A short story about a boy who was the son of a "normal" woman and a vaguely human denizen of the deep

Question

I read this Fantasy short story more than 20 years ago, in a collection.

There are two main characters, one is a "normal human" marine biologist. A dozen years or so before the events in the story, he went to some small island (IIRC in the Caribbeans) to study the fauna of the coral reef which surrounded it. There he met a boy that, on land, could almost pass for a normal human, but for his slightly webbed hands. But in the water, slits would open to reveal gills that allowed him to dive deep and for a long time. The boy was clever, could read and write, and knew a lot about marine biology. His mother was a normal native of that island who was somehow impregnated by a creature that came out of the ocean, never to return to the land.

Year after year the relationship of the biologist with the boy deepens and eventually they write a scientific paper together. But the webs on the hands increase in size. In the events of the story itself, the webs are much bigger than on the first meeting, and the mother of the boy tells the biologist that her son spends more and more time underwater. Her son, now a fully grown man, tells the biologist that he has written detailed notes about their common research so the latter can write a second paper and that himself must now dive for ever.

I don't remember the end well. I think the biologist tries to follow him as if he could survive in the water, gets a glimpse of his friend's father (who has two legs, not a fish tail, but is still some kind of "merman", hence the tag "mermaids") and is brought back to the beach before he drowns.

Answer 1

In the Islands by Pat Murphy. I read it in the anthology The Year's Best Science Fiction, First Annual Collection.

The marine biologist is Nicholas C. Rand, referred to in the story as Nick. The boy is Morris.

As you say, Nick had been know Morris for years, and in the story Nick notices the webbing between Morris's fingers is growing. Morris tells him:

“My dad, he came to the harbor; and we swam together. I’ll be going with him soon. Look.” Morris held up one hand. The webbing between his fingers stretched from the base almost to the tip of each finger. The light from the overhead bulb shone through the thin skin. “I’m changing, Nick. It’s almost time.”

They first met when Morris saved Nick from an attacking shark, and that's when Nick saw the gill slits:

The shadow that intercepted the shark was neither elegant nor efficient. In the beam of the flashlight, Nick could see him clearly: a small boy dressed in ragged shorts and armed with a shark billy. This one exploded when he struck the shark, and the animal turned with grace and speed to cruise away, heading for the far side of the reef. The boy grinned at Nick and glided away into the darkness. Nick saw five lines on each side of the boy’s body—five gills slits that opened and closed and opened and closed.

At the end Nick meets Morris's father:

Morris’s father turned in the water to look up at Nick and Nick read nothing in those inhuman eyes: cold, dark, dispassionate. Black and uncaring as the eyes of a shark. Nick saw Morris swim down and touch his father’s shoulder, urging him away into the darkness.

And as you say they save Nick from drowning, then Morris says goodbye for the last time:

He felt a cold arm around his shoulders. He coughed up water when the arm dragged him to the surface. He coughed, took a breath that was half water, half air, coughed again. Dark water surged against his mask each time the arm dragged him forward. He choked and struggled, but the arm dragged him on. One flailing leg bumped against coral, then against sand. Sand scraped against his back as he was dragged up the beach. His mask was ripped away and he turned on his side to retch and cough up seawater.

Morris squatted beside him with one cold webbed hand still on his shoulder. Nick focused on Morris’s face and on the black eyes that seemed as remote as mirrored lenses. “Good-bye, Nick,” Morris said. His voice was a hoarse whisper. “Good-bye.”