12/27/2013 10:50 EST | Updated 02/26/2014 05:59 EST

BlackBerry shares down 8% on TSX

Days after an unexpected jump higher, shares in BlackBerry wiped out most of their recent gains and traded down by almost 10 per cent on Canada's benchmark stock exchange Friday.

BlackBerry shares were off by almost 80 cents to $7.56 shortly after trading opened in Toronto. The shares were playing catch-up to what happened in New York yesterday, when the TSX was closed for Boxing Day but the Nasdaq was still open.

The company, whose stock trades on both exchanges, was hit by news that co-founder Mike Lazaridis is selling $26 million worth of his remaining stake, in effect exiting the company completely.

Lazaridis has sold 3.5 million of his BlackBerry shares since Monday, bringing his total ownership below the five per cent threshold that requires him to report his holdings to regulators.

Last week, the company posted disastrous quarterly earnings that showed a $4-billion writedown related to unsold inventory. But despite the bleak number, the company's shares gained 16 per cent last Friday.

Speculation at the time was that part of the reason for the sudden bounce was short-sellers giving up their positions, a counter-intuitive phenomenon whereby the stock sees a sudden but temporary surge in buyers because everyone who had been betting against the company gives up.

Trading activity today appears to back that up, as BlackBerry shares have headed lower again.

BlackBerry practically invented the smartphone industry and remained among the prominent players in the handset arena until fairly recently. But it has lost a major chunk of its market share to rival companies such as Apple, Samsung, LG, HTC and others.