NEW YORK (AP) - Barnes & Noble plans to continue to shrink its store base. The head of Barnes & Noble's retail group, Mitchel Klipper, said in an interview published Monday in The Wall Street Journal that the company will have 450 to 500 stores in a decade. That's down from about 689 currently. Klipper said the chain plans to close about 20 stores a year over the period. The largest traditional U.S. bookstore has been facing tough competition from online retailers and discounters that sell books and has been focusing on its Nook tablet, e-book reader and e-book business for growth. A spokeswoman for Barnes & Noble said Klipper's remarks don't mark any change in its store closing plan. "We have historically closed approximately 15 stores per year for the past 10 years," said spokeswoman Mary Ellen Keating. Some closings are due to the fact that stores are unprofitable and others are stores moving to better locations. Although Barnes & Noble has for the most part stopped opening new stores in the past several years, Keating said New York-based Barnes & Noble opened two new prototype stores in 2012 and plans to test other prototypes in 2013. "The company's management is fully committed to the retail concept for the long term," Keating said. In addition to its traditional bookstores, Barnes & Noble operates 674 college bookstores. Its shares fell 26 cents, or 2 percent, to $12.91 in midday trading. They have traded in a 52-week range of $10.45 to $25.