Difficulties in projection in future stock change
Ziro,Suzuki, National Research Institute of Far Seas Fisheries-
In the stock assessment, it is commonly attempted to make future projection of the stock change based on the information obtained from the stock analyses using data up to as recent as possible. Usually, the projected trajectory of the stock size is shown with a broad band of confidential limit around the average stock sizes at each time series.
This is due to existence of a lot of uncertainties scientists cannot account for quantitatively in the models such as unexpected sudden changes of recruitment by environmental factors. Theoretically, any trajectories are possible if they are within this broad band and important thing to know is there is only one true track no one knows. However, this obvious logic is not necessarily well understood even for professional scientists, and perhaps for many administrators who are in charge of management of the fisheries resources. Therefore, it is common that the projected trajectories are awfully different from the actual trajectories estimated using data that become available some time later period. The gap between the projected and actual track of the stock change become larger and larger as the projected years become longer and longer, say 20 years in the future that has been often used for long lived species like bluefin tuna. I wonder if scientists are skeptical enough to accept possibility that the true trajectory could even be outside of the broad range of confidence limits.
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