Over the past century, the biomass of predatory fish in the world’s oceans has declined by about two thirds, according to fisheries scientists. In the voids left by the cod, halibut, salmon, and tuna are increasing populations of forage fish, which are short-lived and vulnerable to environmental change such as ocean waters that are warming and becoming more acidic in response to global climate change.

“What this doesn’t boil down to is the sea is suddenly full of sardines and anchovies and other small things that we like to eat,” Villy Christensen, an ecosystem modeler at the University of British Columbia in Vancouver, Canada, said. “It is to a large extent small fish that we don’t eat that have benefited; because sardines and anchovies, those are fisheries … we keep fishing those.”