Underwater habitat is a key factor in determining the interaction between fish predators and their prey. Weed cover and other submerged structures are widely used by fish to reduce the risk of predation from pike and other predators. It has been found that the survival of prey species increases, and the growth rate of predators decreases, as vegetation density becomes greater. The extent to which this might apply to cormorant/fish interactions is less well established, but there is good reason to believe that similar factors will operate. Cormorant numbers tend to be highest on inland waters over the winter, when natural cover for fish (e.g. weed beds) is at its lowest level and when fish swimming speeds are least (due to the lower water temperatures). Fish refuges therefore provide fish with additional cover and reduce their accessibility to cormorants at a period of the year when the fish are particularly vulnerable to predation.

Given that cormorants will be able to swim faster than most small fish in winter, refuges should not be viewed as ‘bolt holes’. Instead, it will be necessary for any refuge structures to attract and ‘hold’ fish, while providing protection from predators. It is not yet possible to provide definitive refuge designs, but it is evident that the key features would be:

         the provision of overhead cover,
         the incorporation of ‘structure’ to mimic natural habitat features,
         a means of excluding cormorants.

Overhead cover provides shading and this has been shown to attract fish and give them an enhanced ability to detect oncoming predators. ‘Structure’ might include artificial weed, brushwood bundles, branches, Christmas trees or submerged pipes. It is clearly necessary to exclude predators from the refuge areas, and this could best be achieved by surrounding fish attractants with 10cm mesh netting to make them ‘cormorant-proof’. One successful option, providing both structure and cormorant-proofing in a single design, has been the use of small ‘reefs,’ constructed by joining together coils of mesh made of sheep wire (see Case study 1).

The potential benefits of using refuges are likely to vary with the fish species present and from site to site. Initial evaluation suggests that refuges might be most suitable for fish such as roach and perch, but a range of freshwater species may benefit. The features of a particular fishery are also likely to be important in deciding whether refuges will be effective. For example, the size of the water and the extent of existing natural cover will need to be considered. Refuges may be of particular value in relatively featureless sites, and, in such instances, positioning may be less critical. However, where some existing cover is available, enhancing natural features may be better than positioning refuges elsewhere. Thus, placing refuges adjacent to emergent vegetation may well be more beneficial than providing alternative refuge areas in open water, well away from any existing cover. Alternatively, protecting existing natural refuge areas, such as marginal emergent vegetation, through the use of fenced and covered enclosures may represent an effective refuge option (see Case study 2).

There will, of course, be a number of constraints and practical limitations to using refuges. These structures may cause fish to aggregate unnaturally, a particular problem where match fishing is practised. There is also the risk that, without appropriate identification, tackle may become snagged, with the resulting loss of gear becoming a hazard for wildlife. It will also be important to ensure that the refuge structures themselves do not pose a risk of entanglement for fish and other wildlife. However, correctly designed to prevent bird ingress, refuges should provide the fish with some protection and help reduce expensive stock loss. It should also be borne in mind that refuges could be used on a seasonal basis, being deployed only for the winter period, when fish are most vulnerable and there are usually fewer anglers on the bank.

Research is currently continuing into the potential benefits of fish refuges for inland fisheries and the information provided here will be updated as new information comes to light. As previously indicated, refuge designs can vary and there is unlikely to be a single best option for use at all sites. In some instances, it may be preferable to enhance or protect existing natural refuge areas, such as emergent vegetation, whereas, elsewhere, installing new artificial structures will be preferable. Refuge designs will also vary and, in many instances, the devices will be constructed on site by volunteers using materials readily available locally from builders’ merchants. However, floating rafts incorporating pre-planted reed beds are available ‘off the shelf’ and further details can be obtained from:

         Spirex Aquatec
            Tel: 01527 821601
            Web: www.spirexaquatec.com

         MMG Civil Engineering Systems Ltd / A.G.A. Group
            Tel: 01553 617791 / 01428 609056
            Web: www.mmgces.co.uk / www.agagroup.org.uk

Refuges can be elaborate constructions, but this is not always the case. The establishment of any weed/reed bed or merely installing branches, small diameter pipes or any other ‘obstruction’ in the corner of a fishery will help to buffer predation effects.

We would warmly welcome feedback from any angling clubs and fishery managers who may have practical experience or relevant comments on the design, installation and efficacy of fish refuge structures.