(Adds details on specific stocks, updates prices)
* TSX down 107.76 points, or 0.69 percent, to 15,437.06
* All of the TSX's 10 main groups fall; energy group down 2.3 pct
TORONTO, March 14 (Reuters) - Canada's main stock index lost ground on Tuesday as falling oil prices weighed on the country's substantial oil and gas sector and Valeant Pharmaceuticals International Inc stock plunged on the exit of an activist investor.
The energy group retreated 2.3 percent as oil prices fell to three-month lows after OPEC reported that crude inventories in developed countries had risen above the five-year average in January despite production cuts by some of the world's largest exporters.
The most influential movers on the index included some of its biggest energy companies with Suncor Energy down 1.7 percent at C$39.78 and Canadian Natural Resources losing 2 percent to C$41.84.
Valeant slumped 9.3 percent to C$14.70 after billionaire investor William Ackman walked away from the struggling drug company after trying to rescue it for some 18 months, taking a loss of more than $3 billion.
At 10 a.m. EDT (1400 GMT), the Toronto Stock Exchange's S&P/TSX composite index fell 107.76 points, or 0.69 percent, to 15,437.06.
All of the index's 10 main groups were in negative territory, with four decliners for every advancing stock.
Convenience store operator Alimentation Couche Tard Inc fell 4.5 percent to C$59.02 after reporting earnings that missed analyst estimates.
The materials group, which includes precious and base metals miners and fertilizer companies, lost 0.8 percent while industrials fell 0.5 percent.
Gold prices were steady, while copper prices declined 0.9 percent to $5,743 a tonne.
U.S. crude prices were down 2.3 percent to $47.3 a barrel, while Brent lost 1.9 percent to $50.36.
Canadian home prices rose in February as prices continued to climb in the hot Toronto market, data showed on Tuesday in a report that was unlikely to alleviate concerns from some quarters that the city is facing a real estate bubble. (Reporting by Alastair Sharp; Editing by Bill Trott)