Prime Minister Stephen Harper's Conservatives are losing incumbents leading up to next year's election, with more MPs bowing out than before the 2011 vote.

In the past week, Tory backbenchers Brian Storseth and Rick Norlock announced they would not seek re-election. With their departures, at least 18 of the 162 current Conservative MPs have said they will not run again next year. Another seven Tory MPs have already resigned mid-term and triggered by-elections, with another by-election coming up after the passing of Jim Flaherty.

The departure figures dwarf those from the period leading up to the 2011 election, back when the Conservatives held a minority. Only seven then-incumbent Conservative MPs declined to run again in 2011, and only two resigned, triggering by-elections.

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The latest moves leave Mr. Harper's Conservatives losing familiar faces as they trail Justin Trudeau's Liberals in polls. Incumbents often have an advantage in an election, though many of the departing Conservatives hold seats that are considered safe for the Tories.

Mr. Norlock, 66, is retiring to spend more time with family and said he doesn't think polls have affected any decision of his fellow departing Conservatives.

"I'm being frank – I don't know of anybody who said, 'I'm going to leave because I think I'm going to lose my seat,'" Mr. Norlock, who represents the Ontario riding of Northumberland-Quinte West, said Friday. Current polls, he added, are too early to provide a firm picture of 2015.

He first won his seat in 2006 after three decades as a police officer, and said his job left him too little time to visit his grandchildren. He told Mr. Harper of his departure earlier this year. "He basically said, 'If I was your age, he said I'd probably be thinking the same way,'" Mr. Norlock said.

He was surprised by the pace of government. "It used to frustrate me how slow provincial governments worked," he said. "And what frustrates me federally is that … it's even slower."

New Brunswick MP Mike Allen, first elected in 2006, is also among the Conservative MPs who will not seek another term. He announced his decision five months ago, and said Mr. Harper was also supportive of him. Mr. Allen, 53, hopes to re-enter the private sector and decided to bow out now, joking he wanted to leave before his "best before" date and while still healthy.

"When you come to the conclusion that maybe you're more fearful of winning than losing, and putting yourself on a track for another four years – because I would never quit partway through a term – I just felt in my own heart of hearts that I didn't think I could give it the same oomph that I had," he said Friday. The other departures did not factor into his own, he said. "Everybody's got to make their own decision," Mr. Allen said.

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Mr. Storseth, 36, announced his resignation Thursday. He'd represented his rural Alberta riding since 2006, and has young twins. "My children and my wife are the light of my life and being almost 4,000 kilometres away from them most of the year has been incredibly difficult," he said.

Mr. Storseth has been speaking out against his own government's changes to rein in the Temporary Foreign Worker program, which he sees as an essential labour stream in some labour-starved parts of Alberta. It was a rare break in caucus unity, but Mr. Storseth said the issue did not play a role in his decision. "This was based 100 per cent on family and a desire to be back in Alberta," he said.

Other Tory MPs who have announced they won't seek re-election include British Columbia's Russ Hiebert, James Lunney and Colin Mayes; Alberta's Diane Ablonczy, Laurie Hawn and LaVar Payne; Saskatchewan's Ray Boughen, Garry Breitkreuz, Ed Komarnicki and Maurice Vellacott; Ontario's Barry Devolin and Gordon O'Connor; and Nova Scotia's Gerald Keddy and Greg Kerr.