Firefly Squid

Each spring, typically from March to June, enormous numbers of firefly squid migrate from deep water toward the surface to spawn, and the particular underwater geography of Toyama Bay, on the Sea of Japan coast, funnels them into a concentrated area close to shore. A deep submarine canyon runs almost right up to the coastline there, and currents push the spawning squid up along it, so that vast numbers end up near the surface at once, and when disturbed by waves, nets, or each other they flash their light organs, turning stretches of the bay and the beach an eerie glowing blue at night. The phenomenon is famous enough that the area is a designated natural monument and a significant local tourist attraction.

The firefly squid produces light through bioluminescence, a chemical reaction in specialised organs called photophores, in which a light-emitting molecule reacts with oxygen and an enzyme to release energy as visible light with essentially no heat. It uses this light in several ways, most importantly for counter-illumination camouflage, matching the dim light filtering down from the surface with light from its own underside so that it does not appear as a dark shape to predators looking up from below, and it may also use flashing light patterns to communicate with other squid, to startle predators, or to attract or confuse prey.

Despite the dramatic scale of its spawning displays, an individual firefly squid is small, only about 7 to 8 centimetres long, roughly the length of an adult finger, making it one of the smaller squid species. Its modest size is part of why the mass spawning is so striking, since it is the sheer number of tiny glowing animals gathered together, rather than any single impressive individual, that produces the effect of an entire bay lighting up, and it also means the species sits fairly low in the ocean food web, serving as prey for a range of larger fish, squid, and marine mammals.

Yes. Like many squid species, the firefly squid has a short lifespan of only about a year and reproduces just once, at the end of its life. After the spawning migration into shallow coastal waters, females release their eggs and the adults, having exhausted their energy reserves on the migration and reproduction, die shortly afterward. This is why the beaches around Toyama Bay are frequently strewn with the bodies of spent firefly squid during and after a spawning run, and why the spectacular displays are an annual, seasonal event tied to the single generation reaching maturity each year.