Error
  • JUser: :_load: Unable to load user with ID: 405
Thursday, 14 March 2013 09:18

Fishery management

Written by 
Rate this item
(1 Vote)

Even natural beauty such as this can be ruined with overstocking. By managing the fish population properly, the waterways can be preserved. Overfish & overstock and this would be a mud pool in no time.Even natural beauty such as this can be ruined with overstocking. By managing the fish population properly, the waterways can be preserved. Overfish & overstock and this would be a mud pool in no time.Unfortunately there are very few wild, pristine waters such as this left - all it takes is a combination of ignorance and disregard for the environment and this too will follow the route of so many venues.

The reason I'm discussing it this month is that we've just finished the first phase of population control on one of our waters, which due to receiving a longer lease, has encouraged us to begin a more proactive approach on managing the water for the members, safe in the knowledge that our efforts will be well rewarded in the long term.

The actions that we are taking can and should be done on all small scale waters, particularly on those where the activity on the water can be controlled - especially in terms of access control that ensures visitors follow the rules.

Over the years we had managed and taken care of the venue from an aesthetic aspect, ensuring that the grassland was undisturbed, preserving the fauna and flora within our area, insisting that anglers keep within the specially demarcated areas and so on.

A little basic knowledge and understanding of how a water system works will stand you in good stead. In terms of our needs we are obviously discussing Carp waters only, with other species requiring their own approach.

 

This Carp was caught at what used to be one of our top angling waters. Pollution, overstocking, in-breeding and poor management at its best.This Carp was caught at what used to be one of our top angling waters. Pollution, overstocking, in-breeding and poor management at its best.

Carp are prolific breeders, with females in their prime laying around something like 50 000 eggs per kilogram body mass during a single spawn – it is this fact that gets everyone in a panic about the potential population explosion within a water.

In reality though, the eggs first need to be fertilized by the males, which in itself is a fairly haphazard affair, with the eggs deposited by the females within the shallows amongst the grass, followed by the males, milking up the area where they were scattered. This results in many eggs being left sterile, with others open to predation from a variety of species of fish, crustaceans, birds and reptiles. Even after this a number of eggs will still fall victim to disease and infection.

So if you start off with around 350 000 eggs, and lose 25% for these reasons, plus a further reduction due to a natural hatching ratio of 70%, and a further 5% from natural deformity during birth, you’r left with a survival rate of around 50%.

That is still an awesome number of Carp – and even if you take into account the further reduction in numbers as the fry are consumed by predators reducing the numbers by another 75%, you still have thousands of fish from one female during only one spawning period. It is easy therefore to see how a water can become overstocked very quickly.

If we disregard these scary figures for a moment to focus on how a water maintains itself naturally, in its own equilibrium, the numbers won't matter due to a simple cause and effect.

A dam can only support a certain number of fish, simply because of the amount of food it holds. The size of water and population are also important, but the available food source is the most critical. If a dam can produce 10 tons of food per month, in all the forms the Carp can eat, this will be its maximum food production level, and the dam will peak with carp when this quantity of food is reached. It will obviously fluctuate - increasing and decreasing - but we'll use this as a base for this example. If the fish consume more than this, some will die; fewer fish will consume less, they will grow in size and number until the maximum consumption rate is reached and the natural food chain of the water will be complete.

Seasonal and general fluctuations will have an impact from time to time, so introducing more or less food. In extreme cases, such as droughts, there will be a major impact and possibly reduce the entire stock levels by 90%, while in times of plenty there with be a boom in population. But, after the situation returns to normal after a severe drought, an extraordinary amount of food and space becomes available for those that did survive, and for those still to enter the system. In a natural environment it is these types of events that in time can produce natural big fish venues.

 Focusing back on our sample water, an adult Carp eats on average around 2% of its body weight in food a day, which means a 20lb/9kg fish will consume 180g per day of food, or 54kg per month.

If the dam can sustain the consumption of the 10 tons of food a month as mentioned, the dam can sustain 185 Carp all weighing 9kg, or 370 fish of 4.5kg or any variation thereof, so long as they don't exceed the amount of food available.

Any change in the numbers will have an impact, but the dam has a certain threshold of available food, which cannot change naturally. It is for this reason that you often hear comments such as: “the water is over 50 years old and I caught a 10kg fish there 20 years ago, so the fish must have growth since then - they should be monsters!”

I've heard it plenty of times. The fact is, the dam will still hold fish to 10kg, and will do for the next 100 years unless something else has changed within the water to cause them to grow bigger, such as fish removed or died or the food source has improved.

 In our imaginary dam, if I want to improve the quality of my fish I will need to manage it, by either supplementing the food (which happens on many UK waters) in the form of angler’s baits, or reducing the numbers of fish it contains.

 Feeding a dam can be an expensive undertaking, so the only real option is to remove the excess fish. By removing 80 fish from our imaginary dam 4.3 tons of food per month will be freed up, which will then be available for those left behind.

 What also happens though is that the fish cannot consume all the food at once, which means much will be left over, which then opens a window for new fish coming throughout the year from any spawning taking place. Freeing up food like this will pack on weight for the bigger residents, but will also open the door for the smaller 1kg fish to flourish.

 You will now have a two- tier system, namely fish at 9kg growing on, plus loads of small fish coming through and also growing at a faster rate than the larger fish because they consume more, namely up to 5% of their body weight during early development.

 Here is the bottom line: to continue to improve the water these smaller fish MUST be removed on an ongoing basis.

 It’s for reasons like this that commercial fisheries in the UK and elsewhere have growing pens or ponds where the fish are artificially bred to certain weights and then stocked into waters at the weights needed, and in many cases the waters are man made with the fish manually stocked. In other instances existing waters are firstly drained, then shaped with large CAT diggers to create features and then re-filled and re-stocked. This type of fishery creation is very popular overseas, but in my mind it is quite difficult to be both an angler who enjoys his fishing who then becomes a fishery creator to go on and continue enjoy fishing it! I wonder if Gary Player or Jack Nicklaus prefer playing the golf courses they've created or those designed by other people..?

 Our target at the lake was the removal of 1 ton of fish, which we fell short of on the two trips we had set aside. It's “Murphy's Law” - when the water is quiet, one peg can catch 65 fish for the weekend, but with a dam full of lines, 40 fish per weekend for the entire bank was the order of the day!

 The good thing though about catching out the fish was that we could be specific about what we returned, so all fish over the 5kg mark were returned, as were all the Mirror and Linear Carp, regardless of size. With a couple of additional fish-out required we will meet the target, and within a year we'll be expecting some of the residents to peak out at around 18/19kg. To combat the small ones expected to come through,  a technique of electro-shocking will be used, which will focus specifically on the small ones. This is more technical than fishing them out, but the way I understand it, depending upon how high the current or voltage that is used, only fish to a certain size will be affected, so you will be able to shock and incapacitate the smaller ones, while the larger ones will swim away. I'm not fully up to speed on how it actually works, so will report back once the professionals have given us a practical demo on the system.

 Naturally there are many other aspects to managing and maintaining a productive Big Carp fishery, but for a start, the stocking levels of the water have to be the most important.

“Its a fine line between fishing and camping with a line in the water.” - Unknown.

Read 1267 times Last modified on Friday, 15 March 2013 11:34

John is a specialist Specimen Carp Writer who was instrumental in establishing specimen carp angling in South Africa.