A number of animal species predate wild trout — mammals (e.g. otter, mink), birds (e.g. cormorants, sawbill ducks) and other fish (e.g. pike, larger trout). Predation is just one of a complex of factors impacting on wild trout populations; for many populations the effects of unsympathetic land use, poor in-river habitat, low water quality and water quantity and poor river management regimes will be of greater significance.
WTT recognises that predation can be problematical for fish populations and for fishery interests. Since the 1970’s, there has been an increase in the inland over-wintering population of cormorants and an increase in the geographical range of goosanders, though there is evidence in 2012 that cormorant numbers have stabilised or even slightly decreased.
Unequivocal, scientifically-derived information establishing direct relationships between wild trout and predator populations in aggregate is lacking and difficult to obtain, especially for rivers. However there is anecdote from various parts of the British Isles indicating effects of intense, localised predation pressure from piscivorous birds.
We believe that the primary focus for fishery interests in tackling predation problems should be the creation and maintenance of complex and varied habitat that gives fish a much greater chance of avoiding predators.
Fishery interests can additionally deter predators through a range of scaring and/or exclusion techniques, though these may be more applicable to small stillwaters rather than rivers or large lakes and their efficacy relies on persistence and variety of scaring method.
As with all (re)introductions of species, the case of the Eurasian beaver (Castor fiber) is generating much heat in the UK media from many angles: conservation, fisheries, natural flood management to name but a few. There are now several trial schemes in place spanning from the Tamar in Devon to Tayside in Scotland.
The majority of questions we at WTT get asked regarding beavers involve passage issues for wild trout around dams. While any ecological interaction between two species is inherently complex and influenced by locality and flow régime for example (in this particular case), we should remember that beaver and trout have co-evolved for millennia and coexist in many locations throughout Europe. However, the landscape throughout much of the UK where they might formerly have coexisted, prior to the extirpation of beaver, has changed considerably and is now subject to a suite of environmental pressures from humans that could influence the outcomes of any current interaction. We have reviewed the scientific literature and numerous reports from other organisations. Click on the links below to read the summary paper or full paper:
Note – neither report considers management options in any detail. At the time of our review, the publication of The Eurasian Beaver Handbook: Ecology and Management of Castor fiber was imminent and it contains the most comprehensive overview of management issues by one of Europe’s leading experts, Róisín Campbell-Parker. Interim management advice is available from Scottish Natural Heritage.
Former WTT Conservation Officer for the South West region, Mike Blackmore, sits on the Fisheries Forum for the Devon Wildlife Trust Beaver Trial. The role of that forum is to ensure that fish and fisheries stakeholders (e.g. angling clubs) are engaged throughout the study and have the opportunity to ask questions and raise any concerns. Mike wrote a very interesting article on the River Otter Beaver Trial for us, available here.