Spatial variation in environmental characteristics of Atlantic salmon (Salmo salar) rivers

Rivers and streams occupied by anadromous Atlantic salmon (Salmo salar) occ ur across a diverse array of landscapes. This article describes the general ecology of these rivers and streams, including many of the physical and bi ological variables that are important characteristics of all lotic systems. For analytical purposes, the geographic range of Atlantic salmon rivers is divided into dye regions, based on geomorphology and climate. The physical habitat available to anadromous Atlantic salmon is diverse. The geology va ries from granitic bedrock to volcanic and glacial substrates, which influe nce a broad array of other ecological variables, ranging from water chemist ry to catchment morphology (e.g., river length). Flood regimes and system h ydrology are dependent, as expected, on climate. Many of the catchments rec eive substantial precipitation in the form of snow; rivers in four of the f ive regions experience primarily spring freshets. Aquatic temperatures are also variable, representing close to the full range of thermal tolerance of S, salar, with lows just above 0 degrees C in the northernmost latitudes t o summer highs in western Europe approaching 25 degrees C. Most rivers are best characterized as oligotrophic with relatively low annual primary produ ctivity. However, physical factors such as availability of suitable spawnin g and rearing habitat, as well as aquatic temperature and flow regimes, may drive anadromous productivity. In general, most of the rivers have been mo dified by flow regulation and many suffer from impacts related to other ant hropogenic disturbances, principally riparian forest clearing for agricultu re, forestry, and urban development. We conclude that the rivers and stream s occupied by anadromous Atlantic salmon are diverse across the species' ra nge and have been heavily impacted by anthropogenic disturbances.