I

STATUS OF RAINBOW TROUT IN SCOTLAND: The Results from a Questionnaire Survey

Fisheries Research ServicesScottish FisheriesInformation PamphletNo. 23 2003

SCOTTISH EXECUTIVEISSN: 0309 9105© Crown copyright 2003

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Contents

Executive Summary............................................................................................................... IV

1. Introduction....................................................................................................................... 1

2. The FRS Rainbow Trout Questionnaire ................................................................................ 2 2.1 Current Geographic Distribution of Scottish Rainbow Trout Fisheries................... 2 2.2 Fishery Citations.................................................................................................. 5 2.2.1. Suggestions for the future........................................................................ 7 2.3 The Stocked Fish ................................................................................................. 8 2.3.1. Sources of supply .................................................................................... 8 2.3.2. Sex and maturity status ......................................................................... 10 2.3.3. Stocking size .......................................................................................... 10 2.3.4. Stocking levels ....................................................................................... 11 2.4 Natural Reproduction ........................................................................................ 12 2.5 Escaped Fish..................................................................................................... 14 2.6 Ecological Effects of Escapes............................................................................. 14

3. Discussion....................................................................................................................... 16 3.1 Stocked Waters ................................................................................................. 16 3.2 Stocking Practices............................................................................................. 16 3.3 Spawning Success ............................................................................................ 17 3.4 Reasons for Poor Spawning Success.................................................................. 18 3.5 Ecological Impacts ............................................................................................ 19 3.6 Diseases and Parasites ..................................................................................... 20 3.7 Demand for Rainbow Trout Fisheries.................................................................. 20 3.8 Benefits to Predators......................................................................................... 21

4. Conclusions..................................................................................................................... 22

5. References....................................................................................................................... 23

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Appendices ......................................................................................................................... 24 A. Reported in Replies to the Questionnaire .......................................................... 24 B. Previously Known to the FRS Freshwater Laboratory .......................................... 25

IV

Executive Summary

• The use of rainbow trout for fish farming and for stocking of Scottish angling fisheries has grown

substantially since the last national survey of the status of the species was carried out in 1974.

• Following the widespread circulation of a questionnaire, between December 2001 and January 2002,

305 Scottish waters were identified as being currently stocked with rainbow trout. This figure may be

a substantial under estimate as private waters are less likely to have been reported.

• Annual stocking densities per hectare and average size of stocked fish have increased since 1974.

• Rainbow trout that had escaped from fish farms, or emigrated from stocked fisheries, were reported

from 54 rivers or streams, seven freshwater lochs and three sea lochs or estuaries where they had

not been deliberately stocked. This information was based on experience over several years, but the

inference is that these incidences are widespread.

• There is in Scotland only limited evidence of the successful reproduction of rainbow trout in the wild,

and no self-sustaining populations were reported in the survey. The current use of mainly all-female

and, to a lesser extent, triploid fish for stocking is a major constraint on natural spawning.

• Viewed in the context of conserving native stocks of fish, the colonisation of our waters by rainbow

trout is clearly not a high priority issue at present.

• With gradually changing climatic conditions, however, it is conceivable that the species could become

naturalised here eventually.

• Concerns remain about the ecological impact of rainbow trout on native fish and other fauna, where

they are heavily stocked, or where they have escaped in large numbers from fish farms.

• Intensively stocked rainbow trout fisheries are an important economic and recreational resource.

• Rainbow trout provide additional feeding opportunities for ospreys and other predators that are much

appreciated by the general public and tourists.

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This report describes the results of a questionnaire survey of the current status of rainbow trout (Oncorhynchus mykiss (Walbaum)) in Scotland. It is available on the Fisheries Research Services (FRS) web site (http://www.frs-scotland.gov.uk) in pdf format, and can be updated as required. A later report will address the ecological effects of rainbow trout in more detail.

