New York City lost 39 percent of its apartments affordable to low-income families between 2002 and 2011, according to a new report.

There was a net loss of about 385,000 affordable apartments, says the Community Service Society of New York, a nonprofit organization that advocates for low-income residents.

The group says rising rents during the period led to the dramatic decline in the supply of apartments affordable for families with incomes at or below 200 percent of the federal poverty threshold. CSS’s study used the generally accepted standard that a household’s monthly housing costs should not exceed 30 percent of its monthly income.

Under Mayor Michael Bloomberg, the city produced 45,000 new income-targeted apartments and helped preserve more than 100,000 affordable housing.

“The Bloomberg administration did a lot but not enough to keep pace,” says Tom Waters, housing policy analyst for CSS.

The dwindling supply is attributed to landlords raising rents when an apartment turns over. For example, an apartment in the Bronx may have been $900 per month. However, when that unit’s family moves out, the rent may be increased to $1,250 for the next family, Waters says, noting that rents can go up even in rent-regulated units.

For a household earning $35,000, the new rent would be nearly 43 percent of it income.

The CSS report, What New Yorkers Want From the New Mayor: An Affordable Place to Live, offers several recommendations on how to increase and improve affordable housing.

The organization urges new Mayor Bill de Blasio to continue a large-scale affordable housing program along the lines of Bloomberg’s housing plan while prioritizing more housing for people with the lowest incomes.

Other recommendations include eliminating $100 million in New York City Housing Authority (NYCHA) payments to the city for policing service, payments in lieu of taxes, and other charges; halting NYCHA’s infill development process of leasing land to developers to build market-rate properties; and using mandatory inclusionary zoning to augment affordable housing development.

Donna Kimura is deputy editor of Affordable Housing Finance. Connect with her on Twitter @dkimura_AHF.