Capturing Methods and Marking Tools
To estimate population size and growth trends, individuals can be captured, marked and re-captured after a period of time.
There are many capturing methods and marking tools that can be used, depending on the species. These should be as harmless to the individuals as possible.
For example, nets and (non-deadly traps) are usually a good choice. Manual capture can also be performed, but most species are difficult or catch or the chase can be very stressful.
Regarding marking tools, these vary from subcutaneous chips and acoustic pingers, to less invasive leg bands and neck collars.