Rainbow trout were first introduced to the British Isles successfully from their native areas in western North America in 1885 (Worthington, 1940-41; MacCrimmon, 1971) and used for restocking angling waters, where they soon became a popular addition to our game fish species. However, within the last three decades, there has been a large development of intensive farming of rainbow trout for the table market and a parallel growth in restocking fish of a takeable size for angling. Now, almost certainly, the majority of Scottish trout anglers fish mainly for rainbow trout. Intensive put-and-take fisheries have opened up throughout the country, supporting much higher cropping levels than would be sustainable in waters that have to rely upon natural production. Arguably, these commercial fisheries ease the strain of angling pressure upon more fragile populations of native brown trout (Salmo trutta L.). In addition, many anglers opportunistically exploit 'escaped' rainbow trout (see section 2.5) in rivers and more especially in some of the larger lochs that support large complexes of floating cage farms, such as Loch Awe, Lochy, Tay and Earn. Concerns remain about the possible ecological impact of these escapes. Many of these fish are easily recognised as being of reared origin because they have distinctly eroded tail and dorsal fins, but others with good fin definition could be derived from natural spawning. Yet in spite of the widespread occurrence of this introduced species in the wild, no evidence has been found that it is successfully colonising Scottish waters. Even so, the situation has to be reviewed from time to time, as the ecological requirements of rainbow trout are similar to those of our own salmonid fishes. Due to the high production capacity of the aquaculture industry and the potential for continuing escapes, together with changing climatic conditions, it is reasonable to believe that rainbow trout could eventually become established here. This report describes a review of the current status of rainbow trout in Scotland.

1. Introduction

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2. The FRS Rainbow Trout Questionnaire

The purpose of the FRS questionnaire was to consult fishery managers, owners and anglers throughout Scotland about their experience and views on rainbow trout. They were asked about the locations of rainbow trout fisheries, the extent of incidences of escapes and of spawning success of the species in the wild. In addition, fishery managers were asked to indicate their current levels of stocking and sources of stocked fish, where this information did not compromise them commercially. The answers were intended to be comparable with the results of a similar questionnaire survey of the status of rainbow trout in Britain and Ireland, carried out almost 30 years ago by the late Winifred Frost (Frost, 1974). In that survey, which was sponsored by the Salmon and Trout Society, 550 copies were distributed and about 200 replies received. For the FRS survey, approximately 1,000 reply-paid questionnaires were distributed in December 2001 and early January 2002, as shown in Table 1.

Approximately 350 replies (35%) were received. They provided further information on the names and locations of rainbow trout fisheries, levels of escapes and natural reproduction. More than 70 fisheries contributed to the survey.

2.1 Current Geographic Distribution of Scottish Rainbow Trout Fisheries

Three hundred and five Scottish waters were identified that currently contain stocked rainbow trout (Fig. 1). These are listed alphabetically in Table 2. Most of these waters are fisheries where the fishing is available on a day-ticket basis. Some of the fisheries are operated by angling clubs and associations for their members and visitors, and others are exclusive to syndicates, or individual owners and their friends. Waters stocked for private fishing are less likely to have been reported, as the owners or tenants may wish to maintain their anonymity as security against poaching. In addition, many of the fisheries comprised groups of ponds, or lochs. Therefore, the true number of rainbow trout waters in Scotland is likely to be considerably higher than that found in the survey. (See 2.2 Fishery citations).

TABLE 1The distribution of the FRS Rainbow Trout Questionnaire, 2001

Addressees Nos Source

Members of national angling associations 650 Scottish Anglers Nat. Assoc., Salmon and Trout Assoc.

Rainbow trout fisheries 170 Yellow Pages, WWW, guide books, etc.

Restocking trout farms 40 WWW, Fish Industry Yearbook 2001

District salmon fishery boards 50 Association of Scottish District Salmon Fishery Boards

Fishery Trusts, etc. 15 Scottish Fisheries Coordination Centre

Water Boards (for fisheries under their management) 15 WWW

Others 60 Personal contacts

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The waters were widely spread throughout the country. The main clusters were within ready reach of the presumed most important customer base for stocked fisheries in the more densely populated areas, such as the central belt, parts of Ayrshire, the south-west, Aberdeenshire and Moray. At present, there appear to be relatively few waters that are stocked with rainbow trout in the Highlands and the Hebrides and none in the Northern Isles.

