COS 137-1 - Nearshore fish abundance varies with armor extent

Abstract: Coastal nearshore marine habitats play an important role for many culturally and economically significant fish species. Within these areas, shallow water habitat and submerged aquatic vegetation offer opportunities to fishes for feeding and avoiding predation. Yet not all nearshore habitats are equal and fish distribution on a fine scale is influenced by a mosaic of biophysical factors like distance to shore, depth, and prey availability. On a broad scale, however, fish distribution may be influenced by the cumulative effect of other shoreline features. Evidence suggests that shoreline armoring modifies adjacent beaches to negatively influence some fish species, by way of reducing shallow water habitat and insect prey communities. My research aims to explore whether there is a threshold of armoring at which there is a detectable decrease in fish abundance, at various spatial scales. To accomplish this, we collected fish abundance data in the nearshore at sites throughout the southern Salish Sea, Washington in April-September for four years. Initial analysis has shown that presence of armoring influences the distribution of Pacific Herring and Surf Smelt, while Pacific Salmon abundance varies according to other factors, like presence of vegetation. We expand on this work by discussing how patterns evolve across hierarchically nested spatial scales. This work will inform shoreline restoration prioritization by advancing our understanding of the circumstances which cause armoring to have an impact on nearshore fish populations and to maximize habitat restoration potential in urban estuaries.