Range Shifts from Climate Change Across Three Western Rivers

Rising temperatures have produced shifts in the geographic distribution of species, but most evidence comes from terrestrial and marine ecosystems.  We examined changes in the distribution of 16 native species and 2 naturalized salmonids in three rivers in Colorado, USA: the Cache la Poudre, Big Thompson, and St. Vrain rivers.  Our analysis spans several decades, during which there was a pronounced warming trend in mean annual air temperatures.  Upstream range limits across species shifted up to 11 river km.  Changes in the downstream limits of species were more modest.  Upstream and downstream range shifts were generally consistent with expectations of climate tracking based on thermal guilds; however, a minor portion of species showed unexpected downstream shifts.  We will discuss the range shifts in these species in relation to species’ detectability during historical sampling and barriers to fish movement.