Most of us at some time or other have dreamed of owning and running our own fishery. In this new series of articles, fishery owner Matt Collins gives us an inside view of what it’s really like to own and run your own fishery.
In this first part, Matt takes a look at what things you need to consider to keep your carp healthy.
As carp anglers, we feel a responsibility towards the carp we catch. We treat their wounds and mouths and make sure they spend as little time away from the water as possible. As a carp angler and now a fishery manager, I have an even greater appreciation of what is required to make sure that the carp live in a healthy environment.
When we first bought our French fishing holiday venue, we knew nothing about fishery management and how to look after carp. Looking back now, we are truly terrified by our lack of knowledge. Fortunately ignorance is bliss and we ploughed on regardless, making mistakes and learning on the job. Five years on and with a better understanding of what good fishery management is, I want to give you a look behind the scenes at what fishery managers need to do to maintain a healthy environment for the fish.
Food & Light: The fundamentals
As an angler I love a beautiful tree lined lake but too many trees are actually bad news for the fish because they block sunlight. Sunlight is the driving force behind any healthy aquatic system. Without it, there is no energy to power phytoplankton such as algae which is one of the main producers of oxygen within an aquatic system.
As well as producing oxygen, phytoplankton is a food source for zooplankton such as daphnia which in turn is an important natural food source for the fish.
When we first took over the management of our lake, our first task was to remove trees on the southern side of the lake to allow more light to reach the water. Over time this has increased oxygen levels and enabled the water to support a larger biomass of fish.
A Stable Environment
Carp need stable conditions to thrive and changes in pH levels can cause stress and put them off the feed. The ideal pH range for a carp lake is between 8 and 9 (7 being neutral and 6 being acidic). Rain is slightly acidic and will bring the pH down in a lake. Another contributing factor is leaf fall.
On many waters, carp can become harder to catch through the months of October and November as some types of leaf fall reduce pH levels. When leaves breakdown, they consume oxygen and it’s common to see oxygen levels fall simultaneously with the pH level.
Another reason for managing the number of trees around a carp lake is to reduce leaf fall into the water and therefore limit the pH decline in the autumn. Some trees are worse than others. Leaves from poplar trees take a very long time to break down and also acidify the water when doing so. Unsurprisingly, poplars are number one on our felling list every year.
A Clean Lake Bed
Over time the breakdown of leaf and other organic matter will create a layer of silt on the lake bottom. All lakes have silt. Some silt such as aerobic silt which contains oxygen is good and provides a home for blood worm and other larvae which is a rich source of food for carp.
However, as silt depth increases, it becomes anaerobic (i.e. does not contain oxygen). Anaerobic silt doesn’t break down naturally and left to build up over time can choke a water to death.
The only effective method for treating large areas of anaerobic silt is mechanical removal. We used a 30 tonne JCB with a massive 18m arm to remove 3000 cubic meters of silt from our lake. It’s a very expensive technique but vital to protect the future of the venue. On an ongoing basis, silt levels can also be controlled by adding silt traps to any in flows. We did this by installing two weir boards to our inlet stream.
Every few years the stream is dug out to remove the silt. We also changed the way the outflow works to suck silt up from the bottom and over the outflow. Silt can also be treated chemically on an annual basis with powdered lime.
A Balanced Biomass
A healthy lake needs to have a good mix of fish species as each one contributes to a balanced ecosystem. Perch are useful as they are the first fish to feed on daphnia in the spring. Roach are also very fond of daphnia. Without sufficient levels of perch and other silvers, and given the right climatic conditions, the daphnia population can explode and this can cause a rapid depletion in oxygen levels.
As roach and perch breed easily, you should also have a good head of small predators to keep their population in check. Pike are quite lazy, ambush style predators and of little use as a method of population control. Zander are very aggressive hunters and do a far better job of controlling the roach which is why we favour zander over pike.
Contrary to popular belief, catfish are not very effective at controlling a population of silver fish. Like pike, they are lazy by nature and often prefer a nice easy meal of pellets and boilies than the effort required to chase a small roach. However, catfish breed prolifically and left unchecked will quickly overrun a water.
Carp are a very successful species and given the right circumstances can breed prolifically. No one travels to France to catch singles and doubles so it’s important to remove these. Some fisheries are run along similar lines to monoculture farming, i.e. carp only with no others species. Such venues run a higher risk of fish kills as there are no other species to provide a stabilising effect to the environment. A regular netting program will help re-balance the lake with the adequate quantity of each species.
A Quality Feeding Programme
Depending on the biomass of the lake, the combination of natural food sources and anglers’ bait may not provide enough nutrition for the carp and you need to implement a good supplementary feed program.
The amount of food is calculated as a percentage of biomass per day. These percentages are governed by water temperature. During the winter when the lake is below 6 degrees, supplementary feeding is unnecessary. If we were growing carp commercially, when the water temperatures hits 18 degrees, the carp would eat up to 3% of their biomass per day which is an enormous amount of food. In a fishery environment, 1% of biomass per day is adequate to maintain health and growth.
Take the example of a ton of carp in a lake, this means that the carp need 70kg of bait and/or supplementary feed per week. This may seem like a lot of food but I can assure you it’s nothing to a healthy population of carp and they could get through three times that if we gave it to them! This does not mean that you need enormous quantities of bait to catch carp but you will have to strategically apply whatever you have in order to keep some bait over your rigs while fishing.
Good water quality, good food and a good balance of species are the main factors that contribute to the wellbeing of our carp. Sounds simple but it isn’t. It is a very delicate balancing act as working with nature is never an exact science. It is also massively rewarding to see the results of your efforts when healthy looking specimens are caught and returned safely to the water.