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It’s time for fishery owners to spring into action!

Fisheries management tips on preparing your fishery for spring by Dr Bruno Broughton – Fisheries Management Consultant

In the next few weeks we will all see welcome tell-tale signs that spring is arriving. Willows will develop catkins; primroses will appear as if from nowhere; pairs of great-crested grebes will perform that fascinating mating dance; mute swans will begin collecting dead reeds and rushes with which to construct their nests; and fish will be on the move again after their winter torpor.

You could be forgiven for imagining that now is the opportunity to simply sit back and enjoy the sights and sounds of spring. However, it’s actually a busy time when you should be attending to a multitude of tasks in and around your fishery… to repair winter damage, to protect fish at a crucial time of year and to undertake vital management tasks. This work will pay dividends come the warm and hopefully the not too hot summer ahead.

Prepare To Repair

Winter storms, heavy snowfall, freeze-ups and flooding all contribute to the damage inflicted on fisheries. Fallen trees and large tree branches should be removed if they are obstructing paths or pegs; smaller trees which fall into lake margins between pegs can be left in place, if appropriate, to create additional habitat for aquatic invertebrates, the food of most fish. Underwater branches also create areas of cover for fish and refuges to help avoid predators.

Trees which have become dangerous to anglers should be pruned or even felled completely for sensible health and safety reasons. This is also the justification for allowing only qualified, experienced people to undertake any significant work, even if that means employing professionals.

However, any arboricultural work of this nature must by law avoid damage to nesting birds, their eggs and their offspring. Most birds nest between the beginning of March and the end of July… but some will do so outside of this period. It is best to inspect any trees or bushes that are to be cut to ensure that active nests are not present.

Damage to the surfaces of paths and pegs should be put right, whilst crushed bark or similar peg infill material may have to be replenished. Particular attention should be paid to platform pegs which protrude over water to ensure that they are safe and in good repair. Surface boards may need to be scrubbed to remove accumulated bird droppings, algae, leaf litter and similar debris that can make them dangerously slippery when wet. Stapling wire or plastic mesh to the boards greatly reduces the risk of someone ‘taking a flier’ into the wet!

Erosion of lake banks is likely to be most noticeable as winter ends and repair work should be enacted to make good the damage. (This topic was covered in my last article, ‘Winter Protection Work’.)

The result of two hours raking Canadian Pondweed from the margins at one peg on a fishery The result of two hours raking Canadian Pondweed from the margins at one peg on a fishery

Happy Fish – Happy Anglers

It’s sometimes said that if you look after the fish, good angling will be assured. Nothing is ever as simple as that, although there is a core of truth because the converse is certainly the case: unhappy – read ‘underfed, disease-ridden and damaged – fish usually result in poor angling and unhappy anglers – and bad news spreads like wildfire amongst the local angling community.

First and foremost, fish need access to good spawning habitat, be it beds of soft, submerged water plants, marginal vegetation growing out into open water, the fine white, feathery, underwater rootlets of bankside willow trees and bushes or tree and bush branches that hang into the water. The fertilised eggs will stay attached to the spawning substrate until they hatch, and the new fry will stay in place in the cover until they have used up their yolk sacs and need to venture out for new food.

A well-run fishery will often already have suitable spawning sites, but some lakes may lack such features. Here, intervention by providing ‘spawning mats’ known as kakabans is an appropriate management action that can be undertaken easily and at very little or no cost.

The simplest kakabans are merely faggots formed by lashing together bundles of tree branches and then installing them in the shallow edges. Branches cut from Leylandii trees or hedges are particularly good because the leaves are fine, soft and long-lasting. They will probably need to be anchored in position, for example with a short length of rope attached to one or more bricks, to hold them in place. Alternatively, two ropes could be tied to each faggot so that, when the bundle is placed just offshore in a corner of the fishery, each rope can be tied to a stake on opposite sides of the corner.