Note: this is the current pattern of distribution and does not show the many more waters that have been stocked with this species in the past. For example, rainbow trout were stocked in the Town Loch near Lerwick, in the Shetland Isles, but have not been stocked there recently.

Figure 1:The Locations of Stocked Waters in Scotland Holding Rainbow Trout in 2002

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Achilty Loch Carlogie DamAchnaboban Carman ReservoirAcreknowe Reservoir Carsfad ReservoirAirthrey Loch Castlehill ReservoirAllandale Tarn Central Scotland Trout FisheryAltyre House Loch Clerklands ReservoirAntermony Loch Cleugh ReservoirApproach Loch Clubbiedean ReservoirArdgeith Clugston LochArdgowan Reservoir Cobbinshaw ReservoirAros Loch Coldingham LochAscog Loch Collenan ReservoirAvielochan CommoreBallater AC ponds Conaglean LochBallo Reservoir Corby LochBalnagown Loch Corriemulzie PondBangour Cowan’s LawBarcraigs Reservoir Coyle WaterBarnluasgan CragganBarnshean Craggie LochsBarscobe Loch CraigallianBeecraigs Craigdow LochBelston Loch Craigendunton ReservoirBhac Loch Craigluscar FisheriesBishops Glen Reservoir Craikaig PondBlack Loch (Bladnoch) CraudfurdlandBlack Loch (Cleish) Creoch LochBlack Loch(Dumbart.) Crombie ReservoirBlair Walker Pond CromlixBlairmore Crosswood ReservoirBlairs Loch Dalmigavie pondsBoath Loch DalreagleBottom Dam Dalvennan LochBowden Springs Dam LochsBowhill Lower Dargarvel LochsBowhill Upper Den of PhinellaBrahan Ponds Derclach LochBroom Fishery Dindinnie ReservoirBrother Loch Donolly ReservoirBruntis Loch Dornoch LochansBuittle Reservoir Dowally LochBurnfoot Reservoir Easter BaladoBurns Fishery EcclesgreigBush Moss Eddy LochButterstone Loch Ettrick LochCairnbanno Fad LochCairnsmill Fairliemoor ReservoirCameron Reservoir Fassfern pondCamphill Reservoir Fedderate ReservoirFern Loch Kettleton ReservoirFingask Loch Kilbirnie LochFitty Loch KillearnFodderty Ponds KindarFordie Pond King’s MyreFordun KingennieForgue KypesideFyntalloch LarbraxGadloch LawfieldGalston LedcrieffGartmorn Dam Ledyatt FisheryGeddes Lochs Leven LochGladhouse Reservoir Lilly LochGlen of Rothes Lindean ReservoirGlen Tanar LindoresGlenburn Reservoir LinlithgowGlencorse Reservoir Little LochGlendrishaig Reservoir Loch a ChaoroinnGleneagles lochs Loch an IasaichGlenfintaig pond Loch na CraigeGlenkiln Reservoir Loch na CrannGlenmazeran ponds Loch of BlairsGlensherup Loch of Loirston

TABLE 2Scottish Waters Currently Stocked with Rainbow Trout (2002)

