One out of every four inmates who cycled through federal penitentiaries last year spent some time in solitary confinement, an extreme form of incarceration that is undermining efforts to rehabilitate offenders, Canada's prison watchdog says.

Segregating a man or woman from the rest of the population is supposed to be used sparingly as a last resort, Howard Sapers, the Ombudsman for federal prisoners, said in an interview on Sunday. But the agency that runs Canada's 47 federal prisons and community corrections centres is increasingly turning to solitary confinement to manage institutions that are crowded and lack sufficient resources to deal with high-needs inmates, Mr. Sapers said.

"It's become a default population-management strategy," he said.

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A special report published in The Globe and Mail on Saturday chronicled the life and death of one of these inmates: Edward Christopher Snowshoe, of Fort McPherson, NWT, who suffered from mental-health issues. During his three years in a maximum-security prison in Edmonton, Mr. Snowshoe tried suicide four times. He was 24 when he hanged himself in a two-by-three-metre isolation cell on Aug. 13, 2010. He had spent 162 consecutive days in solitary confinement.

Mr. Snowshoe has become another sad statistic: The suicide rate in federal prisons is seven times that in the public at large, with nearly half taking place in segregation.

The federal government has displayed little interest in curbing the use of solitary confinement.

Public Safety Minister Steven Blaney was not available for comment on Sunday but Jason Tamming, a spokesman for the minister, said in an e-mailed response that the Conservative government's tough-on-crime agenda amounts to "strong action" that is keeping streets and communities safe.

"Our efforts will continue to be focused on the victims of crime," Mr. Tamming said.

Amid mounting evidence on the dangers of solitary, the number of federal inmates in segregation is growing in Canada, leaving it out of step with the United States and other countries that are weaning prisons off the practice.

Of the 21,100 men and women who flowed through the federal prison system in the fiscal year ended March 31, 2014 – a figure that includes those already behind bars, new admissions and those released on parole – nearly 5,100 of them spent time in isolation, according to figures provided to The Globe by Mr. Sapers.

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Correctional Service Canada's overreliance on solitary confinement is at odds with the reasons why society incarcerates those convicted of crimes in the first place: to rehabilitate and prepare them for eventual release back into the community, said Mr. Sapers, who has long urged the agency to introduce a ban on placing inmates with mental-health or suicide issues in segregation.

"The purpose of corrections in Canada is not to isolate and dehumanize people," he said.

The problems associated with isolation are not new.

One year ago, a coroner's inquest into the death of Ashley Smith, a New Brunswick teen who took her life while in Correctional Service custody in 2007, recommended strict limits on solitary confinement: a maximum consecutive stay of 15 days, and a cap of 60 days during a calendar year.

In 1996, an Ontario Court of Appeal judge endorsed a similar, 60-day cap.

But there is no cap on time spent in solitary in a federal prison.

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Roughly one-third of federal inmates in solitary confinement in fiscal 2014 languished in an isolation cell for more than 60 days, according to Mr. Sapers' Office of the Correctional Investigator.

The federal government has not yet responded to the coroner's inquest into Ms. Smith.

Mr. Sapers said federal officials have told him to expect a response before the end of the year.