Managing a fishery requires many skills to get the results needed to maintain a good environment for fish and the angler a like. With our climate always changing these days the wildlife has also changed dramaticaly especialy the Cormorant population which seems to be on the increase every year!
I first stocked the lake with several hundred 6-8" King Carp I knew
very little about the Cormorants that come in land in search of food. The
Cormorant is a large black sea bird that can desimate the small fish stocks
in lakes and rivers!
A few times a week I would visit the lake to check on the progress of the fish and also to check the pH, Oxygen and Nitrite levels. On occasions I noticed a large black bird would take off as I walked down to the waters edge, the bird turned out to be a Cormorant! After some research I soon realised something had to be done to protect the fish before I lost them all to this flying predator.
I used various scaring methods like CDs on poles, wind socks and silver foil. The best result was from the wind socks placed around the lake. We also erected several posts around the perimeter of the lake and attached nylon strings to form a mesh to cover the surface, preventing any Cormorants from landing. Unfortunately this was not 100% effective either.
In the spring I deicided to net the lake to see how many carp had survived. After two goes with the seine net we counted approximately two hundred carp varying in size from 6-14". Quite a few had either slipped through the net or had been eaten.
With all the problems that can be encountered with stocking large carp like Spring Carp Mortality Syndrome i wanted to only use small carp and grow them up, but with the cormorants eating the small carp this was a problem. I contacted a fish farming friend who has lots of experience with recirculating systems and soon had a system designed with the purpose of growing 4-6" carp on over the winter to a size that the cormorants would not be able to eat in the spring.
When all the conditions are at optimal levels the Carp will eat, eat and eat some more but the more they eat the more toxic waste they produce from the food they are eating. To keep the water free of the waste products a filtration system is needed to brake it down and create a healthy environment for the fish to grow. The filtration system I have was designed to handle up to 5kg of food a day!
To get the system up and running i purchased 50 mixed ghost and common carp and after quaranteening them they were transfered to one of the main tanks to see how things would go.
After 3 months the filter was maturing and the feed was gradually increased as the fish started to grow. Even though i have been keeping Koi for some years and have qualifications in fish health and water quality I learnt a lot over the first 3 months as several problems cropt up with Nitrite and water levels in the tanks. I kept a record of all the levels and any other information which made it easier to identify when a problem occured and why. Now that the sample fish have grown any that are of a suitable size can be tranfered to the lake and the main stock will now be prepared for the system ready to grow on over the winter.