Historical patterns of fish stocks

Fish stocks may be divided into four classes according to their natural patterns of variation: steady, cyclical, irregular and spasmodic. To be successful, fishery assessment and management must take these patterns into account. This may involve some modifications of traditional methods, for example the existence of large irregular fluctuations in recruitment can make management by catch quota more difficult than some other approaches. Spasmodic stocks (e.g. some anchovy and sardine stocks with long periods of scarcity interspersed with periods of very high abundance) raise particular problems.