What was more surprising was how precisely this rule seemed to play out. When Sheldon and his colleagues organized their plankton samples by orders of magnitude, they found that each size bracket contained exactly the same mass of creatures. In a bucket of seawater, one third of the mass of plankton would be between 1 and 10 micrometers, another third would be between 10 and 100 micrometers, and the final third would be between 100 micrometers and 1 millimeter. Each time they would move up a size group, the number of individuals in that group dropped by a factor of 10. The total mass stayed the same, while the size of the populations changed.

Comparing these pre-1850 estimates to the modern-day models told a very different story. The models suggest that the biomass of fish larger than 10 grams and all marine mammals has shrunk by more than 2 billion metric tons since 1800. The very largest size classes appear to have experienced a reduction in biomass of nearly 90 percent since 1800. Many of the big fish and mammals that used to populate the ocean simply aren’t there anymore.

Some of the fish stocks being overexploited include Japanese anchovy, Alaska pollock, and South American pilchard. “I think we are moving towards a world where the default is not a natural ecosystem in which everything is as you had it before there was human exploitation and intervention,” says Kaschner.

Humans Have Broken a Fundamental Law of the Ocean – Mother Jones