Narrator: This is Science Today. Years of commercial harvesting of larger, faster growing fish are leading to subsequent generations of increasingly smaller and slower growing fish. Chris Darimont, a postdoctoral researcher in environmental studies at the University of California, Santa Cruz, says that's because the fish are undergoing an evolutionary process that Darwin described as natural, or adaptive, selection.
Darimont: You can picture a gill net, for example. The mesh sizes is a certain diameter and anything smaller than that diameter can swim right through, survive and reproduce. This is a simplification, but it's instructive. Something a little larger gets stuck in that mesh size of that diameter, doesn't survive, does not reproduce, does not pass on those genes that code for faster growth or larger size. So, you can imagine that after many generations of targeting these large individuals, of taking so many of a population, that the subsequent generations get increasingly smaller and slower in growth.
Narrator: The good news, Darimont says, is many fisheries are now urging the avoidance of taking the largest fish. For Science Today, I'm Larissa Branin.