INTRODUCTION

The basic purpose of work on fish stock assessment is to provide advice on the combinations of gear and fishing effort that will provide sustainable yields from a stock. Technically, the status of an exploited stock may lie between being underfished (a combination of low fishing effort and large age or size at first capture) or overfished (when effort is high and size or age at first capture is small). Additionally, overfishing can progressively reduce recruitment to the fishery, leading to a long-term decline in catches. The actual catch that is taken from any fishing strategy will be proportional to the numbers of recruits to the fishery within the area under consideration. Recruitment rates will be determined by spawning stock biomasses, events in the pelagic phase, and post-settlement dynamics, but only the maintenance of spawning stock biomasses at prudent levels and the protection of nursery areas are realistically within the control of fishery managers.

FIRST STOCK ASSESSMENTS: 1890S–1950S

Stock assessments had their genesis in the late nineteenth century, when scientists first took note of the changes in fish stocks that were induced by fishing. Petersen (1892) observed modes in plots of the length-frequency distributions of various fish species and attributed these modes to successive year classes and noted their variability. Rings in otoliths and scales soon became firmly established as a means to estimate growth rates (Hoffbauer, 1898; Reibisch, 1899; Thompson, 1902).