Fish-predator interactions                      WTT position and advice                Further information


Fish-predator interactions

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.

WTT position & advice

For further information behind the WTT's advice, please click the links below:

Avian predation information paper           Avian predation information sheet

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. A WTT presentation to an Environment Agency Wales Conference in May 2012 outlined some of this work and described a range of methods to create varied and complex habitat:

Predators, Prey and the WTT

Fishery interests can additionally deter predators through a range of scaring and/or exclusion techniques (see appendix A below), 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.

Direct control (culling) of species whose impact is deemed to be impossible to otherwise mitigate is used by all kinds of institutions with many and various ends. For example, deer are culled by forestry, farming and conservation organisations for different reasons when their numbers reach levels that impact on other objectives. This happens despite the existence of tree guards, deer fences and other deterrents and avoidance tactics. It is, therefore, not a surprise when calls come for permission to control species predating on fish populations which, like crops and wood anemones, also have economic and conservation value. When, unlike deer, the predators are themselves locally abundant but nationally or internationally scarce and therefore protected, the moral arguments for culling are further complicated.

It is for exactly these circumstances that we have regulation, and it is for the regulator (government and its agencies) to take all the evidence of local and national predator impacts into account alongside all the alternative means of protecting prey populations when making locally sensible decisions about direct control. Decisions on culling species that have national protection because of their wider conservation status should be a local debate informed by evidence; our only suggestion is that this should be with a regulator who has been given the discretion to take a locally informed view whilst maintaining a national and international conservation perspective.

Further information

The booklet Protecting Your Fishery from Cormorants describes a number of methods aimed at deterrence or reducing the success of cormorant feeding (see

In the case of some persistent piscivorous birds, shooting to kill remains an option, when licensed through appropriate government agencies, such as Natural England (, Welsh Assembly Government (, Scottish Natural Heritage (, the Dept of the Environment for Northern Ireland ( and in Ireland, the National Parks and Wildlife Service (

The study 'Between Fisheries and Bird Conservation - The Cormorant Conflict' contains very recent (2013) and pertinent information at a pan European scale.

The WTT attended the International Otter Survival Fund Otters (IOSF) and Fisheries Conference in Edinburgh on 7/11/2012. To read the conference proceedings, please cick the following link:

International Otter Survival Fund - Otters and Fisheries Conference Report (with kind permission of the IOSF).

Invasive Crayfish - This paper shows the benefits of crayfish trapping for the biodiversity of a river but highlights that any trapping needs to be intensive in order to work.