Consequences of climatic change for water temperature and brown trout populations in Alpine rivers and streams

Abstract

Twenty-five years of extensive water temperature data show regionally coherent warming to have occurred in Alpine rivers and streams at all altitudes, reflecting changes in regional air temperature. Much of this warming occurred abruptly in 1987/1988. For brown trout populations, the warming resulted in an upward shift in thermal habitat that was accelerated by an increase in the incidence of temperature-dependent Proliferative Kidney Disease at the habitat's lower boundary. Because physical barriers restrict longitudinal migration in mountain regions, an upward habitat shift in effect implies habitat reduction, suggesting the likelihood of an overall population decrease. Extensive brown trout catch data documenting an altitudinally dependent decline indicate that such a climate-related population decrease has in fact occurred. Our analysis employs a quantitatively defined reference optimum temperature range for brown trout, based on the sinusoidal regression of seasonally varying field data.

Climate and land-use changes affecting river sediment and brown trout in alpine countries—a review

“…Recent studies have shown that air temperature in the alpine regions is changing more rapidly than in other regions of the northern hemisphere and the global average (Lebensministerium 2003;Beniston 2006;Hari et al 2006). From data analyses of twelve stations in Switzerland in the period 1864-2000, Begert et al (2005) found a rise in temperature by 1.1°C and 0.6°C per century in northern and southern side of the Alps, respectively, (Table 1) and the warming occurred mainly during autumn and winter months.…”

“…However, more recently , changes in air temperatures occurred in spring and summer at lower altitude stations (<700 m a.s.l. ; Hari et al 2006). Rising air temperature is reflected in coherent rise in water temperatures (up to +1.1°C) in streams both in the lowlands and in the foothills of the Alps, but the changes are less obvious in alpine streams influenced by glaciers and/or hydropower stations (Hari et al 2006;Matulla et al 2007).…”

“…; Hari et al 2006). Rising air temperature is reflected in coherent rise in water temperatures (up to +1.1°C) in streams both in the lowlands and in the foothills of the Alps, but the changes are less obvious in alpine streams influenced by glaciers and/or hydropower stations (Hari et al 2006;Matulla et al 2007). Rising water temperature has shifted the thermal habitat for fish communities upwards up to 130 m (Hari et al 2006;Matulla et al 2007) and might affect fish health and reproduction (see discussion below).…”

“…: April, >1,200 m a.s.l. : May; Hari et al 2006). Since the rise in temperature due to climate change occurred particularly in autumn and winter seasons, it directly influences reproduction and egg development.…”

“…Since the rise in temperature due to climate change occurred particularly in autumn and winter seasons, it directly influences reproduction and egg development. Accordingly, the emergence of brown trout fry from the gravel beds is predicted to have advanced by 2.8-5.6 days per decade in alpine rivers (Hari et al 2006).…”