HALIFAX -- A new study says while Atlantic Canada's largest city is growing, population rates in Halifax remain marginal because more people are moving elsewhere.

The Greater Halifax Partnership said Thursday that the city's population grew by four tenths of one per cent in 2013, a rate slower than most Canadian cities and half the normal rate of growth.

"If our population declines, our fiscal sustainability is threatened," the report states. "We've seen this happen first-hand in communities across the province. In addition, weak population numbers threaten most outcomes across the range of indicators."

Chief economist Fred Morley says keeping population growth rates high through retaining immigrants and new university graduates is key to supporting business and to growing the tax base.

The study says since 2001, migration has accounted for two thirds of Halifax's population growth. It also says immigration to Halifax hit an eight-year low last year and that the weak population growth in 2013 was due to declining immigration and a large spike in residents moving west to other provinces.

"The biggest challenge we face as a community is hanging on to our new graduates and attracting immigrants," it says.

Premier Stephen McNeil said his government is studying the immigration issue and will soon produce a strategy on how to attract people to the province and keep them here.

"I think Nova Scotians, regardless of where they live, will embrace an immigration strategy that actually will retain people in the province -- people who are investing in communities, people who are running businesses, providing economic opportunities and, quite frankly, giving opportunities for our sons and daughters to stay here," he said.

McNeil said the strategy has to appeal broadly to potential immigrants and native Nova Scotians who have moved away to seek better opportunities.

"It's also important to recognize that as the economy improves, as we create economic opportunity, we need to bring people back," he said. "There's a lot of our sons and daughters that don't live in this province...and we need now to ensure that the economy is moving forward to create the job opportunities for them."

The study, known as the Halifax Index, says key economic opportunities lie in such things as increasing density in the city's centre, retaining regional and head business offices and in making Halifax a major centre for big data research and business.

The index measures progress in Halifax against five benchmark cities including; Quebec City, London, Ont; Regina, Victoria and St. John's, N.L.