The Fish Rescue
|The United Kingdom has a fairly extensive canal
network with lengths from Exeter, Devon to Edinburgh in Scotland. Through
the mid 19 hundreds the canals became rather disused; this was due to commercial
goods transport moving to the road and rail networks. However, over the
past 10 years the canal has returned into the limelight with huge grants
allowing essential maintenance; this is especially the case on the Kennet
& Avon canal in Devizes and the Union Canal in Falkirk. This increased interest,
and some may suggest trend, in living by waterways has encouraged the canal
owners, British Waterways, to continue with essential work to maintain the
|So with all of this work underway how and why do fishery consultants become involved? The canals have always been a favourite haunt for anglers; this has resulted in thousands of pounds of fish being stocked over the past fifteen years. On many occasions the scheduled work requires the removal of the water. The replacement of lock gates, repairs to culverts, lining of canal beds, dredging and piling are common practice, but before these essential works can commence the canal section requires de-watering.|
|These three images show why water is removed from canal sections. The
picture on the left was taken at Farmers Bridge, Birmingham on the Birmingham
& Fazeley Canal where extensive re-development work is on going. A series
of lock pounds were drained to allow bank side renovation to take place;
the aim is to rejuvenate the area with new housing and office buildings.
Of the twelve pounds along the Farmers bridge length all but one drained
to an efficient narrow section on the towpath side.
The image in the centre shows recent lock gate renovation work at Cosgrove on the Grand Union Canal Main Line near Northampton. The removal of lock gates will always lead to de-watering. However, as many locks have a bridge situated close by the use of stop planks can be employed hence leaving short drained sections.
On occasions a further problem is uncovered once the section has been de-watered. At Cosgrove (image on right) a hole was located in the bank, but luckily four grade 1 British Waterways staff were on hand and were left to look into it!!!
|There are various ways to de-water a section of canal. Two solid barriers are required; therefore, short pounds with adjoining locks are ideal. Unfortunately this scenario is rare so other water retaining methods need to be employed. Stop planks can be placed in the purpose cut grooves located underneath bridges.|
|When the use of stop planks and lock gates as dams is not possible temporary structures are required to hold vast quantities of water back. The common choice is the use of an impervious fabric membrane attached to a free standing steel support system. These 'Portadams' are fixed across the canal, shown in the above pictures (Horton Bridge, Kennet & Avon Canal), and then with a slow drain down the sheet is allowed to seal creating a water tight barrier. This system allows work to be undertaken on otherwise non-accessible sections. However, they have a tendency to breech, especially in the siltier sections, so jobs are commonly held up while complete sealing takes place.|
|These two images show the completed dams in place. On the left is the dam at Horton on the K&A Canal; note the drag net can be seen still in place behind the now completed dam. On the right is the fitted dam at sheepcote street, Birmingham. This was a larger dam thus did experience many problems before a seal was achieved.|
The ideal conditions for a successful fish rescue consist of a width near to 4 metres and a depth 0.45 metres. However, these conditions are rare due to the varied contours found on the many different sections of canal. Silt deposit levels and recent dredging exploits also influence depths. Whatever the conditions presented the rescue needs to be completed, therefore methods vary to suit each job.
The concept is simple. A small boat is pulled along the canal section behind 3 - 4 electrofishermen. The boat contains a generator linked to a control box. From this box run two hand held anodes and one cathode; this is connected to the rear of the boat. 240 volts and 6 amperes are generated and a direct current is implemented. The current is applied via the use of two "dead man's switches", one on each anode. Also within the boat there can be up to four large bins of water which hold the captured fish.; each bin has an aerator pipe that is connected to a battery powered air pump. Up to three stop nets of various sizes can also be carried. Each bin can hold up to 100lbs of large fish or 50lbs of small before they need to be emptied.
With a three man team the outside men will control the anodes, sweeping left to right, whilst the centre man controls the boat. Each team member will also use a small net to collect stunned fish. Large nets are held in the boat if substantial amounts of fish are encountered. If a forth team member is utilized the man can be placed in one of two positions. If the presented canal still has a wide area of water the forth man would be suited at the front alongside his team members. However, if conditions are either 1) good (narrow); he can follow behind netting the smaller fish that rise late (usually perch & ruffe), or 2) Very silty; he will probably have to push the boat if the substrate offers difficult walking conditions.
The length of the canal section is the usual determining factor that dictates where the job will commence. It is beneficial to work into clear water, therefore, if groundwater is entering on the length then the electrofishing should always take place towards the source. However, if the section is being pumped or drained whilst the rescue is in progress then working away from the running pumps or open paddles is again preferable. Incidentally, it is not always possible to fish into clear water as accesses are not always available to launch the boat from.
