Which of these would not be a problem for a mark-recapture experiment?marked organisms are easier to

Which of these would not be a problem for a mark-recapture experiment?

marked organisms are easier to

capture

high mortality between surveys

immigration

marked animals spread throughout the population

A biologist is studying turtles. On the first trip she captures and marks 15 turtles. On the second trip she captures 40 turtles; 10 of these are her marked. What is her estimate of the population size?