How many fish are there in the sea?
This is the entry on this page with the worst-known answer, and pretending otherwise would be dishonest. The commonly repeated figure of 3.5 trillion has no strong provenance. What is measured is biomass rather than headcount: mesopelagic fish — the small lanternfish and bristlemouths of the twilight zone — were revised upward around 2014 from about 1 billion tonnes to perhaps 10 billion tonnes on the strength of better acoustic surveys, a tenfold change in a single decade. Divide an uncertain biomass by an uncertain average fish mass and the uncertainty compounds.
How the figure is arrived at
Ship-mounted echosounders measure how strongly the water column scatters sound; that scattering is converted to biomass using a target-strength model for fish swim bladders. The swim-bladder assumption is where the tenfold revision came from. Trawl catches calibrate the acoustic figures but under-sample fast-swimming fish badly.
How confident it is
- Low estimate
- 3,000,000,000,000
- High estimate
- 100,000,000,000,000
- Spread
- 33.3× between the bounds
Other living things and the natural world counts
- How many people are there in the world? about 8.2 billion
- How many grains of sand are there on Earth? roughly 7.5 quintillion on the world's beaches
- How many ants are there in the world? about 20 quadrillion
- How many trees are there in the world? about 3 trillion
- How many insects are there? about 10 quintillion
- How many species are there? about 8.7 million
- How many people have ever lived? about 117 billion
- How many drops of water are there in the ocean? about 27 septillion
- How many species are endangered? more than 45,000 assessed as threatened
- How many bees are there in the world? roughly 2 trillion managed honey bees
- How many birds are there in the world? about 50 billion wild birds
- How many bacteria are there on Earth? about 5 nonillion
- How many earthquakes are there each year? about 20,000 located a year — around 55 a day
- How many chickens are there in the world? about 26 billion alive at any moment
Common questions
- How many fish are there in the sea?
- somewhere between 3 trillion and 100 trillion — nobody knows
- How is that estimated?
- Ship-mounted echosounders measure how strongly the water column scatters sound; that scattering is converted to biomass using a target-strength model for fish swim bladders. The swim-bladder assumption is where the tenfold revision came from. Trawl catches calibrate the acoustic figures but under-sample fast-swimming fish badly.
Related pages
- How many people are there in the world? about 8.2 billion
- How many grains of sand are there on Earth? roughly 7.5 quintillion on the world's beaches
- How many ants are there in the world? about 20 quadrillion
- How many trees are there in the world? about 3 trillion
- How many insects are there? about 10 quintillion
- How many species are there? about 8.7 million
- How many people have ever lived? about 117 billion
- How many drops of water are there in the ocean? about 27 septillion
- How many stars are there in the universe? Space and the universe
- How many countries are there in the world? Things people built
- How many bones are in the human body? The human body
- How many stars are there in the Milky Way? Space and the universe
- How many atoms are there in the universe? Space and the universe
- How many galaxies are there? Space and the universe
Sources
- Typical range compiled from manufacturer specifications — At One Place