Saturday, 28 November 2009

Old Birds & Old Fish - Magical museum exibits

Probably your first visit to London was to the Natural History museum. A magnificent building idealistic of the age it was built in with memorising gargoyles' and figurines now staring down on the cueing tourists. A statue of Thomas Huxley greats you as you enter the main doors, the man so in favour of Darwin theories, and so against one of the original museum curators Professor Richard Owen creationist views. As you enter the building the breathtaking high ceilings become engrossing and the architecture just mesmerising and then ….. you head for the dinosaurs!!! 

I love this museum and am unsure how many times I have visited it even though it now seems geared only towards children and foreign tourists. My monthly trip leads me to only four exhibits and it is the same four every time, but to me, they are the only four. Firstly the Mary Anning collection incorporating the plesiosaurs and ichthyosaurs. There is something so very close to home about this collection mostly from the Lyme Regis area. Each fossil has its own story. 

A left turn then takes me to the stuffed replica Dodos. One has to remember no preserved Dodos exist so my ears are covered when hearing a teacher tell his pupils they are real. The story is amazing considering that all stuffed offerings are modelled from drawings; not even a complete skeleton remains. This is a real story of humans’ ability to remove a species in a 35 year period.

From the Dodo I meander pass the children to the memorising display of hummingbirds (Victorian period) pinned to a board. There is something addictive about gazing into this glass case at these beautiful birds until that sick feeling of what you really are looking at hits you. From there I walk straight across the main hall to a small glass tank of formaldehyde sat lonely in an alcove. As I stand there transfixed on a pale white fish people walk to the tank, glance, dismiss, and walk away. Not a second thought is given to the importance of what is in front of them. They throw their eyes at the meaningless tiny plaque that only states ‘coelacanth Latimeria chalumnae Smith, 1939. No body offers more than 10 seconds of their time to study my friend and the museum offers no information as to why they should. At a point in the late 1930s this fish was thought to be the link between wet and dry. The papers were littered with ‘missing link’ headlines. A worldwide hunt started for another specimen leading to an international incident involving France and South Africa. Ultimately the fish was proved not to be the walking miracle once thought but the story behind Marjorie Latimer’s first discovery in 1938 and the events that followed just show how important the scientific world deem these findings. Amazingly it hit the news again in 1998 when a couple of marine biologists on honeymoon in Indonesia spotted one on a wooden trolley in a fish market. This fish was thought only to habit the areas around the Comoros off Eastern Africa. More history was in the making. 

My visits to the Natural History Museum are short and sweet. I hope, however, on your next visit you might take a look at the ichthyosaurs and Dodos, the Hummingbirds and my friend the coelacanth in a new light and for more than 10 seconds.

'The Dinosaur Hunters' Deborah Cadbury ISBN; 1-85702-963-1 
'Dodo from extinction to icon' Errol Fuller ISBN: 0-00-714572-1
'A fish caught in time-The search for the coelcanth' Samantha Weinberg ISBN: 1-85702-907-0

Friday, 27 November 2009

Tuna - The unconsidered alternative

As the wave of opinion gets behind the recent campaign to save the blufin tuna are other key issues being blinkered by this rolling bandwagon? I do not profess to be an expert on the state of tuna fisheries but it is documented well enough to believe that certain stocks of blufin are critically endangered. Any species of endangered animal should be protected and no one could argue against that. The West is the backbone of the recent anti blufin campaign, the very parts of the world that’s insatiable appetite for sashimi has helped to cause such depletions in stock levels. Of course Japan have a lot to answer for but they have, however, been using these species in cuisine for a very long time compared to Europe and the US. So the two problems occur. Firstly what happens to the countries and their fishing fleets that have invested so much money into the infrastructure for catching blufin? The very people encouraged to catch blufin to supply London, Paris and New York? The very people now being blamed for trying to make a living out of an industry the West has turned its back on? The very people that know no other way of life? No wonder the blufin catching countries will not ratify treaties outlawing the capture of their 'own oil'. And secondly, and the most overlooked and crucial point in my opinion, the opinion of a fisheries scientist, is what will happen to the alternative? Well if blufin imports to Japan can be outlawed, the only true way to conserve the species, then a replacement will be required and it will only be the yellow fin Tuna that offers similar tastes and textures. So while we rejoice in saving of the blufin, while we congratulate ourselves on how we forced our hand on many underdeveloped countries and made them change their ways the yellow fin will be shaking its tail in fear. The world is coming to get you – you are the alternative!