Glentanar Lochs Loch RoisneabhatGlow Loch Loch ShankstonGolden Loch Loch SpallanderGrangehall Lochan an TuircHarlaw Reservoir LochenbreckHarpsdale Lochend LochHaylie Reservoir Lochllyoch ReservoirHeadshaw Loch LochoreHeatheryford LochterHelensburgh Reservoir LochuanaganHigh Dam LoganleaHillend Reservoir Lower FrandyHoll Reservoir Macbiehill EstateHopetoun Mains of PenninghamHospital Loch MarkleHowwood McKay’s LochInsch Meallbrodden LochInverawe MenteithInverdruie Mill of FortuneInverlochy Castle loch Millhall ReservoirInvertrossachs ponds Mochrum LochJerocho Lochs MoffatKendoon Monikie Island PondKinloch (private) Monikie North PondKintradwell Ponds Montague FisheryKirklegreen Reservoir Morton Castle LochKirkmichael Loch Morton FisheryKnockquassen Reservoir MossatKnowes Dean MossdaleMosston Muir Soulseat ReservoirMuirhead Reservoir SpallanderNeilston SpoutsNew Loch SpringwaterNewmill St Mary’s Loch, FordNewton Farm Stobo LochNorth Craig Reservoir Stoneyfield LochsNorth Third Strathallan Ochiltree StrontianOdly SwanswaterOrchill Loch TarboltonPalnure Tarvie LochsParkley Teasses FisheryPenwhapple Reservoir The FisheryPhones Loch Threipmuir ReservoirPinbraid Loch ThriepleyPiper Dam Tinto Trout FisheryPitfour Tomich Hill LochPolmont Reservoir Top DamPortmore Loch TorhouskiePort-na-Lochan TorlundyPowder Dams Trusta LochPrestwick Reservoir Tullich FisheryRaemoir Pond TurnberryRaith Lake Tweeddale MillenniumRaith Waters Unnamed LochRathen Reel Affair Upper Glendevon ReservoirRescobie Urray LochsRoan Vaa LochRoisneabhat Watch ReservoirRoseberry Reservoir WatersideRossdhu Pond WaulkmillRosslynlee Wee LochRothiemurchus Trout Fishery WeeglenamourRotmell Loch Westerton FarmRowbank Reservoir Whirr LochRusky Whiteadder ResSandyknowes Whitehills LochSeamaw Whitehills privateSeggat Wooden LochSelmuir Ythan ValleyShell Firewater Pond (private) Skelmorlie Snipe Loch

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2.2 Fishery Citations

Table 3 shows the number of times that individual fisheries were cited in the replies to the FRS survey. Two fisheries, Loch Leven (1,416 ha) and the Lake of Menteith (283 ha) were cited more than 100 times, and 27 fisheries 10 or more times.

TABLE 3Citations of Rainbow Trout Fisheries in Scotland 2001

Loch Leven 113 Watch Reservoir 9 Kirkchrist Fishery 4Lake of Menteith 106 Fairliemoor Reservoir 8 Middleton Fishery 4Butterstone Loch 71 Gartmorn Dam 8 Pitfour Fishery 4Loch Fitty 52 Heatheryford 8 Tweeddale Millennium 4Lindores Loch 52 Sandyknowes 8 Avielochan 3Portmore Loch 39 Allandale Tarn 7 Barnshean Reservoir 3North Third Reservoir 38 Ardgowan Reservoir 7 Loch Bhac 3Ballo Reservoir 30 Haylie Reservoir 7 Black Loch 3Piper Dam 25 Kingennie Fishery 7 Carman Reservoir 3Rescobie Reservoir 25 Markle Fishery 7 Dalvennan Loch 3Linlithgow Loch 23 Raith Lake 7 Drummond Fishery 3Frandy Reservoir 22 Loch Achilty 6 Glen of Rothes Fishery 3Monikie Reservoir 19 Clubbiedean Reservoir 6 Loch Glow 3Glensherup Reservoir 16 Glencorse Reservoir 6 Harpsdale Lochans 3Springwater 16 Lawfield Reservoir 6 Lindean Reservoir 3Swanswater 16 Lochter Water 6 Lochenbreck 3Coldingham Loch 15 Penwhapple Reservoir 6 McKay’s Loch 3Loch Fad 15 Bowden Springs 5 Loch Ochiltree 3Insch Fishery 15 Golden Loch 5 Roslynlee Fishery 3Morton Fishery 15 Harlaw Reservoir 5 Torlundy Fishery 3Beecraigs Reservoir 13 Hillend Reservoir 5 Waterside Fishery 3Cameron Reservoir 11 Inverawe Fishery 5 Antermony Loch 2Newton Farm 11 Stoneyfield Lochs 5 Approach Loch 2Orchill Fishery 11 Bangour Fishery 4 Ardeith Reservoir 2Cobbinshaw Loch 10 Cowan’s Law 4 Barcraigs Reservoir 2Howwood Reservoir 10 Coyle Water 4 Black Loch (private) 2Loch Rusky 10 Craigluscar Reservoir 4 Bruntis Loch 2Lochore Meadows 9 Craufurdland 4 Camphill Reservoir 2Millhall Reservoir 9 Easter Balado Reservoir 4 Clerklands Reservoir 2Moffat Fishery 9 Forgue Fishery 4 Clugston Loch 2Tarvie Lochs 9 Inverdruie Fishery 4 Collennan Reservoir 2Craggan Fishery 2 Stobo Loch 2 Craigdow Loch 1Loch Creoch 2 Achnaboban 1 Craigendunton Reservoir 1Cromlix Fishery 2 Acreknowe Reservoir 1 Crakaig Est Pond (private) 1Crosswood Reservoir 2 Airthrey Loch 1 Dalmigavie ponds 1Dornoch Lochans 2 Altyre House Loch 1 Daleagle Loch 1Loch Ettrick 2 Loch Ascog 1 Dam Lochs 1Fyntalloch Loch 2 Balnagowan (private) 1 Dargarvel Lochs 1Glentanar lochans 2 Barnluasgan Loch 1 Den of Phinella Fishery 1Holl Reservoir 2 Bishops Glen Reservoir 1 Derclach Loch 1Kettleton Reservoir 2 Black L. (Cleish) 1 Donolly Reservoir 1Kilbirnie Loch 2 Blairmore Fishery 1 Dowally Loch 1Killearn Reservoir 2 Bottom Dam 1 Drummond Loch 1Loch Kindar 2 Bowhill Upper Loch 1 Drunkie Burn ponds 1Lilly Loch 2 Bowhill Lower Loch 1 Dunoon Reservoir 1

