Mer maid mothers never quite become accustomed to the whales taking their children at birth. Their breasts still swell and harden with milk; their scales still dull with grief. Their life mates (male, female, or otherwise) attempt to comfort them only to be beaten back by razor sharp claws and fins as hard as steel.
the mothers eventually leave their pods in search of their children. They call out to them with the same whale songs their whale mothers sang to them when they were small. They dive deep (but only so deep, heeding the crazed glint in their mother’s eyes that told them to stay away, never leave the light completely) and furiously push down the tiny voice in the backs of their minds that tries to remind them that their own mothers never found them before it was time. Their own mothers, who were half mad by the time their children were returned to them.
the whales plan it this way. They know that the mothers will teach their young things that only the land-dwellers, in their madness, normally have access to. These lessons will keep the pod strong. The fear instilled will keep them from diving too deep, building too far.
It will ensure the leviathan sleeps on.