Once a suitable area has been found for launching, and the water flows and colour has been assessed, the work can commence. The process is fairly simple, however, there is one hard and fast rule. No matter what conditions are presented the job is not complete until all of the fish have been removed. This could mean up to four runs of the whole length; usually two complete runs are sufficient to remove the fish.
|These three pictures show a successful fish rescue in progress at Yelvertoft on the Leicester Line of the Grand Union Canal. These conditions are almost perfect offering a narrow canal and constant depth. The silt levels through the boat channel are low which allows easy walking conditions. Unfortunately I needed to leave the water to take these pictures, however, with the offered conditions I would have been seen approximately 20 metres behind the boat collecting the smaller ruffe and perch that show late. The electrofishermen can be seen on each side with a hand held anode and an accompanying netsman in the centre. The picture on the right gives a good indication of the parallel line kept by the probe users. If one were to fall behind, this coinciding with large numbers of fish, then the fish shoal will tend to charge the withdrawn side. If kept level the fish are moved slowly up the canal until they meet a solid barrier; a net can be dropped behind at this point trapping the fish into a short section. The creation of a diagonal current caused by a withdrawn anode will cause increasing problems as a section becomes wider. The section above is sufficiently narrow so not to be effected by sloppy working practices.|
|The picture on the right gives a clear view of the contents inside the electrofishing boat. The electric box can be seen on the front of the boat (grey) with the yellow cables of each anode attached via specialised waterproof four pin plugs; the UK standard colour for these plugs is blue/grey. The box is connected to the generator (red) which is situated in the rear of the boat. The generator can usually be found in the rear as it counteracts the water bins (yellow) in the front. To the left of the generator the air pump can been seen; the pipes and diffusers from this pump run to the water bins. There can be up to five bins in the boat at any given time. The picture on the left shows an electrofisherman working an anode whilst netting small roach. He can be seen in a full dry suit and gloves, the only realistic clothing to carry out fish rescues in.|
|These two pictures show the working conditions in and around solid structures. The image on the left shows a simple lock system that requires navigating before the next section can be fished. Note the large amount of ice in the lock; never assume all jobs are warm and fun!! The second image gives an excellent view when approaching a portadam.|
|On occasions it is possible to carry out a drag down with a net before
a dam is put in place. These pictures, taken at Horton Bridge, near Devizes
on the Kennet & Avon Canal, show the aforementioned drag down in progress.
This method has shown to be very effective in herding shoals of bream and
large roach from the target section. Years of scientific testing, with regards
to the effect of electrofishing on certain species, has continuously revealed
potential damage to fish when exposed to long bursts of electrical current.
Therefore, any opportunity to remove fish from the section with methods
other than electricity will always be employed.
A canal drag-down is usually undertaken with a small seine net rarely exceeding 25 metres in length. Again the concept is simple. The net needs to be a sufficient depth to cope with the drag-down; therefore, a net exceeding 1 metre at the deepest point of the canal is required. A man works each bank from the water by pulling the net towards the dam frame; it is imperative that the net stays of equal distance between workmen. The middle of the net needs to be in the centre of the canal. The images above show the net being pulled towards the dam frame (left) and of the excess net bulging behind as the net is pulled (centre). Incidentally, this method is not always feasible as dragging nets is both time consuming and energy sapping. In reality very long stretches cannot be netted as the efficiency decreases over long lengths due to snags.
As a net is pulled through a section numerous obstacles will be encountered. Many areas of canal are used as dumping grounds for all types of rubbish; this will affect the efficiency of any drag-down. As these snags are uncovered the leads attached to the base of the net need careful manoeuvring over the obstacle. The worst type of snags include bicycles, tree branches and brambles and the mandatory car engine. However, if the canal is not to deep most problems can be solved. This image (right) shows a large branch being removed from the net.
|These two images taken at Sheepcote Street, Birmingham on the Birmingham & Worcester Canal, show a relatively inefficient electrofishing exercise. The catch efficiency of a canal section drained to this width would be less than 50%, however circumstances sometimes dictate that rescues need to go ahead. This section had prolonged problems with holding water back, but the section was finally drained and a successful rescue was completed.|
|Occasionally some very difficult conditions are put in front of a rescue procedure. As many rescues are linked with hugely expensive civil engineering projects the time scale available is always short. Therefore, problems other than deep water, which cannot be solved, require tackling and over coming. These two images were taken in January 2002 at Yelvertoft on the Grand Union canal Leicester Line. This stretch was approximately 2200 metres in length and when presented had 2 inches of ice across the surface. For obvious reasons a rescue could not be undertaken, the only solution was to launch the boat, find some heavy poles, and then tow the boat whilst breaking the ice.|
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