At about 14:30 Alaska daylight time, a Cessna 337B lost power shortly after takeoff from the Seldovia Airport. The pilot and his passenger were seriously injured. The pilot told investigators that he had parked the aircraft about three days before the accident with the main tanks about half full. While making his preflight inspection the day of the accident, he noticed that the fuel gauges indicated the tanks were about one quarter full. He did not visually verify the fuel level in the plane, but planned to make a short flight to Homer to purchase fuel. He took off and, at about 500 feet, both engines began to run rough. He tried to turn back to the runway but didnt have sufficient altitude, so he made a forced landing on a tidal beach. During the landing, the airplane hit trees and landed hard. An Alaska State Trooper reported that both the left and right main fuel tanks were dry.