The large increase in cormorant populations across Europe over the past 30 to 40 years has resulted in widespread conflicts with different fishery interests because the sites where cormorants choose to feed are often those most valued by recreational anglers, commercial fishermen or fish farmers. The situation varies widely between countries and regions. However, where such conflicts occur, there may be benefits in taking management action to alleviate the damage that the birds are doing, or might do, to the fish stocks at particular sites.
Cormorant/fishery conflicts occur at a wide variety of sites and over varying geographic scales. As such, there is a continuum in terms of the size of water body at which conflicts can occur, and management activities might be considered, from small isolated ponds to large lakes, river catchments and coastal areas. This large variation in scale inevitably imposes different challenges for those seeking to resolve conflicts and reduce the degree of damage to fish stocks at different sites.
At a more local level (e.g. individual water bodies or discrete areas) management strategies typically seek to deter birds from feeding at a site and cause them to move to other less valuable feeding areas. This might be achieved through a range of non-lethal deterrents, shooting some of the birds to reduce numbers and aid scaring, or some combination of the two. These measures can also be applied over wider geographic areas, but management at such scales is likely to require some degree of co-ordination. For example, bird numbers in particular areas might be reduced through co-ordinated activities to prevent roost formation near sensitive water bodies containing valuable fish stocks. For many, however, reduction of cormorant numbers (population control) - e.g. through co-ordinated actions at breeding colonies - is considered necessary to reduce damage over broader spatial scales.
The following sections explore management measures in more detail. There are numerous management tools that can be used to limit the interaction between cormorants and fish. These can be aggregated into broad categories based on the way in which they influence the interaction between the birds and their prey. There are also important issues of geographical scale and it is important to distinguish between local management and wider population management – in terms of actions and likely outcomes:
These different approaches are described in more detail below, illustrated where possible with examples of where different techniques have been applied in practice. However, there are some important general considerations that need to be considered in applying any management techniques.
Before exploring the use of different possible techniques, there are a number of important issues that people should consider before contemplating the use of any management measures.
i. Legal issues
It should be remembered that cormorants, like all wild birds, are protected under the European Wild Birds Directive 2009/147/EC. This prohibits the deliberate capture, killing and disturbance of birds, and the destruction of their nests or taking of their eggs. However, the Directive allows Member States to make exceptions (technically, these are called derogations) to authorise the use of specific lethal or non-lethal measures where the birds are causing ’serious damage’ to a site, or when there is a reasonable expectation that this will happen, or for the protection of flora and fauna, and where there are no other satisfactory solutions. It should be noted that even non-lethal measures may contravene the provisions of Article 5 and/or 8 of the Birds Directive and, as such, require prior authorisation from the national competent authorities (a derogation issued in accordance with Article 9) before they can be used legally.
Additional cormorant protection legislation applies in most countries. Such legislation might regulate controls on factors such as: the techniques that can be used; the people permitted to use them; the timing or places where techniques can be applied; and the monitoring and reporting of results. Since local controls vary and may be subject to change over time, no attempt has been made here to detail national / regional regulations. Anyone planning to use lethal or non-lethal cormorant management measures is therefore advised to check the legal requirements with the appropriate national or regional authorities before proceeding to apply any technique at a particular place or time.
The European Commission has provided guidance on Article 9 of the Birds Directive which relates to the use of derogations and interpretation of ‘serious damage’ (see here ).
ii. Conflicts are often complex
Cormorant-fishery conflicts are usually complex – they are seen in different ways by different stakeholders, and they affect a range of fishery sectors across a variety of aquatic habitats. In addition, a wide range of factors other than cormorants impact on fish and affect fish stock sizes and fisheries (see here). Moreover, conflicts are also subject to change over time, partly because of the population dynamics of birds and fish, seasonal variations in other factors - particularly weather conditions - and the large-scale movements of the birds. Managing such conflicts is also complex and influenced by wide-ranging factors, making it impossible to provide specific one-size-fits-all recommendations for different fishery sectors or aquatic habitats that might instantly ‘solve’ any particular ‘problem’.
iii. The efficacy of control measures
There are, however, numerous tools available and ample evidence that these can prove effective in some places at some times. Identifying the most appropriate techniques will require careful consideration by individual stakeholders, as will the decision on whether or not efforts may need to be co-ordinated over a wider area.
