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Fisheries Management Fish Refuges Refuge Development
Research and DevelopmentUnderwater habitat plays a key part in the interaction between fish predators and their prey. Weed cover and other submerged structures are widely used by prey fish to reduce the risk of predation from pike and other predators.Research has shown that the survival of prey species increases and the growth of predators such as pike decreases, as vegetation density become greater. The extent to which this might apply to cormorant/fish interactions is less well established, but there is every reason to believe that similar factors apply. Cormorant numbers on inland waters vary over the year as birds move between breeding and over wintering areas, but are highest during the winter period. Unfortunately, this is when the natural cover available to fish is at its lowest level because aquatic weed dies back. In addition, fish swimming speeds are governed in part by water temperature and hence are also at their lowest level during this period. Therefore, cormorants can often swim faster than most of their prey species at this time of year. Other anti-cormorant measures  The use of nets or wires can also exclude or deter fish eating birds such as cormorants from accessing a particular site and, owing to their durability can provide a long term option for reducing the risk of predation. Net enclosures can completely enclose a site and excludes all birds, in contrast ‘wires’ can deter birds but are unlikely to exclude them altogether. Nonetheless wires can still be effective at reducing the losses of fish and are particularly effective where the birds have access to other feeding sites.Nets and wires are viable management options at reducing predation loss at some sites can but be costly, however temporary structures can be put in place to reduce this cost, this is most applicable in winter months where fish are more susceptible to predation. Nets and wires should be regarded as one of several tools for managing cormorant/fishery conflicts. The durability and potential long term efficacy of these techniques should be weighed against the losses to predation and the cost of alternative deterrent measures in assessing the applicability to any site. The A.G.A Group are happy to offer advice on such matters and can often present sustainable solutions to combat predation loss without resorting to lethal methods. The graph shows the relative effectiveness of the different deterrent categories (Bishop et al, 2003). Habitat modification, lethal techniques and exclusion appear to be more consistently effective than auditory, visual or chemical techniques. However, the number of studies investigating habitat modification and exclusion, in particular, are extremely small (one and five respectively). For more information on any of the A.G.A Fish Refuge products, why not call one of our trained advisors on:
Telephone: +44 (0)1953 886824 Email: This e-mail address is being protected from spambots, you need JavaScript enabled to view it |
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| Last Updated ( Thursday, 24 April 2008 12:31 ) |
