MILWAUKEE — With sales continuing to decline and losses mounting, retailer Bon-Ton Stores Inc. said Thursday it plans to close at least 40 stores through 2018.

Bon-Ton (BONT), the parent company of Boston Store, Younkers and other department store brands, has lost money for the last six years, and said Thursday it lost $44.9 million in its fiscal third quarter as sales fell 7.6%. Through the first three quarters of 2017, Bon-Ton lost $135.4 million.

Closing 40 stores would represent the shutdown of about a sixth of Bon-Ton's 260 department stores, furniture galleries and clearance centers in the U.S.

Bon-Ton is an anchor tenant in most major shopping malls in Wisconsin, and like many retailers, has struggled amid competition from online retailers and reduced visits to malls by consumers.

The company, which has dual headquarters in Milwaukee and York, Pa., didn't immediately say which stores it plans to close.

In a statement Thursday, William Tracy, Bon-Ton's chief executive, said the company, which carries high debt, also would seek to develop "a sustainable capital structure to support the business.

"While results in the third quarter fell short of our expectations, we are taking more aggressive actions to fuel improved performance as well as strengthen our financial position," Tracy said. "We are also focused on cost reductions through the continued rollout of our profit improvement initiatives. In addition, we expect to implement a significant store rationalization program and plan to close at least 40 locations through 2018. This will enable us with moving forward with a more productive store footprint and redirecting capital expenditures toward investments designed to drive sales growth."

Tracy said those steps, along with working on the capital structure, are aimed at bringing about "consistent financial performance over the long term."

"With our new merchandising initiatives in place and more seasonable November weather, we are already seeing a positive comparable store sales trend and believe we are well-positioned for a successful holiday season," Tracy said.

In addition to Boston Store and Younkers, Bon-Ton operates department stores under the brand names Bergner's, Bon-Ton, Carson's, Elder-Beerman and Herberger's.