Abstract

The estimation of mortality in a stock-rehabilitation program is critical to the evaluation of the efficacy of that program. We present here an overview of a generalized model for estimating mortality rates of the benthic marine gastropod Strombus gigas based upon movements of individuals within an x:y array. The model assumes linear movements of individuals in random directions. We used this model to estimate mortality in field-released hatchery conch. Individually tagged conch were distributed uniformly within a 20 m x 20 m array. Subsequent surveys determined x:y coordinates of individuals within the grid, and individual movements were derived from these data. The negative binomial distribution best represented movements of the population and was used to estimate the probability of emigration of individuals from the grid. A probability matrix was developed that consisted of values which represented the probability of emigration of individuals located within specific cells in the array. Missing individuals were assigned a value representing the probability of emigration. Natural mortality was calculated by subtracting the estimated emigrants from the total missing conch. To the best of our knowledge, this model presents a new approach for estimating mortality for slow-moving, benthic marine species.

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