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The potential use of fish refuges to reduce damage to inland fisheries by cormorants - VC0120

For centuries, cormorants and other fish-eating birds have been in conflict with, and persecuted by, fishermen because of the perception that the birds compete for and damage exploitable stocks of fish to the extent that fishery catches are reduced. Recent research (funded by MAFF/DETR/Environment Agency) on fish-eating birds in England and Wales, concluded that cormorants can have a major impact on some freshwater fisheries.

Fish-eating bird species are protected under UK and European legislation. There are provisions for killing or taking birds under licence for the purpose of preventing serious damage to fisheries, and where other satisfactory solutions are lacking. However, shooting is not possible at many locations due, for example, to the proximity of human habitation or the nature conservation status of a site. There is thus a clear need to identify alternative management measures that might reduce the interaction between these predators and prey and minimise the level of impact.

The introduction of fish refuges to fisheries has been identified as a technique that is expected to have low environmental impact and that may be practical, both in terms of cost and ease of application, for reducing losses of fish to cormorants. The use of such structures has therefore generated considerable interest amongst anglers, angling associations and conservationists, and refuges of varying design have started to be used at freshwater fishery sites in the UK. However, it is essential that refuges are effective if they are to be recommended as a management measure; refuges will therefore need to impact upon predator/prey interactions in such a way that prey (as a whole, or particular species) are made less available. Refuge designs thus need to be based upon the best understanding of fish behaviour and habitat preferences, and the underwater foraging behaviour of the birds.

In recognition of the need to enhance our knowledge about fish refuges, DEFRA agreed to fund a programme of work to evaluate this possible management option (Project VC 0114). This was originally put forward as a planned sequence of work, over four phases, with ‘break points’ to allow for consideration and re-evaluation between key phases; phases 1 and 2 were included in project VC0114. Phase 1 has been completed and phase 2 is due to finish in March 2002. In phase 1, a detailed, critical review of fish and cormorant behaviour, the response of fish to predators and the role and benefits of artificial structures (e.g. reefs and refuges) in fisheries was completed, as well as extensive consultation held with stakeholder groups. Subsequently, in phase 2, a number of preliminary investigations were carried out to test the attractiveness of a range of refuge designs to different species of fish. Further work under this phase will be carried out early in 2002 to assess refuge usage by fish and whether cormorant foraging behaviour is affected by the presence of refuges.

Less progress was made in identifying approriate refuge designs in Phase 2 than was envisaged, due partly to the foot and mouth disease epidemic (and consequent loss of fieldwork opportunities). While further work to investigate the attractiveness of particular structures for various fish species would be beneficial, it is felt that the emphasis of the work should now shift to assessing whether refuges will provide tangible benefits for fisheries. From a fishery manager’s perspective, this is the critical consideration and further delays in addressing this issue are likely to attract criticsm from stakeholders and would be unacceptable politically. The previous studies are considered to provide a sufficiently clear indication of the types of refuge design that are likely to be effective, and the most appropriate fish species to target, in taking forward these studies. It is envisaged that further evaluation of refuge designs would also be carried out alongside more applied field investigations to assess the effectiveness of fish refuges at reducing predation.

This proposal sets out a programme for taking forward the work to investigate the benefits, practicalities and logistics of deploying refuges in freshwater fisheries and to establish whether the use of refuges might offer an acceptable and effective technique for limiting losses of fish in general, or of particular target species, to cormorants. At present, evidence to suggest that refuges confer any benefit is largely anecdotal and further scientific investigation is required. It is also essential that any potential refuge designs are not only effective, practical (in terms of cost and application) and of low environmental impact, but that they are also acceptable to the fishery owners and anglers who will need to employ them. This will also require further investigation as part of this proposed roll-on programme.

It is envisaged that the proposed study would enable DEFRA to provide more comprehensive advice and guidance in relation to the potential benefits of deploying fish refuges for reducing predation by cormorants. This would be a direct benefit in the context of DEFRA’s wider responsibilities for managing the conflict between cormorants and inland fisheries.
The overall scientific objective of the work is to test whether appropriate underwater refuge structures can reduce the availability of prey and hence the foraging efficiency of cormorants to the extent that individual birds catch fewer fish, in total, or of particular ‘target’ species, at sites containing appropriate refuges, and/or choose to forage elsewhere. The work also aims to assess the acceptability of refuge structures to anglers and other water ‘users’. The work would be completed in two new phases, and is a logical extension to the work completed in Phases 1 and 2 in project VC0114:

Phase 3 Objective - Experimental trials

1. Carry out controlled experiments in paired ponds to assess whether the presence of refuge structures can significantly reduce loss of, or damage to, species of freshwater fish due to cormorant predation (CEFAS and CSL involvement).

Phase 4 Objectives - Field evaluation at fishery sites

2. Assess whether refuges have any measurable impact on fish stocks, catches or prey selectivity by cormorants at selected freshwater fishery sites (CEFAS responsibility).
3. Assess whether cormorant numbers and foraging efficiency are reduced at fishery sites where refuge structures are deployed (CSL responsibility).
4. Assess what effects refuges have on anglers, fishery managers and any other ‘users’ of the resource (CEFAS responsibility).

Ongoing Objectives - Further refuge evaluation

In addition to the above principal Objectives (1-4), it is anticipated that the proposed work programme would also allow further investigation of the effectiveness of different refuge designs (an aspect of the work of Phase 2 that was not fully addressed during project VC0114 due to unavoidable delays – FMD). This will, in the main, be achieved as part of the above studies. However, efforts will continue to be made to collate information arising from refuge deployment at other sites through liaison with the EA and fishery managers, supported, where appropriate, by brief field trials. It is envisaged that this is an area where the EA may be able to provide particular input.

5. Describe the extent to which different refuge designs are used by various fish species (CEFAS responsibility).
6. Collate information on refuge designs, and the evaluation of refuges (assessment methods used and any identified benefits), from other sites where refuges have been deployed (CEFAS, with possibly some CSL involvement).
Project Documents
• Final Report : The potential use of fish refuges to reduce damage to inland fisheries by cormorants   (7124k)
Time-Scale and Cost
From: 2002

To: 2005

Cost: £429,465
Contractor / Funded Organisations
Pest and Weed Control              
Pest Control              
Plants and Animals              
Wildlife Management              
Fields of Study
Wildlife Management