Somewhat more sophisticated kakabans can be formed using a sheet of fine, greenhouse-shading material cut into long strips a couple of inches wide. One end of each strip is then trapped between a pair of stout wooden slats which are then nailed, screwed or glued together. Done correctly, the mesh strips should hang vertically in the water, like a divided curtain – mimicking a weedbed – beneath the floating wooden ‘sandwich’.

Obviously, fishing should be prohibited in any area where spawning devices have been installed until it is obvious that spawning has ceased, the eggs have hatched and the fry are now free-swimming. The kakabans can then be removed.

There are plenty of spawning opportunities for fish in this lake There are plenty of spawning opportunities for fish in this lake

No More Cuts

Such is the enthusiasm and vigour with which fish spawn that they can inflect nasty wounds on themselves while ‘getting their fins over’ including loss of scales, split fins and cuts to their flanks. This is especially the case where there is little soft spawning habitat and fish attempt to lay eggs in the hard bottom substrate.

Flooded, former sand and gravel quarries such as those in East Anglia contain far more sharp flints that those elsewhere. I found that carp attempting to spawn in several such fisheries were slashing their bellies and flanks on these flints. Here, the solution at each lake was to create a U-shaped channel several yards wide, with the open ends connected to the main lake to enable carp to access the channel. Sand still present at each site was then spread over the channel bed, ‘blinding over’ the flints. The channel was then planted with lots of rushes.

On each occasion the channel became extremely popular with carp come spawning time and damage to their bodies ceased. However, because the channel represented a safe area in which anglers could not fish, carp would hang around there well outside spawning time!

Infection Detection

Spring is also the time when many fish pathogens become active. They include:-

  • Fish lice – small, disc-shaped parasites, each with a prominent pair of dot-like eyes, which attach to the bodies and fins of fish. Severe infections can lead to secondary infections through the pin-prick wounds.
  • Leeches – small dark or black worms attached to various parts of the fish body by one of the end suckers. Again, it is only heavy infestations which lead to serious problems.
  • Small skin parasites – although invisible to the naked eye, heavy infestations by a variety of skin parasites can impair fish health and lead to death. Reddening of the skin, fin damage and excessive mucus are common symptoms.
  • Bacterial infections – of which there are many. External symptoms usually include body wounds, including fin rot, sores, ulcers and lesions.
  • Viral diseases – including Koi Herpes Virus (KHV). Viruses are serious fish killers and although sores and other body damage may occur, infected fish may not show any external symptoms.

The mere presence of a few external skin parasites or small body wounds is quite natural and should not be a cause for alarm. However, if fish show signs of significant infection, or if they begin to die, the Environment Agency should be contacted immediately.

The 24-hour ‘freephone’ emergency ‘phone number is 0800 807060 and is printed on every rod licence.

The fruits of successful carp spawning The fruits of successful carp spawning

Curbing Veggie Gluts

In one form or another, water plants are present in every fishery, even if – as with some suspended algae – they are each barely visible to the naked eye. Indeed, the natural food of fish either includes aquatic plants or relies of them for nutrition, hence the complex food webs that exist underwater.

However, over-population by plant life can jeopardise fish health and survival, particularly because of oxygen depletion after dark during hot weather. It can also make angling problematic, or even virtually impossible, where huge weedbeds are growing over an entire fishery.

Several means of intervention can be employed to control the proliferation of submerged water plants and the development of dense algal blooms. It is preferable to act before the weedbeds become too dense and the blooms really intensify as there are fewer plants to control. Weighted weed rakes attached to strong ropes can be deployed at small fisheries to create fishable swims. The longevity of such control measures is extended if the cleared areas are ‘over-raked’ so that any fine plant roots are also removed. This works very effectively with Canadian Pondweed. On larger water bodies, raking is obviously impractical.

Dye Hard

One relatively recent innovation entails the introduction of harmless water dyes which help to ‘shade out’ submerged plants. Although the dyes are available in a variety of colours and are aimed at both ornamental pools and recreational fisheries, their modus operandi is to reduce the penetration of infra-red light – essential for submerged plant growth – rather than all light wavelengths.

