowed in the second half of the year and we recognize the need to develop software solutions that make it easier for our customers to offload, access and edit their GoPro content.

Now what: Things weren't much prettier looking forward. For the current quarter, GoPro anticipates revenue of $160 million to $180 million (down over 53% from the same year-ago period), adjusted gross margin of 36%, and an adjusted EBITDA loss of $95 million, plus or minus $2.5 million. For full-year 2016, GoPro expects revenue of $1.35 billion to $1.5 billion, down 16% to 17.4% from the $1.62 billion in revenue it achieved in 2016.

As I suggested in my full earnings take last night, that doesn't preclude the possibility that GoPro is purposefully offering conservative guidance ahead of the launch of its new Karma drone, and a widely expected refresh of its camera lineup later this year. But as it stands, given its relative underperformance and disappointing outlook, it's no surprise GoPro stock is now trading at its lowest level since the company's IPO in mid-2014.

Steve Symington has no position in any stocks mentioned. The Motley Fool owns shares of and recommends GoPro. 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.