“Beyond the Dead Reef,” by James Tiptree, Jr.
Appeared in The Magazine of Fantasy & Science Fiction, January 1983; won a 1983 Locus Award for best short story; collected in Tales of the Quintana Roo (Arkham House, 1986), which won a 1987 World Fantasy Award for best collection); appeared in PseudoPod 603, July 13th, 2018 (though not reprinted as text—perhaps there was a problem getting the rights)
A few thousand words
Interesting, but the initial buildup strikes me as long and not closely related to the main story (even though I love the murder plot), the monster is silly, and the moral at least borders on heavy-handed. Perhaps I’m reading it from the wrong era.
The framing comments on how unreliable the narrator is ought to undermine the story, it seems to me, but don’t. Is that typically the case? Are we wired to enjoy a good story regardless of what we think about the storyteller?