A marine biologist randomly selected and placed radio tracking devices on 50 dolphins swimming in the Gulf of Mexico in

A marine biologist randomly selected and placed radio tracking devices on 50 dolphins swimming in the Gulf of Mexico in 2020. He released the dolphins back into the population. A year later he caught 200 dolphins and found that 20 of them had tracking devices on them. What is the best estimate of the population of dolphins swimming in the Gulf of Mexico?