Complex sentence: During the months of April and May, the vessels are not allowed into the sea due to the fishes' reproductive season, and are instead moved to dry-land and are repaired, painted, and refreshed in the vessel-building yard.
Split into simpler sentences: During the months of April and May, the vessels are not allowed into the sea due to the fishes' reproductive season. During these months vessels are moved to dry-land and are repaired, painted, and refreshed in the vessel building yard.