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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THE ROLE OF SMALL STREAMS 2
Coastal Streams
  • 8/ The role of coastal streams, i.e. small streams that directly enter the sea or an estuary, is not well understood. There are a large number of these, and it is probable that significant populations of sea trout lead an essentially marine life, only entering coastal streams briefly to spawn. Estimates of smolt production for the streams entering Strangford Lough demonstrate the potential contribution made by coastal streams to sea trout production. As mentioned above, there is evidence of 0+fry moving into brackish water; this has also been reported on Orkney and on the Sussex Ouse.  It was suggested that salinity was important here, and that while fry could tolerate brackish water they could not survive in sea water. The economic importance of coastal sea trout rod fisheries is growing, and it is possible that a substantial proportion of the sea trout targeted in these fisheries was produced in such streams. The workshop agreed that more research is needed on the role and importance of coastal streams in contributing to sea trout numbers at sea 
Robert Rosell: Strangford Lough - a sea trout system due to stream size?
Fishless Streams and Invertebrate productivity in small streams 
  • 9/ Even where very small streams are not populated by fish, they play an important role in a catchment and contribute significantly to overall biodiversity. They not only provide a direct source of invertebrates for fish, via downstream drift, but constitute potential refuges for invertebrates in cases of pollution downstream. 
  • 10/ In her presentation Mary Kelly-Quin summarised what is known of invertebrate productivity in small streams in Ireland. Although a considerable amount of macroinvertebrate sampling had been undertaken, this had generally been  in the context of assessing land-use impacts; only one study had specifically focused on headwaters.  Overall, small streams exhibited high heterogeneity in terms of their species complement, with typically over half of the macroinvertebrate species occurring in less than 5% of sites and less than 10 taxa  common to all sites. Moreover, small streams made an important contribution to biodiversity, with significant number of species found only in headwaters.  Only limited data on macroinvertebrate abundance were available, but it was clear that while abundance increased with distance from the stream source, heterogeneity declined. This might  mean that fish in small streams had access to a wider food base. The Workshop  agreed that research was needed to improve our knowledge of the macroinvertebrate communities and  productivity of small streams, and  of the contribution made by  aquatic and terrestrial macroinvertebrates from headwater streams  to salmonid diets. The use of stable isotope analysis for the latter should be explored.
Mary Kelly-Quinn: Macroinvertebrate communities in small streams in Ireland
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