With an estimated four million people fishing each year, it seems that angling has overtaken football as the nation’s favourite sporting pastime. Worth an estimated £3.5 billion, angling not only brings social and economic benefits; it is, according to the Game & Wildlife Conservation Trust also very good for the environment too.
However, to maintain the sporting viability of many rivers it is often necessary to augment wild fish stocks with stocking farm-reared fish. A study by the Game & Wildlife Conservation Trust (formerly The Game Conservancy Trust) suggests that approximately 344 tonnes of brown trout are stocked annually, which equates to about 750,000 takeable farmed brown being released into our rivers. In recent years many concerns have been expressed that stocking rivers in this way might pose a risk to the wild trout populations through interbreeding, competition for food, or they could attract an influx of predators.
In response to these concerns and as stocking is becoming more of a necessary option on many rivers, The Environment Agency in its National Trout and Grayling Fisheries Strategy produced in 2003, proposed that increased restrictions should be imposed on stocking rivers with fertile diploid fish, and instead using sterile all-female triploid trout in order to prevent farmed fish interbreeding with wild trout which may reduce the genetic fitness of wild fish.
As the majority of stocked fish are diploid, it would require a major shift in production practices to encourage a wider use of triploid brown trout. To understand whether increased use of triploids would be the best solution the Environment Agency commissioned the Game & Wildlife Conservation Trust to carry out a series of studies to address many of the concerns being raised about stocking.
Dylan Roberts, head of fisheries research with the Game & Wildlife Conservation Trust said, “If there is to be a radical change in fisheries management then it is essential that this is supported by scientifically-backed research to determine whether this will have an impact. This is one of the largest trout management investigations ever conducted in this country and it should help guide future policy.”
This important two-year study was carried out across 90 river sites. Dylan explains, “In total our study involved stocking 2000 diploid and triploid brown trout a year for 2 years into upland rivers including the Honddu in mid Wales and Arrow in Herefordshire as well as lowland chalk streams including the Allen, Frome, Piddle and Avon in the south of England. We investigated the performance of diploid and triploid brown trout, and their effects on wild brown trout and interactions between the three types of trout during the spawning season.”
This detailed study, which employed some novel research techniques, included a large-scale electro-fishing programme on stocked and control sites on upland and lowland rivers; radio tracking to determine the migration and spawning behaviour and an angler survey to measure the catchability and angler perception of farmed diploid and triploid brown trout.
Dylan Roberts, said, “The conclusions of each study highlighted that wild brown trout are indeed pretty “street-wise” compared to farmed fish and can hold their own. Generally in each of our studies stocked fish, particularly , in the harsher upland rain-fed river showed overall poor performance, and even in high stocking situations, there was no evidence to show that stocked fish have an impact on the growth, abundance and diet of wild brown trout.”
From a fisheries management perspective, the study revealed that there was no reason why farmed all-female triploid brown trout should not be used as a fishery management tool in order to conserve the genetic integrity of wild brown trout.
Importantly, even anglers agreed that there was no discernable difference. Dylan explains, “From the angler’s perception study we carried out on the River Avon in Wiltshire, the Trust’s research showed that when equal numbers of farmed all-female triploid and diploid trout were blindly marked and stocked simultaneously in the fishery, the anglers discovered that there was no significant difference between the two groups for condition or fighting ability. In addition, the study showed that triploid brown trout are an equal quarry and possibly more susceptible to capture compared to mixed-sex diploid brown trout.”
Now that this research has been concluded the Environment Agency will be considering the results and incorporating the recommendations in its National Trout & Grayling Fisheries Strategy. Dylan Roberts concludes, “The Environment Agency has to maintain a fine balance between conserving our wild stocks of brown trout while enhancing the fishing experience for anglers. The extensive data gathered from our research should help to guide the EA’s policy as well as providing practical guidance to fishery managers in the future.”
