Realizing the basis for overfishing and quantifying fish population dynamics

ICES was established in part because of serious concerns that North Sea fish stocks were being overfished, although great difficulties were experienced with defining overfishing. Hjort provided a new synthesis of the causes of fluctuations in landings by introducing age compositions of stocks and explaining the fluctuations by yearclass variations. This explanation opened up revolutionary new possibilities for stock predictions. There is a close connection between solving the problem of defining overfishing and the development of fish population dynamics theory and models. In the 1930s, an operational definition of the term overfishing was made possible by Hjort’s theory of optimum yield using population growth models, and this was applied by Graham to North Sea fisheries. Later developments of stock-recruitment theory and yield-per-recruit models made it possible to define the terms growth overfishing and recruitment overfishing. In the early days of fish population dynamics modelling, a particular problem was the mathematical treatment of mortality. Baranov had solved this problem in 1918 by defining instantaneous mortality rates, but his contribution was not recognized until the late 1930s by Graham and others, and Ricker appears to be the first to have fully understood Baranov’s paper. The analytical approach by Baranov and Ricker was further developed in the pioneering work of Beverton and Holt in 1957. The influence of the work of Beverton and Holt was enormous. Their models became standard tools in stock assessments and laid the basis for the development of virtual population analysis (VPA) and modem catch prediction methods. Andersen and Ursin formulated a multispecies extension of Beverton and Holt’s theory which became a key reference for later work with muitispecies models. Also, quantification of the effect of a fluctuating physical environment on fish stocks has recently received more attention. Quantifying multispecies and environmental effects and developing stock assessment models capable of utilizing all sources of data that may contain information on the stock are the main challenges of today.

Article from Marine Science Symposia Vol. 215 - 100 years of science under ICES. To access the remaining articles please click on the keyword "MSS Vol. 215".