Adaptive Probing Strategies for Age-Structured Fish Stocks

This paper examines methods of preventing a stock of fish from being held far below its optimal size. Such sustained overexploitation could arise because the model used to manage the stock poorly represented the stock dynamics, because there are significant errors in the estimates of stock abundance, or because there is insufficient contrast in catch and fishing mortality to generate reliable estimates of the productive potential of the stock. We develop a method to correct for biases due to errors in estimates of abundance and show that this correction does improve estimates of productivity, but not sufficiently to enable a manager to recognize the presence of overexploitation. We demonstrate that the management system must generate significant contrast in catch and effort, and once the contrast is generated the managers can easily find near optimal abundance of the stock. With reasonable levels of contrast even very simple surplus production models will perform well when managing complex age-structured fish stocks.