PORTLAND — The Boston Red Sox and Portland Sea Dogs have agreed to extend their Player Development Contract for an additional four years, keeping the Red Sox Double-A affiliation in Portland through the 2018 season.

The Sea Dogs originally entered into a contract with the Red Sox following the 2002 season, ending a nine-year affiliation with the Florida Marlins. The Sea Dogs and Red Sox last extended their affiliation in January 2011, taking the contract through the 2014 season.

“As we prepare for our 20th season of Sea Dogs baseball we are thrilled to announce this new agreement,” said Bill Burke, chairman of the Sea Dogs. “It is an honor to be associated with the Boston Red Sox, one of the greatest franchises in professional sports, and we are pleased to let our incredible fans know that this relationship will continue well into the future.”

Red Sox’ Director of Player Development Ben Crockett added: “The Portland Sea Dogs and the Burke family have been tremendous partners in the development of Red Sox minor league players who have played at Hadlock Field. We are excited to extend our relationship and look forward to continued success in the future.”