Anglers and cormorants

Spend a little time out fishing, no matter where, lake or river, talking to other anglers, and soon enough the topic of cormorants will arise. Nearly always the view is the fishing was so much better a few years ago before the cormorants began eating all the fish. I’ve heard this said on numerous occasions, even on waters that have plenty of fish. Exaggeration is commonplace too. The claims of mighty catches a vague number of years ago is rarely plausible, especially when such boasts have been around well before cormorants were deemed to be a problem. The question also arises of whether fish declines, assuming they are occurring, are caused by cormorants or some of the many other factors we know affect the freshwater environment.

The cormorant that has appeared around many of UK waters over the last 30 years is the continental sinensis subspecies. This is not the same bird as that found around our coasts and the rise in its numbers has nothing to do with marine fish stocks. Cormorants in Europe were heavily persecuted up to the 1970s. Now they are protected the population has increased substantially and birds have migrated to the UK. Lobbying in Europe gained permission for selective control where it could be shown that fishery damage is occurring and where other control methods don’t work.

Now the Angling Trust has released a paper calling for cormorants to go on a general shooting licence, giving clubs and fishery owners the right to kill birds at will. The paper goes in for some hyperbole: ‘a massive and unsustainable increase in cormorant numbers…’, ‘decimated by cormorant predation’, etc. Perhaps unwisely it cites the Avon Roach Project, claiming an EA stock survey in 2005 showed roach stocks to be ‘perilously low’. In fact the EA data show nothing of the sort. Unless there is other data not included in this otherwise comprehensive set, the claim is exaggerated at best. Further, the person who started the ARP, refers to the cormorants as ‘not even British’. Not a good choice of words in today’s xenophobic climate.

The AT cites a number of academic research papers in support of its case. Notably very few concern research in this country. The majority are on work done in Denmark and other European countries, and one in Japan. Out of 26 references, only two are both in peer-reviewed journals and describe studies carried out in Britain. I wonder whether the authors of the AT paper have actually read these.

The Danish publications in particular do find that cormorants consume a significant quantity of fish. Others are ambivalent; some find that fish are not greatly impacted by cormorants, some find only certain species are affected. A general observation is that it depends on the kind of water and the local geography.

I’ve taken a look through the journal research papers published on the topic of fish predation and cormorants. Most are not available to the general public, unfortunately, although they are technical papers and not digestible reading. I found that surprisingly little research has been conducted on UK fisheries, and much of that is 20 years old or more. One useful review article by Catriona Harris et al in 2008 considers the impact of piscivorous birds in Scotland. The conclusion is important:

‘In summary, there have been few quantitative studies undertaken that have actually demonstrated reductions in [fish] population size or productivity as a result of cormorant predation in Scotland’

Stewart (2005), cited by Harris and also the AT, examined the effect of cormorants on Loch Leven. This amply demonstrates the difficulty with these studies. The area of water is so great that only rough estimates of fish population can be made, and these are very uncertain. Similarly the total number of fish taken by cormorants is also an estimate with large uncertainty. This leads to some perverse results in which upper estimates of predation exceed the fish population. It is still a viable fishery so we know not all the trout have gone. Quantifying impacts on fisheries is clearly extremely difficult.

Cormorant impact on natural waters is either uncertain or thought to be slight. But it may well be a different matter on waters which are created specifically for fisheries and are densely stocked. Ian Russell at Cefas in 2008 conducted an experimental study on fish refuges, comparing predation on two neighbouring experimental ponds, one with refuge cages. The control pond (without refuges) was heavily predated, removing the majority of stock, whereas the pond with refuges only lost around half. This shows, given the right conditions, cormorants will scoff with abandon. But one should take into account the artificiality of the arrangement, a control pond with no weed or debris, also clear and shallow — an ideal fish restaurant from the cormorants’ point of view. In an earlier paper, Kirby et al noted:

‘Indeed, the current diet of the cormorant appears to have been strongly influenced by man, who has altered the natural balance of fish stocks in many situations (e.g. trout stocking) and perceived problems are more frequent in such artificial situations.’

Overall there is little evidence to suggest cormorants are having an adverse impact on natural populations of fish, but some does point to problems with cormorants in artificial waters. The question is what to do in the latter cases. Anglers clamour to shoot them, but here the evidence for the effectiveness of culling is lacking. Rather than reducing bird populations, Chamberlain et al found that shooting caused them to grow. Cormorants killed are just replaced by others from the mobile population. They are opportunists and will fill any food-ready vacancy. The only way cormorant numbers could be reduced would be a return to persecution throughout the UK and Europe. And that isn’t going to happen.

So how will the AT’s representation and that of all other anglers to DEFRA be received? Given the lack of evidence of cormorant damage on the scale many anglers believe, and the evidence that shooting does nothing to reduce numbers, it is most unlikely that a general control licence will be granted. Cormorants, like otters, will have to be accommodated. That means adapting fisheries to minimise their impact. Wildlife experts say that cormorants, and all birds, need somewhere safe to rest between fishing dives. The further away from the water, the less likely the birds will choose that source of food. Dead trees are a cormorant favourite, as are islands or man-made objects in the water. Reducing these may reduce the cormorants. Natural weed growth, woody debris all help the fish avoid becoming a meal. And above all, lower fish densities make life harder for the birds.

The INTERCAFE project seeks to bring interested parties — anglers, fishery owners, scientists — together so that some resolution to the conflict between cormorants and fisheries might be found. This is probably the best way, perhaps the only way forward. We are going to have to live with cormorants.

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