Spatial associations between lotic fish, macroinvertebrate prey and the stream habitat: a multi-scale approach

We adopted a multiscale approach to examine the spatial relations between stream fish, macroinvertebrate prey, and habitat characteristics in a boreal stream. The study site was divided into 279 cells, and abundances of brown trout and Arctic bullhead were quantified at each cell. Depth, water velocity, substrate size and aquatic vegetation were measured, and benthic samples collected, at each quadrat. Shaded contour plots showing the spatial distribution of selected variables within the sample space were produced and fish distributions were superimposed on these plots. High-density patches of trout and bullhead were in separate sections of the riffle, and bullhead were closely associated with their benthic prey, especially semisessile macroinvertebrates. Semivariograms were produced for two variables, water depth and density of semi-sessile invertebrates. There was spatial dependence, especially in the density data, at lags shorter than 2 metres. Kriging was then used to create maps displaying the spatial patterns of the variables within the sample space. We believe this kind of multi-scale sampling strategy combined with standard geostatistical tools and statistical modeling will prove valuable in the study of aquatic consumer-resource interactions.