Earlier this year, I wrote about how the human obsession with size is reshaping the bodies of other species at an incredible pace. Unlike natural predators that cull the sick, weak and unfit, human fishermen prize the biggest catches and throw the smallest ones back in.
As a result, fish and other species harvested by humans are shrinking, often within a few generations, and are becoming sexually mature at an earlier stage. These changes are bad news for populations as a whole, for smaller individuals often have lower odds of survival and produce fewer offspring.
But David Conover from Stony Brook University has found a silver lining in this tale – selectively harvesting fish can lead to dramatic changes in body size, but these changes are reversible. Release them from the pressure of constant hunting, and some of the animals start to rebound to their previous state.
Conover spent ten years raising a commonly harvested species called the Atlantic silverside in six captive populations, each containing about 100 individuals. Every year, the fish produced a new generation and for five years, Conover would remove 90% of the fish, either by taking the largest ones, the smallest ones or randomly selected individuals. In every other way, the fish were all reared under exactly the same conditions. This constant upbringing ensured that any changes to their bodies would be the result of genetic influences rather than environmental ones.