Spatial dynamics and interactions between coastal fish community functional groups in Lake Huron

Background/Question/Methods

Fish communities in the Great Lakes have been subject to a multitude of environmental changes in recent years, including rapid increases in the abundance of the double-crested cormorant, a fish-eating waterbird. However, the effect of this population expansion on coastal fish communities is poorly understood. A five year study was undertaken to investigate the spatial dynamics of coastal fish communities across the North Channel and Georgian Bay basins of Lake Huron, covering approximately 84 000 hectares. Hydroacoustic surveys of seven 400 km² grids with varying densities of double-crested cormorants were conducted from 2000-2004, while nearshore locations in each of the seven grids were quantitatively electrofished from 2001-2005. Hydroacoustic techniques yield spatially-explicit data on the density of different size classes of fish across a variety of habitats, while simultaneously collecting information about the structure of the habitat. Electrofishing yields more detailed information about species and individuals across both broad and fine spatial scales.

Results/Conclusions
Fish community composition and spatial dynamics differed markedly between the North Channel and Georgian Bay basins. Patterns of spatial aggregation of different size classes of fish tended to be coherent among sampling locations at night, but varied during the day. Additionally, after controlling for spatial autocorrelation, there were positive correlations between all size categories of fish during the day, but the strength of the relationship varied between different size classes and sampling locations. Together, these results suggest that the processes driving patterns of spatial distribution of coastal fish differ between the daytime and the night, as well as across large spatial extents. These results may be informative to our overall understanding of fish community dynamics in large lakes.