Water dyes are sold in an assortment of colours and are suitable for several aquatic situations including ornamental ponds, fish farms and recreational fisheries. Research has demonstrated that the dyes are non-toxic to fish and other water organisms; they do not bio-accumulate; they do not pollute water either directly or because of any residues. The Environment Agency has confirmed that their use does not require its consent.

Because the dye gradually loses its effectiveness with time as it is diluted or becomes absorbed into plants and bottom sediments, repeat applications may be required during the plants’ growing season. The dyes are effective against filamentous algae and submerged water plants providing they are growing in water of sufficient depth to ensure that the shading effect is achieved. For example Dyofix, the main distributor of water dye, recommends that the dye is used in water of at least two feet deep.

In recreational fisheries, where the blue-coloured version may not be aesthetically appropriate, the alternative is to use ‘Dyofix SGP Shadow’ which causes little noticeable change in the water colour but is effective against algal growths. Details of these products and a calculation chart from which the required quantities of the dye can be calculated are available on the manufacturer’s website.

Straw Sausages

There is no herbicide which can be used to treat suspended algae. However, these minute plants can be controlled using barley straw. Although the reasons for the straw’s effectiveness are still the subject of research, it seems likely that the decomposition of the straw causes the release of a complex cocktail of chemicals which inhibit algal growths. These are produced by bacteria and fungi which live on the rotting straw.

It is not possible to provide precise figures on the quantity of straw which should be used in every situation. As a guide, it would be worthwhile using an initial application of between five and 10 normal-sized bales per acre by placing them submerged in the margins. The straw’s effectiveness may be restricted by suspended mud so larger quantities of straw may be required in muddy lakes.

Thereafter, the application rate should be reduced. The second straw treatment can be made with half of the original dose, say two to five bales per acre, and further applications – if required – could be enacted with a maintenance dose of about two bales per acre.

To prevent the bales floating away they should be anchored to the bed or the bank with ropes and bricks, perhaps. Better still to enclose the loose straw in net bags or ‘sausages’, such as the fine plastic-mesh tubes used to pack Christmas trees, and stake these just underwater in the margins. Floats such as plastic, screw-top bottles should be placed in the sausages to keep the straw at or within about three feet of the water surface because the straw is less successful if it becomes waterlogged and sinks to the lake bed.

The sausages should be distributed across the water body, with particular attention paid to areas where current or wave action is greatest as this will help oxygenate the straw and disperse the anti-algal chemicals. In coarse lakes, they can be anchored between pegs or around islands, areas where anglers are unlikely to cause their end tackle to become entangled with the sausages.

The straw is said to work most successfully after it has been immersed in the water for a period. At water temperatures below 10°C it takes many weeks for the straw to become active; at 20°C, the straw will begin to work after one or two weeks. The straw remains effective for between four and six months, after which its activity declines rapidly.

For this reason, straw-filled sausages could be installed during the late winter/early spring in expectation that algal control will be achieved through the spring and summer months. It would be prudent to remove the straw after, say, six months, replacing it with fresh material.

A dense algal bloom on a fishery with poorly-installed straw bales A dense algal bloom on a fishery with poorly-installed straw bales

Further Information

For further information on how to improve the management of your fishery to prevent winter fish kills, reduce siltation, and advice on most fishery-related matters, please don’t hesitate to contact me:

Dr Bruno Broughton B.Sc. (Hons), Ph.D., F.I.F.M., C.Env.
Fisheries Management Consultant

Tel: 01952 691515; Mobile: 07804 651402
Email: bruno.broughton21@gmail.com
Website: www.bruno-broughton.co.uk

Bruno
Written by Bruno Broughton
Dr Bruno Broughton is a fisheries scientist by profession and for a decade worked as a fish biologist and fisheries officer with the former Severn-Trent Water Authority. Bruno has provided advice to more than 1,600 clients throughout the UK – and several in mainland Europe– on a huge range of topics.

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