In a dynamic bio-economic multi-cohort analysis of fishing for a long lived species there can be a significant terminal value problem. The way this problem is dealt with can have a significant bearing on optimal policy recommendations. In this study, a bio-economic model of the Southern Bluefin tuna fishery was specified to determine optimal harvests over planning periods of different length. In each case zero prices were assumed for fish stocks left over. It was found that optimal harvest levels can be affected if the planning period chosen for the model is not long enough to make the influence of the assumption of zero prices for leftover stocks negligible. Model parameter values, initial stock conditions and the policy controls all can have a significant influence on the choice of an appropriate length of the planning period. Apart from increasing the length of the planning period while maintaining the assumption of zero prices for leftover fish stocks, positive price estimates for leftover fish stocks can be used to provide end conditions on prices of leftover fish stocks.