Evaluation, harvesting and management of fluctuating stocks

Empirical data show that fish stocks fluctuate considerably and also sustain changes over periods of decades without a commercial fishery. These fluctuations are affected by environmental anomalies and by a fishery. Single-species population dynamics approaches and maximum sustainable yield (MSY) concepts are no longer sufficient for evaluation and management of fishery resources; holistic ecosystem simulations are coming into use. The "natural" fluctuations of the stock biomasses have periods of 4 to 7 years and magnitudes of 35% to 80% of equilibrium biomasses. To cope with such fluctuations, stocks should be managed on an annual basis. Increased efforts and accuracy of resource surveys are also required. The main technological problems of fisheries caused by fluctuating stocks are: 1) increased flexibility in fishing fleets (multipurpose vessels and gear); 2) flexibility in processing and marketing; and 3) more effective utilization of discards (bycatch).