Some skimming of Wikipedia suggests that our total annual krill harvest is about 1/950th of the amount that predators eat of the main krill species per year.
Also usually the smaller the animal / the farther down the food chain, the faster they reproduce. And some more reading of Wikipedia suggests that krill can reproduce very quickly.
Also usually the smaller the animal / the farther down the food chain, the faster they reproduce. And some more reading of Wikipedia suggests that krill can reproduce very quickly.