There are plenty of fish in the sea, as the saying goes. But how many? New research suggests that our previous estimates of fish abundance were off by a factor of at least 10. According to a study published in February in the journal Nature Communications, the total mass of fish in the ocean is about 10 times greater than thought.
The study strictly concerned fish that live 200 to 1,000 meters (656 to 3,280 feet) below the surface. These “mesopelagic” fish make up the vast majority of fish in the sea–95 percent of all fish biomass, by some estimates.
This study doesn’t have much relevance for the issue of over-fishing, which is an enormous and still growing problem, since the species targeted most by fishermen like bluefin tuna live near the surface. By and large, it doesn’t make economic sense to go after these mesopelagic fish (at least yet), though there are some exceptions.
The study was quite an undertaking, entailing a journey of some 32,000 nautical miles through the world’s oceans, between the 40th parallel north and south. Fish abundance in the twilight zone (another name for the dark region inhabited by these animals) was estimated by an echo sounder, which bounced waves off fish bodies.
Prior to now, there have been discrepancies in models of nutrient transfer between the shallow and deep ocean, discrepancies which the authors suggest can be explained by the sheer abundance of fish, which feed closer to the surface at night and then return to the deep at night, where they poop. One should not underestimate the importance of fish excrement.
A final fun fact from the study: bioluminescent bristlemouths (in the genus Cyclothone) are “likely the most abundant vertebrate on earth.” You read that right: the Earth’s most common backbone-blessed animal is (probably) a light-producing fish that lives most of its life in the darkness of the deep sea. Amazing!