Thursday, 26 November 2009

Zander - Coming to a canal, or dinner plate, near you

The other day a customer told me about a fish. He was very pleased that he new about a species we didn’t sell and even spelt it’s name to me. He explained where it was caught, its life history and what it tasted like; the subject had arose as he had eaten it recently in a pub in Kent. Off he went smug in the fact that he had spread his knowledge. The fish in question was a zander (z  a  n  d  e  r) and contrary to popular belief is NOT a cross between a pike and a perch. Just so happened I knew an awful lot about this fish as in the early part of this decade I was involved in an extensive zander culling exercises undertaken on the canal networks of central England. Not since pre ice age was the zander indigenous to the UK. It was re introduced illegally in the 1950s into the Great Ouse and then spread across the linked waterways of the midlands and can now be found as far south as the River Thames. They are a pretty destructive predatorial species that not only seem to hunt in packs but also, due to impressive eye sight, succeed exceptionally well in coloured water; canals are an ideal environment. Over a 20 year period they have successfully depleted many indigenous species across the midlands and the south.

A couple of big Zander from the Trent & Mersey Canal (i'm looking young)

I have eaten this fish many times and it is not that bad. As it is a carnivore and not a benthic forager (like a carp) there is no real problem with muddy tastes. People will say it’s bony, but it only has a similar bone structure to a sea bass. The scales are particularly abrasive so I would suggest skinning the fillet.

Zander In Bacon Wrap With Caramelized Chicory On Carrot Puree Recipe 

Zander fillets in cream and herbs 

Fillets of Gloucestershire zander with duck egg, asparagus and crayfish 


Tuesday, 24 November 2009

London's reliance upon the South West

Ok, so we can’t get ANY fish at all as the winds keep blowing but when all is fine London and the South really does rely upon the South West fish markets. Recent figures published in the Fishing News show quite how large the landings are at Plymouth, Newlyn and Brixham and to my joy Newlyn leads the way. Well done boys and if you could just make your minds up regarding market modernisation you may just keep this title.

Port          *Demersal   **Pelagic      Shellfish          Total

Newlyn     £7,866,615    £436,488   £1,704,632    £10,007,735

Brixham    £5,093,629    £157,528   £3,833,638    £9,084,795

Plymouth  £1,991,377    £2,709,280 £2,088,775    £6,789,432

*   Ground fish such as soles, skates etc
** Midwater fish such as mackerel and sardines

Saturday, 21 November 2009

My old vocation - rescuing fish

As many of you know I have a background in fish that stretches further than mongery. One of the most enjoyable parts of an old job was to get wet and dirty with the fish. I wrote the account below for my old fisheries management website that details how we removed the fish out of those canals you all drive over – enjoy.

The United Kingdom has a fairly extensive canal network with lengths from Exeter in 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 15 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 network. 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 twenty 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 at the top was taken at Farmers Bridge, Birmingham on the Birmingham & Fazeley Canal where extensive re-development work was being undertaken. A series of lock pounds were drained to allow bank side renovation to take place; the aim was 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 a 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 at bottom) 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 more silty sections, so jobs are commonly held up while complete sealing takes place.

These two images show the completed dams in place. At the top 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. Below 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 pictures givesa 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 top 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 bottom shows an electrofisherman (that's me) 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 above 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 (top) 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 (bottom) 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.

What 'Cod' the prize be?

