Temporal and spatial variability of the demersal fish biomass size spectrum on the Scotian shelf

Data from the Canadian Department of Fisheries and Oceans summer groundfish survey on the Scotian Shelf were used to construct annual biomass size spectra for the period 1970-1991. Three studies are presented each exploring a different aspect of biomass density distribution by size for demersal fishes on the Scotian Shelf:; Chapter 1 examines large amounts of data on fish size distribution over time and at various scales. It was found in this study that temporal constancy of the fish biomass size spectrum is a property of the system which emerges only at large enough spatial scales. The exact scale at which this constancy emerges is dependent on the body size of the organisms being studied. Chapter 2 uses the model developed by Thiebaux and Dickie (1992, 1993) to fit a curve to empirical size spectra. Ecologically reasonable parameters were derived from this fitting. As a method of analysis, this fitted curve was regarded as a hypothetical distribution and deviations of an individual years' data from this distribution were examined. Chapter 3 attempts to relate the deviations encountered in the Chapter 2 analysis to the dynamics of species groups. When combined species size spectra were broken into species groups it appeared that a third order of size scaling in aquatic ecosystems might be revealed.