Canadians in their prime working years were less likely to hold full-time, year-round jobs in 2015 than at any time in the past two decades, new census data show, with declines particularly pronounced among men.

The shift to part-time and part-year work carried implications for everything from household finances to retirement savings, consumer spending and tax returns.

The share of those 25 to 54 in full-year, full-time work tumbled to 49.8 per cent in 2015, according to the latest tranche of census data. The slide occurred among both men and women, but was most acute among those core-aged men, where the proportion in these jobs sank to the lowest level since comparable record-keeping began in 1980.

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The census release highlights broad, seismic changes in the composition of Canada's labour market: A growing share of seniors are working and immigrants comprise a greater portion of the work force, while employment among youth – particularly young men – has declined. At the same time, the most common jobs in Canada – such as retail salespersons and truckers – are also among those most at risk for automation.

The decline among full-time core-aged workers "is concerning – these should be your prime working years," said Pedro Antunes, deputy chief economist at the Conference Board of Canada. Although the economy has added full-time positions more recently, in the long run, "the fact that we're not fully employed, or not as employed as we'd like to be, does mean weaker income and weaker potential for those households and for the economy at large."

The share of working-age men in full-time, year-round jobs fell to a record low of 56.2 per cent, from 63.3 per cent a decade earlier. The proportion of women in this group fell to 43.7 per cent, the lowest since 2000, from 46.4 per cent. (The participation rate for this age group has held at 86 per cent or 87 per cent in the past decade, separate labour force survey data show).

In Calgary, where the economy is improving but job growth remains weak, Mohan Acharya works two part-time jobs to make ends meet.

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Trained as an engineer in his native Nepal, Mr. Acharya immigrated to Canada 10 years ago – and picked Calgary as his new home based on what was then the city's hot economy. He got his millwright certificate and found a string of full-time jobs with several employers.

But three years ago, as oil prices plummeted, he was laid off and took a part-time job as a security guard. Some months, he gets full-time hours, some months, he does not. His $18-an-hour salary, along with his wife's part-time job at Costco, allows the family to cover rent and other expenses.

"This is my survival job. If I didn't do this job, it would be difficult to survive," the 55-year-old said.

Statistics Canada said the decline in full-time work among the 25-to-54 age group stems from multiple factors, such as growth in services jobs, the 2008-09 recession, more automation and a shift to more flexible work schedules. "There's a series of factors that are all coming together that are pushing these levels down over the past 10 years. But we can't pinpoint and we can't quantify exactly how much each of these factor is contributing," said Vincent Dale, assistant director at Statscan's labour-statistics division.

The employment drop in this age group is not confined to just one province or one sector – it's generally "across the board," Mr. Dale said. The decline was particularly steep among people with lower levels of education, and among those in Alberta, he noted. And although structural shifts in the economy are playing a role, he said, in some cases, people may be opting to work reduced hours or only for certain parts of the year.

Young people were less likely to work in 2016 than a decade earlier, especially young men. And employment fell for both those who attended school and among those who didn't.

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"We've not done the best job in terms of engaging younger people in the labour market," said Mr. Antunes of the Conference Board, by, for example, better directing youth to where the job opportunities are, ensuring they have relevant skills, or creating opportunities for work experience.

Meantime, the share of seniors in the workplace has surged. Almost one in five Canadians aged 65 and older worked at some point during 2015 – nearly double the proportion a decade earlier.

By composition, the services sector accounts for a growing share of employment in the country, where nearly four in five Canadians now work. Health care and social assistance is the biggest sector by employment, followed by retail trade.

Among women, the most common jobs were retail salespersons, registered nurses and cashiers. Among men, the most common occupations were transport truck drivers, retail salespersons and retail managers.

The census also showed diverging labour-market outcomes among Indigenous people. The employment rate for those living on reserves was 37.9 per cent – with a 22.5-per-cent jobless rate, while the employment rate among those living off reserve was 60.4 per cent, with a 7.6-per-cent unemployment rate. Most employment rates for core-aged Indigenous groups declined from 2006 to 2016, the agency said – despite rising levels of educational attainment.

The census comes as Canadians experienced profound economic changes in the 10-year period, with the 2008 recession followed by a recovery and surging house prices, especially in Vancouver and Toronto. The census is based partly on 2015 trends, so it doesn't fully reflect the impact of the oil-price drop that hurt resource-related provinces such as Alberta and Newfoundland, nor full-time job growth in some provinces since then.

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Back in Calgary, Mr. Acharya took an extra part-time job a year ago, delivering food and helping in the kitchen at Mount Everest, a Nepalese restaurant, to try to build some savings. He still hopes his wife will some day be able to find higher-paying work, allowing him the time to become accredited as an engineer .