Apartment rents rose during the first quarter, ending five straight quarters of declines and signaling the worst may be over for the hard-hit sector. Nationally, the apartment vacancy rate stayed flat at 8%, the highest level since Reis Inc., a New York research firm, began its tally in 1980. Reis tracks vacancies and rents in the top 79 U.S. markets, and rents rose in 60 of them, led by Miami, Seattle and New York—all cities that have notched big rental declines in the past year. Rents increased 1.6% in the first quarter in Miami and 0.9% in New York. The gains came during what is usually a seasonally weak period for apartments and suggested that landlords may have some momentum heading into the peak spring and summer leasing season.