Seeking patterns of population variability from fish catch and stock biomass time series.
Many exploited fish stocks experience unexpected and large fluctuations as a consequence of climatic variability. It seems therefore inappropriate to manage these stocks by applying principles based on equilibrium assumptions. This study aims to establish a classification or typology of fish stocks to enable suitable management approaches to be matched to fisheries characterised by similar patterns of fluctuations. The approach used builds on previous attempts to classify fish stocks according to the patterns of variability in time series of catch or biomass. Fifty-one catch and biomass time series were decomposed into linear trend, short and long-term fluctuations. Parameters representing total variability and relative amount of short and long-term variations were used to classify stocks into categories, using cluster analysis. Six categories of stock were distinguished. A discriminant analysis was then used to ascertain if there was any link between the ecological features of fish stocks (e.g. growth, mortality, maximum size) and classifications according to patterns of variability. It can be concluded that few fish stock biomass or fishery catch time-series correspond to steady-state ideals. However, there is no strong statistical evidence for a general correspondence between different types of fish (e.g.. small pelagic species, large demersal stocks) and differing patterns and extent of variation in biomass or catch time series.
Marine Resources Assessment Group Ltd., London, UK, 36 pp.