Ocean harvests have plateaued worldwide and many important commercial stocks have been depleted. This has caused great concern among scientists, fishery managers, the fishing community, and the public. This book evaluates the major models used for estimating the size and structure of marine fish populations (stock assessments) and changes in populations over time. It demonstrates how problems that may occur in fisheries datafor example underreporting or changes in the likelihood that fish can be caught with a given type of gearcan seriously degrade the quality of stock assessments. The volume makes recommendations for means to improve stock assessments and their use in fishery management.