Richard B. Deriso

A Markov movement model of yellowfin tuna in the eastern Pacific ocean and some analyses for international management

Abstract A movement model is developed to quantify the probabilities of movement for yellowfin tuna in the Eastern Pacific Ocean. The model specifies a probability transition matrix for the odds of a given-aged individual moving from one 5° 2 spatial stratum to an adjacent spatial stratum during each month. A novel feature of the model is the description of discrete movement with three parameters (velocity, diffusion, and direction) in a manner analogous to continuous movement models. A maximum likelihood approach is taken to estimate movement and catchability parameters for data obtained from tagging experiments. Yield-per-recruit analysis is a critical, though often neglected, tool required to evaluate the need for international management of tunas. A modified mean residence time calculation is shown which addresses some consequences of eliminating the harvest of smaller sub-optimal sized yellowfin tuna.