Eileen F. Skinner, Mercy Hospital’s longtime president and chief executive officer, has tendered her resignation effective March 31. Skinner’s resignation was announced Monday afternoon in a news release issued by Mercy’s parent organization, Brewer-based Eastern Maine Healthcare Systems. Skinner has been with EMHS since September 2002. During her tenure, Skinner oversaw the construction of a state-of-the-art hospital along the Fore River in Portland. A not-for-profit organization, Mercy is sponsored by the Sisters of Mercy of the Americas.