Killing predators is not the only way, explains Stuart Manwaring

It is estimated that there are over 24,000 over-wintering cormorants in England. Over 14,000 of them come inland. Why do they come inland though? A cormorant can happily take between 0.5 and 1kg of fish per day to sustain itself.

Our waning sea fisheries have been a cause for concern for many years and perhaps times are tough for cormorants out on the coast. Head inland though and you will find a proliferation of freshwater lakes and rivers.

I am a fisheries officer employed by the Environment Agency in Wallingford. One of the best parts of the job is working with angling clubs to help improve their fisheries. The work I do is funded directly from rod licence sales and it’s always good to give something tangible back.

A local organisation, Sutton Courtenay Angling Club, noticed a decline in catches at their Phil’s Lake venue in Abingdon and this was attributed to cormorant predation as they had noticed a number of the birds visiting the lake on a daily basis. The ramifications of this are obvious. A fishless lake is no good for a fishery owner who may be reliant on income from anglers as an important part of his or her livelihood.

From a very quick Internet search I was able to discover that the most likely collective noun for a group of cormorants was a ‘gulp’. Having watched the way they consume their catch this would appear an appropriate name.

Ask almost any angler though and the term ‘plague’ will be used. The dictionary has several entries under the heading ‘plague’. These range from the bubonic to the biblical and are generally associated with an increase in numbers of a destructive or unwanted animal.

The site of 10, 20 or even 30 black shapes, roosting with malicious intent, on the dying branches of alder trees all year round, is now a common sight. Our native fish populations, forever in a delicate balance with the natural bird predators many of us love to see; the heron and the kingfisher for example, have taken quite a hit from these novel predators. Add to this man’s misuse of our river catchments, and it’s no wonder that, in places, fish populations are struggling.

So what options then for the beleaguered angling club committee or fishery owner?

The knee-jerk reaction can be to stock with more fish. However, to annually replace those lost to predation can quickly become costly. We’re talking thousands of pounds here.

The more extreme voices out there will be calling for a cull of these birds. I recognise the problem but any time the word cull is mentioned it stimulates strong emotions.

How often is the call for a species to be culled because it appears into a niche that is inconvenient for it to occupy or indeed it occupies far too well? Of debatable value and questionable morals is the control of cormorants through the employment of firearms. Although protected by legislation a licence can be granted to shoot a limited number of cormorants per year, provided strict criteria have been met.

More commonly, fisheries are resorting to less destructive methods to counter the threat of predation. Unlike herons and kingfishers, which tend to wade in shallow water or plunge from a perch, cormorants will swim in open water and actively chase their prey.

Trials involving sunken reefs proved that where refuge was available to fish the success of each cormorant hunting foray declined and the time they took to catch a fish increased. Eventually the birds stopped visiting the study pond.

A control pond with no refuges was pretty much devoid of fish when it was drained down after the study, whereas the pond with refuges in it still contained fish. There is no official specification for these underwater reefs. Anything that can be submerged and provide some structure has worked.

With the help of the Sutton Courtenay Angling Club we, therefore, constructed a set of fish refuges. These were made with rolls of stock fencing floated under waste pipes designed to provide a safe haven for fish within the lake and give them somewhere to hide from the cormorants.

The refuges are non-destructive for the cormorants, but the fish will now hopefully be able to grow to a size that’s cormorant-proof (once they get to a certain size, they are too big for cormorants to eat).

As a helping hand to the club we also stocked in several thousand fish to help them along. It should work. Whether the fish are clever enough to work out the refuges remains to be seen, but the cormorants have been seen diving around the edges which tells me that the fish are hiding, so I think the refuges are doing their job.

The tench and bream we stocked should be cormorant proof within three to four years, so it is a long-term project, but in the meantime we hope it’s a way of keeping everyone happy.

Stuart Manwaring is a fisheries officer with the Environment Agency, based at Wallingford