The efficacy of control measures – that is their capacity to produce an effect – will depend on many factors, including a) whether birds are sedentary (remaining or living in one area) or migrating, b) the proximity of alternative foraging sites, c) the numbers of birds and food resources in the area, d) the features of specific sites, particularly the size or area of water, e) variations in cormorant numbers in particular areas, f) the type of fishery involved and its characteristics, and g) the size and nature of the fish populations at risk. The resources and time available to devote to using mitigation techniques and the associated costs (outlay versus losses) will also have a bearing on the use and efficacy of control measures.
Those faced with managing conflicts are strongly encouraged to experiment with different techniques, particularly where these have proved to be effective at comparable sites and in similar conditions, and to be creative in devising mitigation programmes to best suit their individual needs. An overview of considerations relevant to managing cormorant/fishery conflicts is available here.
Information on the large number of techniques that can be used to manage cormorant/fishery conflicts has been compiled as part of the INTERCAFE COST Action. This information has been published as the ‘INTERCAFE Cormorant Management Toolbox – methods for reducing cormorant problems at European fisheries’. The full report can be downloaded here; summary details of the various different groups of tools with links to appropriate sections of the Toolbox are also provided below.
The tools used for managing cormorant/fishery conflicts have been grouped based on the underlying issue being addressed – for example, reducing the availability of the fish to the birds. For each group, the linked text highlights the main advantages and constraints surrounding the use of available tools and provides a general evaluation in terms of their efficacy, practicability, cost and acceptability.
1. Scaring cormorants away from a fishery
The basic philosophy behind techniques to scare birds away from a fishery is that cormorants are startled sufficiently to move to other foraging sites by means of auditory, visual or even chemical deterrents. Clearly, the effectiveness of these techniques relies on: (i) the deterrents being sufficiently frightening to cormorants to make them move elsewhere, and (ii) there being a ‘better’ alternative site to which they can move.
The main drawback of these techniques is that cormorants eventually (often quite quickly) realise that they offer no real threat and the birds become ‘habituated’ to the noises, sights or smells, ignoring them thereafter. The key to the successful use of auditory and/or visual deterrents seems to be to make them as unpredictable as possible by changing their location and frequency of use, and by using a number of techniques in combination.
There is also good evidence that birds are scared consistently by human presence if they perceive that humans are associated with danger. Where this is not the case, the birds can sometimes be approached at close quarters and show no apparent fear of man. This might explain why the scaring effect of non-lethal measures can be intensified when combined with shooting some of the birds – action that requires obvious human presence. If deterrents are used in conjunction with highly-visible human presence, this will increase their overall efficacy, but it may also increase their overall cost. As with many other techniques, it seems best to operate deterrents before or as soon as birds arrive at a site – thus preventing them from getting used to the area as a foraging site in the first place. Once birds have learned that a site is good for foraging or breeding, it will be much harder to deter them from visiting it.
Details of the range of tools within this category are available here.
2. Protecting the fish – exclusion techniques
These tools involve excluding the birds from the fish. Not surprisingly, the techniques work best when fish are concentrated in relatively small areas. Thus, they are ideal for land-based ponds or raceway fish farms where netting enclosures can be fixed permanently. At other sites, such as fish farm cages in open bodies of water, anti-predator netting can be hung in ‘curtains’ or as complete enclosures underwater to prevent diving birds reaching fish stock in the mesh ‘bag’ of the cage. In larger water bodies, complete exclusion is far more difficult and may well be impractical. At such sites it may be possible to take advantage of the fact that cormorants generally require quite long distances for take-off and landing. By positioning wires, ropes or mesh barriers across waters it may be possible to make it difficult, or impossible, for cormorants to land on, or take off from, the water’s surface. Although certain deployment arrangements (e.g. spacing of wires) appear to be more effective than others, there is considerable scope for experimentation at fishery sites.
Details on exclusion techniques are available here.
3. Reducing fish availability to cormorants – fish stock management techniques
The idea behind this selection of tools relies on the fact that cormorants, like all predators, need to make a number of choices when selecting where to feed. They have to balance a number of issues if they are to obtain their daily food requirements. These will include the body state of the bird (whether it is losing or gaining weight), environmental conditions (more food/energy is required during colder/wetter periods), the state of the annual cycle (migration periods, breeding season, over-wintering), the brood size and its age, and the distances between roosts or colonies and feeding sites. Foraging site choice is also dependent on the ‘availability’ of suitable areas and both the number of potential feeding sites and their ‘quality’. In simple terms, ‘high-quality’ foraging sites will be those that offer risk-free, undisturbed access and feeding, with good supplies of relatively easy-to-catch fish.
