Fish stocks can collapse suddenly and without warning, placing significant economic stress on the fishers who depend on that stock. To improve management of fisheries, scientists look for hints that collapse is pending. A new study led by Dr. Vasilis Dakos and Secure Fisheries’ Dr. Sarah Glaser, published by the British Royal Society Interface, shows the strength of nonlinearity in fish populations can be a key indicator that the population is about to collapse from fishing pressure. Nonlinearity describes whether population ups and downs are smooth or chaotic. This study advances technical progress that should help improve governance and conservation of fisheries.