Modelling the response of size and diversity spectra of fish assemblages to changes in exploitation

In this paper we investigate whether single and multispecies fisheries models can be used to predict the response of size and diversity spectra of fish assemblages to changes in exploitation. Both types of models estimate that the slope of the size spectrum will steepen and the intercept will increase when fishing intensity increases, while the response of the slope and intercept of the diversity spectrum depend on the model used. The changes in the slope and intercept of the size spectrum are found to be proportional to the change in fishing intensity. The proportionality is insensitive to changes in natural mortality, but sensitive to changes in growth and to the relationship between stock and recruitment. The results agree well with results obtained from previous analysis of survey data from the North Sea and suggest that the slope of the size spectrum is a useful measure of fishing impacts. ? 1998 International Council for the Exploration of the Sea

[1]  Jake C. Rice,et al.  Patterns of change in the size spectra of numbers and diversity of the North Sea fish assemblage, as reflected in surveys and models , 1996 .

[2]  R. Jones,et al.  The use of length composition data in fish stock assessments (with notes on VPA and cohort analysis). , 1981 .

[3]  A. Lerner.  Some Theoretical Aspects , 1949 .

[4]  Stephen J. G. Hall,et al.  Fishing and the Ground-Fish Assemblage Structure in the North-Western North Sea: An Analysis of Long-Term and Spatial Trends , 1996 .

[5]  B. Gobert.  Size structures of demersal catches in a multispecies multigear tropical fishery , 1994 .

[6]  R. W. Sheldon,et al.  The Size Distribution of Particles in the OCEAN1 , 1972 .

[7]  A. Rijnsdorp,et al.  Changes in abundance of demersal fish species in the North Sea between 1906-1909 and 1990-1995 , 1996 .

[8]  J. Pope,et al.  A Comparison of Fish Size-Composition in the North Sea and on Georges Bank , 1988 .

[9]  S. C. Venema,et al.  Introduction to tropical fish stock assessment , 1992 .

[10]  S. Murawski,et al.  Multispecies Size Composition: A Conservative Property of Exploited Fishery Systems? , 1992 .

[11]  R. Gregory,et al.  Abundance and body size in British birds: reconciling regional and ecological densities , 1995 .

[12]  S. Cousins,et al.  Species diversity measurement: Choosing the right index. , 1991, Trends in ecology & evolution.

[13]  A. Magurran.  Ecological Diversity and Its Measurement , 1988, Springer Netherlands.

[14]  M. Hill.  Diversity and Evenness: A Unifying Notation and Its Consequences , 1973 .

[15]  S. C. Venema,et al.  Introduction to tropical fish stock assessment. Part 1 : manual , 1993 .