Piscivorous wildlife is often perceived as competitors by humans. Developing management strategies that account for avian predator response to variation in the prey fish community will be important for increasing the survival of threatened and endangered salmonids in a changing environment. This work shows the importance of understanding the broader food web. These results demonstrate how temporal variation in one prey type (marine forage fish that enter the estuary later in summer) can indirectly reduce consumption of another prey type (juvenile salmonids) by a common predator (piscivorous birds)-an apparent mutualism. In contrast, cormorants showed a weak, linear response in this relationship. Caspian terns responded nonlinearly to the availability of marine forage fish, with the proportion of juvenile salmonids in their diet significantly declining when the proportion of marine prey species available exceeded a threshold of 48%. However, consistent seasonal differences were observed in the mass of salmonid and marine forage fish prey in net sampling and the diets of piscivorous birds Caspian terns had a higher proportion of salmonids in their diets than did cormorants or net sampling across seasons in all years. The composition of Caspian tern (CATE) and double-crested cormorant (DCCO) diets broadly overlapped with each other and with independent purse seine sampling.
The diet of two piscivorous bird species nesting in the lower Columbia River was compared with purse seine samples of the fish community to explore the influence of alternative prey availability on the consumption of juvenile salmonids in the Columbia River Estuary. Here, demonstration projects could involve a reframing exercise, coupled with new scientific research and practical experimentation within an adaptive management framework – one aim of which might be to increase the scope and geographical coverage of effective management activities. It also proposes that future research might best focus on specific fisheries sectors that appear to be ‘hotspots’ for conflicts. As such, this paper draws on a ‘reframing’ model proposed to deal with such situations and discusses the various ‘frames’ by which issues are viewed.
Much of the controversy over Cormorants is fuelled by differences of opinion and, coupled with its persistence and entrenched nature, it has many of the characteristics of a so-called ‘intractable environmental conflict’. Using case examples and experiences from several pan-European studies and research networks, this paper describes the complexity of this issue and the diversity of associated opinions.
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The central European policy issue is thus how to deal with: (1) a large pan-European population of Cormorants, (2) very often breeding in some Member States but overwintering and preying upon fish in others, (3) where there is generally a lack of unequivocal scientific evidence for predation impact on fisheries and (4) where there are growing political calls for coordinated European management, whilst (5) many believe that the site-specific local/regional management advocated by some is ineffective.
Consequently, Cormorants have increasingly come into conflict with fisheries interests across Europe, as many people believe that the birds are now so numerous that they cause declines in fish catches, with associated impacts on commercial and recreational fisheries. sinensis) comprises over 80% of the European breeding population and its numbers and geographical distribution have increased and expanded dramatically in recent decades. One of the most widespread and persistent environmental conflicts in Europe involves the Great Cormorant (Phalacrocorax carbo).
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