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The mer are very mysterious to the surface dwellers, as they almost never communicate, and humans who fall off ships are usually taken below, if gotten to before they drown, and changed into mer, so they cannot return. There are some sad songs about exiles and so forth, but little is known about mer life.
Mer humans seem to know the indigenous water beings, coexisting in harmony. There have been mers known to attack enemies like Norsunder but it is very rare.
They also coexist with the giant creatures of the deeps. At one time there was war between these and humans in ships, until it was agreed that fishing would be confined to egg-layers, and not to deep-water mammals. After that, there was no more attacking of ships, though the Venn mages for a time were enjoined to find a way to enchant and thus harness the giants of the deep, an experiment that as often turned against the mages as benefited them, and so it was abandoned when the Venn mages had other troubles.