Huge communities of migrating deep-sea marine life are to be blamed for a baffling, low-frequency humming sound that comes from the ocean when the creatures swim to and from the surface during feeding.

The University of California, San Diego assistant research biologist Simone Baumann-Pickering, has made a discovery, answering a long-standing query. NPR reported that the source of the hum has vexed marine biologists for years. They were very well aware that the sound wasn't constant with whale calls or other marine mammals, like dolphins, communicating.

However, now using high-sensitivity undersea audio recordings, Baumann-Pickering said that it’s animals like fish, shrimp, squid, and jellies surviving in the ocean’s mesopelagic zone, an area 200 to 1000 meters underneath the surface, that are responsible for the sound.

In the mesopelagic neighborhood, creatures live deep down in a dark region, a world where the sun hardly ever shines and lacks a bounty of food. Thus, every night, in the safe darkness, they take a risk of going on to the surface where food is more abundant.

On reaching top (or back down) the hum nearly 3 to 6 decibels louder as compared to ocean background noise, kicks in.

Baumann-Pickering said in a statement, “It’s not that loud. It sounds like a buzzing or humming, and that goes on for an hour to two hours, depending on the day”.

The reason behind the sound is so far an open query. However, as per Baumann-Pickering, it may be an indication to the entire group to make a move up to the surface or back down.

Though it’s neat to think that the animals also communicate and give signals to each other but there could be another, a less high-minded explanation for the hum. It might be the case that the creatures pass gas, when their swim bladders regulate their buoyancy.