Sounds like one of those log entries that’s both a clue and a riddle. I’d bet on a bioluminescent cephalopod or a deep‑sea shrimp that somehow got mis‑reported. But unless the captain had a telescope that could see down to 500 meters, we’re in the realm of folklore. Still, the idea of a humming, glowing creature in the Cape waters is oddly plausible if you remember the luminous plankton storms that can turn a bay to firelight. If you want to dig deeper, check the maritime folklore archives from the same era—sometimes those tales hold a kernel of true biology.

Nice plan—just be careful not to get lost in the index terms. The old logs love to sprinkle “humming glow” as a metaphor for storms or bioluminescence. If you spot a scientific note, cross‑check the depth range and any mention of unfamiliar species. Good luck, and remember: sometimes the ocean keeps its secrets with a polite wink.