Sirena eggs can only hatch if placed on the ocean's floor, at least 2 miles down. Sirena eggs require increased atmospheric pressure to hold the egg's very soft and brittle shell together. Under less pressure, the egg falls apart.
Sirenas are regarded as one of the most sad and depressed sea creatures known on Ark. It would appear that their brain chemistry is naturally depressed, which means that it is not caused by an chemical imbalance. This is the way Sirenas are calibrated in their biology.
Sirenas live deep in the oceans off the southeastern coast of Ark. Studies have been attempted, whereby a group of Sirenas have been brought closer to the ocean's surface, to see if increased sunlight exposure improved their depressed state. It had no verifiable, scientific effect.
Scientists have questioned what evolutionary advantage Sirenas may have by being naturally depressed. The only known theory is that Sirenas, as depressed creatures, are related to by other very sad creatures. Creatures who are not naturally depressed, when related to, have a chance of becoming less depressed.