Flexi Says: Shark populations have declined significantly in recent decades, and many shark species are now in danger of becoming extinct. Scientists estimate that shark populations are declining at the rate of about 100 million individuals per year. Most of this decline is due to human activities, including overfishing. The demand for shark fins is the primary cause of shark overfishing. A significant number of sharks also get caught in nets as a byproduct of fishing for other fish species. Sharks are being killed by these activities faster than they can reproduce.