Fortuity Disguised as Fisheries Management: The Case History of Fortune Bay Herring

Abstract

The population dynamics of a stock of spring-spawning herring in Fortune Bay, Newfoundland, are described in relation to exploitation patterns, management strategies, and environmental variability. Biomass levels increased substantially during the late 1960's as a result of the recruitment of several strong year-classes that were pulse-fished by a purse-seine fishery. The resulting high fishing mortality rates caused a rapid stock decline in the early 1970's that was associated with an increase in the partial recruitment rate of the younger age-groups as well as an increase in the catchability coefficient of the purse-seine fleet. The combination of these classical changes resulted in a substantial overestimation of stock abundance and recruitment levels that was not corrected until an alternative series of catch rates and partial recruitment estimators were used to fine-tune population assessment. Environmental factors, rather than spawning stock size, were shown to explain a significant fraction of recruitment variability. Alternative fishing strategies such as the F0.1 and surplus production concepts were simulated and shown to be less efficient in extracting biomass yield than pulse-fishing. It is concluded, therefore, that management regimes whose objectives are promulgated on the basis of stock rebuilding, stock stability, and enhanced recruitment through protection of the spawning stock are unlikely to succeed (except fortuitously) for herring populations such as those in Fortune Bay due to the dominant controlling influence of environmental variability. For such herring stocks the most appropriate long-term management strategy that could be supported on biological grounds would be a minimum size limit established at or above the length of 50% maturity.