While many techniques involve the deterrence or exclusion of cormorants, there are also a number of ways in which cormorant-fishery conflicts might be influenced through the management of the fish stocks themselves. Such techniques attempt to alter the ‘quality’ of the foraging opportunities available to cormorants by trying to make fish less easy for the birds to catch. The underlying principle is that if fish are difficult to catch, then the birds may choose to feed on other waters where the fishing is easier. For example, where fishery managers have control over fish stocking regimes, there are several options that might reduce fish losses and make sites less attractive to foraging cormorants.
Details on various fish stock management techniques are available here.
4. Reducing fish availability to cormorants – habitat modification techniques
The philosophy behind this set of tools is an extension of that described previously in relation to fish stock management. These tools aim to make sites less attractive to cormorants for roosting, nesting or feeding. Such tools will never stop cormorants from roosting, breeding or feeding altogether but, at a site-specific level, they may reduce or eliminate cormorant presence in an area and prevent birds ‘colonising’. They may also help to make foraging sites less attractive to birds thus encouraging them to move elsewhere.
If there are no other safe roosting sites for some distance, cutting down a few trees on the banks of a pond may be enough to make a site unattractive for birds. Preventing the establishment of a cormorant roost site may stop cormorants being attracted to an area by the presence of other birds, or may prevent subsequent attempts at breeding - roosts are often the precursors of colonies. Providing additional cover for fish (e.g. refuges) can reduce their availability to cormorants and make sites less attractive as potential feeding sites. As with most, if not all, of the available techniques, their use will be most effective if applied with a good knowledge of the region and the behaviour, movements and daily foraging patterns of cormorants in the area.
The options for reducing cormorant-fishery conflicts by altering the habitat both above the water and below are available here.
5. Reducing cormorant numbers
Practical experiences indicate that most non-lethal defence measures are more effective on smaller bodies of still and running water; they may be less effective or even impractical on larger stillwaters and rivers. Against, this background it is not surprising that those affected by cormorants often see shooting, or other lethal measures, as the more effective strategy for protecting their fisheries, particularly where conflicts occur over large areas. However, in practice there can be similar problems with this strategy as with non-lethal scaring methods, since dead birds can very often quickly be replaced by others. This is particularly true at sites, or broader areas even up to national scale, on cormorant migration routes in autumn and winter, but may also be the case at other times of year if cormorants are moving freely between locations.
Further details on the use of lethal measures to reduce cormorant numbers at different geographic scales are available here. A more detailed consideration of the issues related to potential management of cormorant populations on a pan-European scale is available here.
The extent to which different actions have been taken to reduce cormorant numbers across Europe was collated on a country by country basis as part of the INTERCAFE COST Action. A summary of this information is available here in INTERCAFE ‘Cormorants and Environment’ report].
6. Financial compensation
Many national authorities take the view that the cost of managing cormorant conflicts should be borne by the affected stakeholders. Thus, financial compensation arrangements are generally considered inappropriate. However, financial compensation is used in some countries to offset the consequences of cormorant predation for particular stakeholder groups. Such measures are largely, but not exclusively, restricted to fish farms and hatcheries, with losses of fish consumed and damaged by cormorants being covered (though not always fully) by compensatory payments.
Further details on compensation are available here.
Cormorant management techniques can be applied over very different temporal and spatial scales. At one extreme there are very localised, short-term, site-specific measures and, at the other, the potential for long-term population control measures at the pan-European level. In practice, management quite often applies at scales intermediate to these, with programmes being established, agreed and co-ordinated over a wider, but still relatively local, area.
Further details on a range of different management case studies are available here. These help illustrate the use of cormorant management techniques at different scales and highlight some of the complexities and difficulties that can affect management programmes. The examples range from relatively small scale, site-specific cases and targeted trials to larger, programmes co-ordinated over wider areas and national management plans.
Additional examples of stakeholder concerns and experiences relating to cormorant/fishery conflicts, some of which include information on management approaches, are planned to be made available through this Platform in the near future.