Roll up roll up come and get your raffle tickets. Bottle of wine? Box of chocolates? Cuddly toy? Oh no in a strange twist of events The Marine and Fisheries Agency have decided to pop all the members of the under 10 metre vessels fleet into a hat for a draw with the prize being 18 tonnes of Eastern Channel Atlantic Cod. Of course small print is in place to be eligible but 36 of those lucky enough to be in the hat will be rewarded with a catch limit of 500kg of cod each to be caught between the dates 1st -31st December.
‘Before starting to fish for their 500kg of cod winners will have to receive an EU log book and permit letters'
How bizarre is all this? Why could anybody think the allocation of fish quotas in this day and age is dated when such games are used to decide people’s livelihoods? Not to forget the sleepless nights poor Charles Clover will have when he finds out “his fish” are been given as a prize in a raffle!!

Sunday, 15 November 2009

Fish Locomotion

Fish species are present in many varying forms all over the world. The main difference between shapes of individual species would firstly be concern the need for them to travel through a fluid with varying densities pressures and drags. With a combination of these problems and in tern making best use of there form inside their chosen environment each species has developed, sometimes radically, different body profiles.

Species such as the rainbow trout (Oncorhyncus mykiss) have developed torpedo shaped bodies to counteract the drag confronted in a viscous fluid. Figure 1 shows the difference in streamline effects on two very different shaped objects in a fluid. The ideal situation to experience in a viscous fluid would involve laminar flow, this being smooth and thin with a creation of minimal drag. The circular shape in figure 1 is less streamlined in appearance and at the rear end turbulent flow is created. This is usually in the form of an eddy or wake and consists of a thicker layer, which increases the drag. For many fast swimming species the creation of a turbulent flow would result in the inefficient use of resources with respect to energy requirements. This may seem fairly straight forward but Blake (1983), suggests although the maintaining of a laminar boundary layer is a drag reduction system it happens to be less stable than a turbulent flow as it creates larger pressures upon separation.

Figure 1: Comparisons of flow around objects in viscous fluids. Source: Hosford (1997), p.16

As this is the case the inducing of a turbulent boundary layer can also reduce drag. It has been suggested that some species such as the mackerel (with the use of added dorsal fins), and the rainbow trout (with the use of an adipose fin) tend to induce a change in boundaries. Figure 2 shows that many years of development in aerofoil technology have created a design identical to the shape of a rainbow trout. The solid line is the aerofoil where as the dotted line is the trout. This concludes that the rainbow trout has formed into a highly streamlined structure.

The position of the shoulder will determine the type of flow over the body of the species. The shoulder of the trout is somewhat further back than the likes of the common bream (Abramis brama). This seems to verify that the form compares to the habitat and lifestyle of the species. The final point on the subject of drag would involve the use of the mucus covering the skin of the fish. The use of mucus in filling irregularities on the body could improve the flow characteristics of the boundary layers.

Figure 2: Comparison of a trout body form and a typical aerofoil. Source: Blake (1983), p.61

In normal observations fish swimming can be split into steady speeds, where the fish moves in one direction at a constant velocity or more commonly un-steady swimming which is the continuous changing of speeds and directions (Hoar, 1978). The critical speed of a species can only be measured from steady swimming but it is important to note that three other phrases, prolonged, burst and sustained swimming will take place in either of the firstly mentioned descriptions. It must be mentioned that potential growth response is effected by the cost of locomotion, which in tern contributes to the overall metabolic load (Ware, 1975), therefore efficient energy use is essential. Evidence has been found that juvenile fish do feed by moving at the appropriate speed to maximise their production rate (Ware, 1978). Figure 3 shows the fatigue curve of a rainbow trout (formally Salmo gairdneri). It clearly defines the three states of swimming used by all species of fish. Sustained swimming includes routine activities such as schooling and cruising and can be maintained in excess of 200 minutes. Prolonged swimming can continue between 200 minutes to 15 seconds and entails cruising with short bouts of vigorous movement. Burst swimming is the most inefficient form of activity with respect to energy use and can only be achieved for short periods of up to 15 seconds (Wilson, 1994).

