Risk/opportunity:(from the Climate Change Risk Assessment for Scotland 2012):
Cross-cutting freshwater risks • BD5 Species unable to track changing climate space

Narratives: Water quality and availability

SCCAP theme: Natural environment

SCCAP objectives:
N2: Support a healthy and diverse natural environment with capacity to adapt

Latest figures

Location

Mean abundance (fish ha-1) 2007/08

Loch Builg

1.2

Loch Doon

0.9

Loch Eck

0.0

Loch Girlsta

129.3

Loch Insh

205.9
Trend
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At a glance
  • Lake fish are physically restricted from shifting their range in response to changes in habitat suitability, making them particularly vulnerable to changing ‘climate space’.
  • The abundance of monitored Arctic charr populations, a cold water specialist with particular conservation value, is showing an overall decline with particular climatic vulnerability at the southerly end of their distribution.
  • Whilst management can do little to limit climate-induced changes in water quality, by reducing manageable non-climate pressures it may be possible to preserve viable populations at these sites.

Changes in thermal gradients as a result of climate change necessitate associated range shifts in populations of species, particularly those which either have a narrow thermal tolerance, or those already on the edge of their thermal range. Geographic range shifts are prevented when habitats and ecosystems are effectively spatially isolated as is the case for many lakes.

Freshwater fish are directly affected by changes in temperature as they cannot thermoregulate physiologically, and are therefore reliant on being able to move to areas with appropriate temperatures. Lake fish are limited in this movement by geographic boundaries, making them particularly susceptible to changes in thermal gradients, and making them ‘ideal sentinels for detecting and documenting climate-induced modifications of freshwater ecosystems’ (Jeppesen et al., 2012).

Arctic charr (Salvelinus alpinus) have the most northerly distribution of any freshwater fish, with the UK lying towards the southernmost limit of the distribution of this cold water specialist. Scotland is a stronghold for Arctic charr within the British Isles and 258 Scottish lochs are known to contain this species (Maitland et al, 2007). They are also a conservation feature in five Sites of Special Scientific Interest (Lochs Eck, Insh, Builg, Girlsta and Doon), and their conservation value is reflected by their addition to the United Kingdom Biodiversity Action Plan (UKBAP) Priority Species List in 2007 (SNH, 2014). Charr populations in the five SSSI lochs form the basis of the indicator.

Mean abundance in four out of the five surveyed lochs show a significant decline over the period (see Table 1 and Figure 1). In two of these SSSIs (Loch Eck 2007, Loch Doon 2008), the status of Arctic char is now classified by Scottish Natural Heritage as ‘Unfavourable declining’ according to Site Condition Monitoring (SCM).

Table 1 Arctic charr abundance estimates (Winfield et al, 2010)

Location

Mean abundance (fish ha-1)

Significant trend (P <0.05)

2003/4

2007/8

Loch Builg

4.9

1.2

¯

Loch Doon

2.0

0.9

¯

Loch Eck

1.6

0.0

¯

Loch Girlsta

31.5

129.3

  

Loch Insh

457.8

205.9

¯

Figure 1 Arctic charr abundance estimates (geometric means with 95% confidence limits). The significance of observed changes is given within each graph (Winfield et al, 2010)

 

Relatively little was known about Arctic charr distribution and biology a few decades ago and new populations are still being discovered. However, at least 12 populations of Arctic charr in Scotland are known to have become extinct since they were recorded, though this number may be much larger since many sites have not been examined in recent years. Most of the known Scottish losses have been in south and central Scotland (Maitland et al, 2007), though some of these are documented as being as a result of acidification (SNH, 2014).

 

Given the temperature requirements of Arctic charr, there is a ‘strong reason to expect a significant negative impact of climate change on this species’ (Winfield et al, 2010). The population ranges of cold-specialists, like the Arctic charr, will likely shift towards higher latitudes or altitudes, and may become locally extinct at the warmest edge of their current distribution ranges (Jeppesen et al, 2012).

Site Condition Monitoring reports for the two Arctic charr features now classified as ‘Unfavourable declining’ (Loch Eck and Loch Doon) identify a number of non-climate drivers contributing to pressure on these populations. Whilst management of these sites can do little to limit climate-induced changes in water quality, by reducing manageable non-climate pressures (e.g. minimising disturbance due to draw-down of water, reducing impact from neighbouring forestry, and management of invasive species), it is possible that viable populations will be preserved at these sites.

 

The two most southerly sites (Loch Doon and Loch Eck) are the two SSSIs where the status of Arctic charr has been classified by SNH as unfavourable. Loch of Girlsta, the only loch to show an increase in charr abundance, is by far the most northerly location (see Figure 2).

Figure 2 Location of SSSIs where Arctic charr are a conservation feature

Climate warming has been shown to result in complex changes in fish assemblage[1] structure due to both the direct effects of temperature as well as indirect effects operating through pressures such as eutrophication, water level changes, stratification,  salinisation and the favoured spread of invasive species. A number of other, non-climate drivers have also been identified as potentially contributing to changes in charr population and distribution including, afforestation, lake engineering, exploitation, aquaculture and introductions of charr of different race, stock or type (SNH, 2014).

Plotting population decline against a measurement of climate change vulnerability for each lake (based on water body latitude, altitude and mean depth), Winfield et al (2010) lends support for the theory that climate change is a significant factor in the decline of this species in the UK (Figure 3).

Figure 3 The relationships between climate change vulnerability ranking and population decline rankings for 1990 onwards. Data is for lakes across the UK, including the five Scottish SSSIs (derived from Winfield et al, 2010)

Whilst vulnerability to climate change cannot be seen as the only pressure on these populations, there is mounting evidence that it is a significant contributory factor in the continued viability of this cold-water specialist.

[1] ‘Fish assemblage’- fish that occur together in a single place, such that they have at least a reasonable opportunity for contact with each other

Data is currently only available for a few lochs, and the presumption of the presence of charr in Scottish Lochs is, in many cases, based on old records alone, with very little known about the current status.

Whilst there is growing evidence that the decline of Arctic charr in Scotland can be attributed, in part at least, to climate change, present evidence is still relatively weak (Winfield et al, 2010).

Jeppesen, E., Mehner, T., Winfield, I. J., Kangur, K., Sarvala, J., Gerdeaux, D., Rask, M., Rask, M., Malmquist, H. J, Holmgren, K., Volta, P., Romo, S., Eckmann, R., Sandström, A., Blanco, S., Kangur, A., Ragnarsson Stabo, H., Tarvainen, M., Ventelä, A.-M., Søndergaard, M., Lauridsen, T. L. & Meerhoff, M. (2012) Impacts of climate warming on the long-term dynamics of key fish species in 24 European lakes.  Hydrobiologia 694, 1-39. DOI:  10.1007/s10750-012-1182-1.

Maitland, P.S., Winfield, I.J., McCarthy, I.D., & Igoe, F. (2007) The status of Arctic charr Salvelinus alpinusin Britain and Ireland. Ecology of Freshwater Fish 16, 6–19.

Scottish Natural Heritage.http://www.snh.gov.uk/about-scotlands-nature/species/fish/freshwater-fish/charr/. Accessed June 2014

Winfield, I.J., Hateley, J., Fletcher, J.M., James, J.B. Bean, C.W. & Clabburn, P.  (2010) Population trends of Arctic charr (Salvelinus alpinus) in the UK: assessing the evidence for a widespread decline in response to climate change. Hydrobiologia 650, 55-65.  doi: 10.1007/s10750-009-0078-1.

Ian Winfield, Centre for Ecology & Hydrology