Mitsui O.S.K. Lines Ltd., the world's largest merchant fleet operator, will reduce its expansion plans by 50 ships as worldwide demand for sea cargo shrinks.

The company will retire older vessels, giving it a total fleet of 1,150 at the end of March 2013, compared with a previous plan for 1,200, company spokesman Kenji Yoshimura said, citing President Akimitsu Ashida. The Nikkei financial newspaper reported the reduction earlier.

Mitsui O.S.K. and rival Nippon Yusen K.K., Japan's biggest shipping line by sales, are reducing their plans to increase their fleets after the Baltic Dry Index, a measure of commodity-shipping rates, tumbled 92 percent last year. Nippon Yusen said last month it will cut its expansion plans by up to 60 vessels.

Nippon Yusen now plans to ease its fleet growth plan by as many as 100 ships, the Nikkei also reported Wednesday. Nippon Yusen spokesman Suguru Uchida declined comment on the report.

Mitsui O.S.K. had 874 ships at the end of last March, while NYK had 776.