Figure 3: Fatigue curves Source: Blake(1983), p.38

The rainbow trout can be classified into the group of subcarangiform fishes. This defines the type of body movement the species experiences when swimming. Most fish species swim with lateral body undulations running from head to tail. These waves run more slowly than the waves of muscle activation causing them, reflecting the effect of the interaction between the fish’s body and reactive forces from the water (Wardle, 1995). The undulations of the side to side movement in the body are slight in the anterior but there is a significant increase in the rear half to third of the body. The snout of the fish does not travel in a straight line but tends to oscillate at small amplitudes along the mean path of the fish (Hoar, 1978). Figure 4 illustrates this type of movement and clearly shows that no part of the body travels in a straight line, but tends to follow a curving path through the water.

Figure 4: Body propulsion of subcarangifom mode. Source: Hoar (1978), p.10

Only at speeds of under 1 to 2 body lengths per second does the amplitude of the body undulations change, usually there is no change with swimming speeds. The frequency that the tail beats and the velocity at which waves are passed to the rear of the fish directly effect the speed of the fish. Speeds of up to 25 body lengths per second have been recorded for fish below 1 metre in length. Although this measurement is for fairly small fish, Webb (1975) discovered that maximum acceleration rates for rainbow trout (40-50cm/sec2) were in the same order for other fish from a wide range of sizes. This suggested that maximum acceleration rates may be relatively independent of size. Although acceleration and size may not be comparable the wavelength of the body undulations remain constant when relative to the body length within species. When the size of the fish increases the attainable maximum frequencies decrease. In relation to tail beats and swimming style, Webb (1991) found that over a period of 226 completed tail beats from trout no constant speed was registered. Figure 5 shows the results and clarifies that sustained swimming is never constant and will always involve acceleration, deceleration or turning.

The caudal fin is probably the most important attachment used for acceleration. During Webbs (1977) experiment involving fin amputation of rainbow trout he clarified that the large caudal fin is required for maximum acceleration performance and creates the majority of generated thrust during fast starts. The dorsal and anal fins are also important in generating thrust but they are not as nearly as significant.

Some of the important aspects involving the movement of trout have been discussed, finally but just as significant is the production of energy needed to create these exercises. The thrust force of the fish is produced by contractions of the propulsive musculature. The velocity that the muscle contracts dictates the power that the fish can produce. Muscle structures of fish can be split into white and red types. Red muscle consists of up to 20% of the total belonging to the trout (less for lower active species such as carp (Cyprinus carpio)). This muscle has a low rate of fatigue and is used for all of the low speed sustained cruising. The white muscle fatigues more rapidly but gives maximum power output, which is used for burst speeds. Due to the speed of fatigue the white muscle can be used only for short periods of time.

Blake, R.W. (1983). Fish locomotion. Cambridge university press, Cambridge.

Hoar, W.S., and Randall, D.J. (1978). Fish physiology, volume VII: Locomotion. Academic press, New York.

Hosford, M.B. (1997). Fluid dynamics of ship resistance and propulsion. Institute of marine studies, Plymouth.

Wardle, C.W., Videler, J.J., and Altringham, J.D. (1995). Tuning in to fish swimming waves: body form, swimming mode and muscle function. Journal of experimental Biology, Vol 198, p. 1629-1636.

Ware, D.M. (1975). Growth, metabolism and optimal swimming speed of pelagic fish. Journal of the fisheries research board of Canada, Vol. 32, p. 33-41.

Ware, D.M. (1978). Bioenergetics of pelagic fish: Theoretical change in swimming speed and ration with body size. Journal of the fisheries research board of Canada, Vol 35, p. 220-228.

Webb, P.W. (1975). Acceleration performance of rainbow trout (Oncorhyncus mykiss). Journal of experimental Biology, Vol 63, p. 451-465.

Webb, P.W. (1977). Effects of median-fin amputation on fast start performance of rainbow trout. Journal of experimental Biology, Vol 68, p. 123-135.

Webb, P.W. (1991). Composition and mechanics of routine swimming of rainbow trout, (Oncorhyncus mykiss). Canadian journal of fisheries and aquatic services, Vol 48, no. 4,

p. 583-589.

Wilson, R.W., and Egginton, S. (1994). Assessment of maximum sustainable swimming performance in rainbow trout. The journal of experimental biology, Vol 192, no.1, p. 299-305.