News Release From The Game & Wildlife Conservation Trust

Freshwater angling is one of the nation’s biggest participation sports and is worth over £3 billion each year to the economy. Because of this huge demand it is often necessary to supplement the wild brown trout population with stocked farmed trout and it is thought that at least 900,000 adult fish are now released into our rivers each year.

In addition to breeding and releasing adult fish, fishery managers stock rivers with farmed trout that are either unfed fry, (very young fish that have just developed beyond the egg stage) or slightly larger and more expensive fed fry. Another recent development is the use of incubator boxes, which are filled with gravel, placed in the river and then seeded with 10,000 – 20,000 trout eggs.  Once the eggs hatch, the young fry are able to leave the boxes and enter the river via overspill pipes.

The Game & Wildlife Conservation Trust has carried out extensive research on many aspects of trout stocking including the use of diploid (fertile) brown trout and triploid (infertile) brown trout and the research findings are now part of the Environment Agency’s brown trout stocking policy.  Carrying on from this important research, the Trust has recently initiated a new four-year research project to investigate which type of triploid fry stocking provides the best return to anglers –  either farmed unfed and fed fry or unfed fry from an incubator box.  Also the research aims to measure any negative effects on native trout and the performance and cost effectiveness of incubator boxes.

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Scientists from the Game & Wildlife Conservation Trust are carrying out a four-year investigation into the best juvenile brown trout stocking practices, including the use of incubator boxesDylan Roberts, who heads the Game & Wildlife Conservation Trust’s fisheries research said, "Stocking with juvenile fish involves less financial investment and may result in more challenging fish than their farmed adult counterparts.   But stocking with such young fish might result in a low rate of return as mortality is high during this critical period of a trout’s life.  We are also concerned that stocked fry that survive to adulthood in a river may have more of an effect on the survival and growth of resident wild brown trout because they are more naturalised and feral and could thus create a greater window for potential impact.  

The Environment Agency has also announced that by 2015 all stocked trout must be triploid (infertile fish) or of native origin and stocked from a suitable rearing regime.  It is therefore important to carry out this research to ensure that all future fish stocking is sustainable and that it has minimal impact on the existing wild trout population."

At the end of this four-year research project, which is using different study sites on rivers in Dorset, the results will help fisheries managers to employ the best juvenile brown trout stocking practices for the benefit of anglers and the wild trout population.  The study will also measure the cost effectiveness of stocking with juvenile fish compared to adult triploid trout.

Dylan Roberts explains the value of this new study, "Catch-and-release angling, particularly for wild fish is becoming more popular, but there is not yet enough recruitment of wild fish to satisfy demand.  It is therefore necessary to stock rivers with farmed fish.  Our new study will assess the various techniques being currently used by fishery managers and make recommendations as to which stocking practices improve survival rates of stocked fish while having least impact on the wild population."

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