SMALL STREAMS: Contribution to populations of trout and sea trout.
Report of a workshop held at Carlingford,  Co. Louth, Ireland on 27 and 28 November 2012
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CLIMATE CHANGE AND SMALL STREAMS
  • 14/  Ciaran Broderick gave a presentation outlining the results of the RESCALE (Review and Simulate Climate and Catchment Responses at Burrishoole) project, which explored the potential ecological, biological and physical impacts of climate change on the Burrishoole catchment, utilizing the detailed environmental data available for the catchment. Data for the catchment had been compared with projections derived from different models, downscaled to a catchment level. The data had shown an increase in average seasonal temperatures, in the frequency of high temperatures and of heavy rainfall events. The combined projections suggested an increase in mean temperature over the period 2070-2099 of 1.7 ˚C, 1.8 ˚C, 1.7 ˚C and 2.2 ˚C (relative to the period 1961-1990) for winter, spring, summer and autumn respectively; moreover, the observed temperature data up to 2008 exceeded all the projections. The projections also suggested an increasing tendency towards a more seasonal rainfall regime, with this trend becoming more pronounced as the century progressed; and winter rainfall was projected to increase by 13% from the 2050s onwards, accompanied by a decrease of 10% in summer rainfall amounts. This was likely to lead to significant changes in flow regimes. Overall, seasonality in our climate would become increasingly pronounced. 
Ciaran Broderick: RESCALE - review and simulate climate catchment responses at Burrishoole
  • 15/  In discussion it was noted that small streams were particularly vulnerable to the impacts of climate change. Increased water temperatures are likely to pose particular problems.  There is evidence that these are affecting egg growth, with reduced times to hatching (although this could be being offset by later spawning). Relatively limited increases in temperature have been shown to affect juvenile growth and survival, and there is also evidence that higher temperatures reduce  survival rates among ranched salmon. There is a need for data on the effect of higher temperatures on energetics and on marine survival. Overall,  trout have a narrower range of optimal temperatures than salmon,  and it is possible that increased in-stream temperatures will serve as a driver for increases in levels of  anadromy. 
  • 16/  Climate change is also likely to lead to more extreme conditions, with more floods and droughts; the impact of these will be accentuated by the limited resilience of small streams .It was noted that work was needed on how algae, plants, invertebrates and fish would survive and on their ability to adapt;  interfaces between small and larger streams and small streams and loughs would be critical as refuge areas. Climate change would also increase the risks posed by invasive species, disease and parasites. 
  • 17/  The workshop concluded that it was important to record and map the impact of climate change on small streams, including cumulative impacts, using appropriate indicators, and that there was a clear need for national repositories of climate change information.  It was pointed out that in Ireland a great deal of relevant information was held in the National Biodiversity Data Centre (www.biodiversityireland.ie/).  It was also necessary to bear in mind that there is evidence for the existence of microclimates within catchments, so extrapolation of data from particular sites needed to be done with caution. 
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