Climate Change and the European Water Dimension - Agri ...

values, with an upper limit of 30°C during the warmest season. An increase in
temperature might first suppress the populations of burbot, salmonids, and
coregonids and favour the preponderance of cyprinid species.
With climate change, the greatest losses in cold-water species would occur in the
southern borders of a species’ natural range, where the minimum temperatures are
closest to thermal tolerances. Many species are particularly temperature-sensitive
during spawning. An EPA study based on modelling of thermal conditions in lakes
assuming a doubling of CO2 levels, found that the region faces a 50 to 100%
potential loss of habitat for brown, brook, and rainbow trout, cold-water species that
are highly valued by anglers.
The projected increases in winter temperature could adversely affect the spawning
and embryonic development of a number of fish species in the Atlantic Region. The
eggs and embryos of most fish tolerate a much narrower range of temperatures than
their juveniles and adults (Elliott, 1981). The most temperature sensitive fish in the
region are the whitefishes (Coregonus lavaretus) and the charr (Salvelinus alpinus).
These species are often called 'glacial relicts ' and are assumed to be land-locked
remnants of species that at one time migrated freely to and from the sea. The
current geographical distribution of these species is clearly influenced by temperature
(Wheeler, 1977; Maitland, 1977). Most of the lakes in which they thrive today are
cool, deep basins in the more mountainous areas of the U.K. Both species have an
upper thermal limit of 8 o C for their egg stage so many of these populations could be
endangered by the predicted increases in winter temperature.
The spawning performance of trout and salmon populations in the Atlantic Region
should not be adversely affected by the projected increases in winter temperature.
Increased spring temperatures could, however, stimulate early emergence when the
larvae would be smaller in size and might not be able to find enough food to survive.
The response of fish to warmer winters in Sweden's largest lakes Vänern, Vättern
and Mälaren is complex and not yet completely analysed. One study shows that
autumn spawners such as vendance (Coregonus albula) have difficulties in adapting
to warmer temperatures. The catch of vendance drastically decreased when lake ice
breakup was very early in the year (Nyberg et al. 2001).
The impact of global warming on freshwater fish will vary seasonally. The additional
temperature may provide growth benefits in winter, but may threaten fish populations
living towards the upper end of their thermal tolerance zone in (late) summer
(Morgan et al., 2001). Simulated global warming had little effect on the growth and
physiology of rainbow trout (Oncorhynchus mykiss) fed to satiation over much of the
summer. However, in late summer, when ambient water temperature was at its
highest, the addition of 2°C caused a marked inhibition of appetite and growth,
although this impact was not exacerbated by a reduction in food availability. In winter,
a change of temperature of +2°C stimulated metabolism, appetite and growth by
approximately 30 to 60%.
To a certain extent fish can acclimate to higher temperature. Rainbow trout exposed
to + 2°C had a slightly (0.2-1.0°C) but significantly higher lethal temperature than
those exposed to ambient temperature (Morgan et al., 2001).
The potential effect of climate change on average runoff in tundra regions is highly
uncertain (McCarthy et al., 2001), but if water levels decrease, connections between
tundra lakes could be severed. This would result in changes in community structure
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