In mark-recapture, 100 fish were marked. Later, 150 fish were captured, of which 25 were marked. Population estimate = ?
Using the Lincoln–Petersen relationship, the marked fraction in the population is equated to the marked fraction in the recapture sample: M/N ≈ R/C. Solving gives N ≈ MC/R, where M is the initial marked release, C is the total second capture, and R is the number of marked recaptures. Substituting M = 100, C = 150, and R = 25 yields N = 100 × 150/25 = 600 fish. The logic is also intuitive: one-sixth of the second catch is marked, so the original 100 marked fish are inferred to constitute one-sixth of the population. Reliable estimation requires a closed population between occasions, durable and
Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 9