The spawning routes of the Palau Siren are scheduled to coincide with one of the most unique marine phenomena in Micronesia: the reproductive aggregations that occur monthly in the waters of Palau linked to the lunar cycle. Beyond the main event, the itinerary explores the landmarks of the Rock Islands Southern Lagoon, a UNESCO World Heritage Site, featuring walls, current channels, caves, and wrecks from World War II. Blue Corner, German Channel, and Ulong Channel complete an itinerary with a distinctly pelagic character, home to reef sharks, mantas, Napoleon wrasse, and large schools of fish.

The focal point of the trip is the spawning of the bumphead parrotfish (Bolbometopon muricatum), which gathers in the days leading up to the new moon. At dawn, hundreds, even over a thousand individuals (some exceeding a meter in length) concentrate over the shallow part of the reef. Males clash their prominent foreheads to assert dominance, change color, and the aggregation releases their gametes in a synchronized ascent toward the surface. This is regarded as the largest concentration of this species on the planet.