Spatial variance of mobile aquatic organisms : capelin and cod in coastal Newfoundland waters

Horne, John K. (1995) Spatial variance of mobile aquatic organisms : capelin and cod in coastal Newfoundland waters. Doctoral (PhD) thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (23MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

Patchy distributions of organisms are a long recognized attribute of terrestrial and aquatic ecosystems. Quantitative descriptions of spatial variance provide clues to processes that generate patchiness. In aquatic environments, greater effort has focussed on quantifying spatial variance in distributions of plankton than on quantifying spatial variance in distributions of mobile organisms. To evaluate the relative importance of biological and physical processes that generate variance, a theoretical framework was developed that combines demographic, growth, and kinematic rates in dimensionless ratios. Ratio values are then plotted as a function of temporal and spatial scale. Application of this technique identified kinematics as the dominant process influencing capelin (Mallotus villosus) distribution along the coast during the spawning season. -- Hydroacoustic distribution data of capelin and Atlantic cod (Godus morhua) were analyzed to examine how shoaling, schooling, and the aggregative response of predators contribute to the spatial variance of mobile, aquatic organisms. A characteristic scale of patchiness was not observed at the temporal scale of a single transect (ca. 1 hour) or at the scale of a survey (ca. 2 weeks). On average, spatial variance decreased slightly over intermediate scales (10 km - 0.5 km) and then dropped rapidly at smaller scales. Data manipulations and computer simulations demonstrated that shoaling potentially increases spatial variance at intermediate scales, and that schooling potentially reduces spatial variance at scales smaller than aggregation sizes. There was no evidence of an aggregative response by cod to concentrations of capelin throughout the analyzed scale range (20 m -10 km). This unexpected lack of spatial association between predator and prey was explained using estimates of foraging energetics to show that cod were not constrained by physiology to track prey during the capelin spawning season. -- Theoretical and empirical results of this study have increased knowledge of scale-dependent spatial variance in mobile, aquatic organisms and provided insight to the biological processes that potentially generate these patterns. Scale-dependent plots of spatial variance combined with rate diagrams can be used to evaluate the relative importance of biological and physical processes that influence organism dispersion as a function of spatial and temporal scale.

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