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Conservation & the Environment


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To maximise the pond production, a technique called 'polyculture' is used, which involves stocking the pond with a mixture of bottom, mid-water and top feeding fish. Typically, ponds are stocked with Barbel, Crucian Carp or Tench (bottom feeders), Chub, Dace, Roach or Bream (mid-water feeders) and Rudd (top- water feeders). This mix of species at three different levels ensures that all the available natural food such as Bloodworm (midge larvae) and Daphnia (water fleas) are eaten and production is maximised.


Harvesting The farm covers 4 Hectares, has 32 mature ponds ranging in size from 250m2 to 5000m2 Air injector aerator.


injectors" aerators for the larger ponds. These units also provide a substantial horizontal flow, which increases the "fitness" of the fish and helps them to adapt to life in rivers.


Into the Ponds


The ponds have to be prepared in readiness for the fish larvae. They are filled 2 to 4 weeks before the predicted stock-out date of the larvae, allowing time for the natural food to develop and are often enclosed in polythene tunnels to increase the water temperature.


Into the second year and the ponds are larger and deeper, up to 5000m2 in size, but prepared in much the same way. The ponds are emptied over the winter, excessive silt build up is removed and the remaining silt deposits are raked either by hand or machine to a depth 5cm to 10cm. This also helps to oxidise the deposits and release nutrients locked up in the mud. 2 to 3 weeks before the ponds are filled, quicklime is added, which further improves the mud and ensures that all pathogens and invertebrate predators are killed off.


Early spring and dried poultry waste is once again added to encourage the growth of a zooplankton culture over the following 8 - 10 weeks. Once the zooplankton bloom has matured the fish are introduced for the start of their second growing season.


At the end of growing season, the total weight of fish can typically have increased 10 fold.


Seine nets are used to harvest the fish


They are then transported to the holding tanks using, trailer mounted, aerated tanks which hold up to 5,000 fish. The holding tanks hold up to 10,000 fish and have clean water flowing through them. They are left undisturbed for at least 24 hours to remove any silt and mud which has clogged the gills, and to evacuate the gut of any ingested mud or food.


cont.... 10,000 fish stocks for the North East


In July, Calverton supplied rivers in the north east with 10,000 grayling in a bid to boost natural populations of the species.


Dried poultry waste is used to promote the growth of algae, which is in turn preyed upon by zooplankton which are eaten by the larvae. Survival rates up to the end of the first summer usually range between 80% and 95% depending on species.


The grayling are one year old and will continue to grow in the river and some of them will begin to spawn in the spring of 2013. It is hoped that by stocking these young fish over the next few years, the population of grayling in the river will return to healthy numbers. The Environment Agency releases fish into our waterways annually. Fisheries officers target fish stocking activity using data from local fish surveys to identify where there are problems with poor breeding and survival.


These rivers, like many, have suffered from poor water quality and habitat degradation in the past, but a concerted effort by the Environment Agency is helping to turn these watercourses around.


The Clow Beck flows into the River Tees near Darlington and has recently had two fish passes constructed and 2km of habitat improvement for grayling, created by the Environment Agency and the Tees Rivers Trust.


The EA are busy revitalising 9,000 miles of rivers by 2015 which will include habitat creation for endangered species such as water voles and fish passes to help fish navigate man-made obstacles like locks and weirs.


Environment Agency Fisheries Officers Paul Frear and Chris Carter will be introducing the grayling to their new homes. Chris said: “We are pleased with the way the restoration of these watercourses have gone and it is now time to help fish stocks recover. “It is good news for local anglers as there should be a wider variety of healthy adult fish to catch in coming years.”


Ben Lamb, from the Tees Rivers Trust said: “The introduction of the grayling into Clow Beck is great and the work by both ourselves and the Environment Agency will give this species a kick start in the watercourse. “Over the next three years we will be monitoring fish populations and invertebrates in the beck and we will be able to track the success of the grayling and their subsequent generations.”


The ponds are harvested during the autumn, using a seine net specifically designed for the purpose. This catches the majority of fish and the remainder are caught as the ponds are drained.


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