What are the techniques for measuring population size?

There are four techniques for measuring population size: the mark-recapture method, length-age relationships, age distribution, and growth increment analysis. The mark-recapture method involves capturing and marking a sample of animals, then recapturing a portion of them and using statistical calculations to estimate the size of the entire population. Length-age relationships involve using the size of an animal to predict its age, assuming that older animals are larger, but this method is limited by species-specific growth patterns and sexual dimorphism. Age distribution involves analyzing the age structure of a population to estimate its size, and growth increment analysis involves counting the rings on structures such as otoliths or scales to determine the age and size of an animal.