Exploring the Effects of Biases in Mark-Recapture Fish Abundance Estimation with Software Simulations

Two-sample mark-recapture sampling is a common method used to estimate fish abundance. The idea is to capture and mark fish in an initial sample. The fish are then released to mix randomly with the whole population. A second sample is obtained, and the number of marked and unmarked fish is recorded. The Chapman estimator uses the number of fish marked in the first sample, the total number of fish captured in the second sample, and the number of recaptured fish to estimate abundance. The assumptions are: 1) the population is closed, meaning no immigration/emigration, and births/deaths occur, 2) all fish are equally vulnerable to capture during each sample, meaning marking does not change fish behavior, and 3) marks are not lost/overlooked. Violations of the assumptions happen frequently, and examining bias when a combination of assumptions are violated is difficult. Therefore, we created a software that lets users simulate different violation scenarios and examine the resulting biases.