Part 1 Fundamentals of the theory of fishing, illustrated by analysis of a trawl fishery: theoretical methods in the study of fishery dynamics; the basis of a theoretical model of an exploited fish population and definition and definition of the primary factors; mathematical representation of the four primary factors; a simple model giving the annual yield in weight from a fishery in a steady state. Part 2 Some extensions of the simple theory of fishing: recruitment and egg produciton; natural mortality; fishing mortality and effort; growth and feeding; spatial variation in the values of parameters - movement of fish within the exploited area; mixed populations - the analysis of community dynamics. Part 3 Estimation of parameters: relative fishing power of vessels and standardization of commercialo statistics of fishing effort; estimation of the total mortality coefficient (F + M) an dthe maximum age, t2; separate estimation of fishing nd natural mortality coefficients; recruitment and egg-production; growth and feeding. Part 4 The use of theoretical models in a study of the dynamics and reaction to exploitation of fish populations: application of population models of Part 1; application of population models of Part 2; principles and methods of fishery regulation; requirements for regulation of the North Sea demersal fisheries. Appendices: tables; list of symbols and their definitions; derivation of indices of total European fishing effort on North Sea plaice and haddock during the pre-war period.