Overfishing is a situation where one or more fish stocks are reduced below predefined levels of acceptance by fishing activities. More precise definitions are provided in biology and bioeconomics.It occurs when fish are caught faster than they can reproduce. . Many marine scientists now believe that overfishing is the biggest human impact on the world's oceans. A recent study in the prestigious journal Science showed that overfishing makes ocean ecosystems more vulnerable to harm from other human impacts like pollution.