A white zee-bat

 is a Sunless Sea Random Event.

Story description
A zailor has grown fretful and disobedient, reluctant to go on deck, even in port. "There's a white zee-bat watching me up there. Salt's messenger. Salt's got its eye on me. I'll never see home again!

Trigger conditions
The Gods of the Zee: Stone, Storm and Salt ≤ 0, Crew ≥ 2 Something Awaits You ≥ 1 ≤ 50, Random Chance: 1%