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Lochlyoch Reservoir Brahan Ponds Dunskey LochsLochuanagan 2 Broom Fishery 1 Dunwhan Reservoir 1Mains of Penn.hm 2 Brother Loch 1 Ecclegreig Fishery 1Midmar Fishery 2 Buittle Reservoir 1 Loch Eddy 1Mill of Criggie 2 Burnfoot Reservoir 1 Fassfern Pond 1Mochrum Loch 2 Burns Fishery 1 Fern Fishery 1Mossat Fishery 2 Bush Moss Fishery 1 Fodderty Ponds 1Mossdale Fishery 2 Cairnbanno 1 Fordun Fishery 1Newmills Fishery 2 Cairnsmill Fishery 1 Gad Loch 1Loch Odly 2 Carlogie Dam 1 Galston Fishery 1Powder Dams 2 Castlehill Reservoir 1 Geddes Lochs 1Raemoir Pond 2 Cleugh Reservoir 1 Gladhouse Reservoir 1Rathen Reel Affair 2 Commore Fishery 1 Glenburn Reservoir 1Loch Roisneabhat 2 Conaglean L. (private) 1 Glendrishaig Reservoir 1Selmuir Reservoir 2 Corriemulzie (private) 1 Glenfintaig Pond 1Skelmorlie Reservoir 2 Craggie Ls (private) 1 Glenkiln Reservoir 1Loch Spallendar 2 Craigallion Loch 1 Glenmazeran ponds 1Grangehall Reservoir 1 Muirhead Reservoir 1 Un-named loch 1Helensburgh Reservoir 1 Neilston Reservoir 1 Vaa Loch 1High Dam 1 New Loch (private) 1 Meallbrodden Loch 1Hopetoun Lochs 1 North Craig Reservoir 1 Ledyatt Fishery 1Hospital Loch 1 Palnure Reservoir 1 Teasses Fishery 1Inverkeillour Lochs 1 Parkley Reservoir 1 Corby Loch 1Inverlochy Castle 1 Phones Loch 1 Fordie Pond 1Invertrossachs 1 Pinbraid Loch 1 Mill of Fortune 1Jericho Fishery 1 Polmont Reservoir 1 Kendoon Loch 1 Port-na-Lochan 1 King’s Myre Loch 1 Prestwick Reservoir 1 Kinloch (private) 1 Loch Roan 1 Kintradwell (private) 1 Roseberry Reservoir 1 Kirklegreen Reservoir 1 Rotmell Loch 1 Knowes Dean 1 Rowbank Reservoir 1 Kypeside Fishery 1 Seggat Fishery 1 Little Loch 1 Shell Pond (private) 1 Loch a Chaoroinn 1 Snipe Loch 1 L. an Iasaich (private) 1 Soulseat Loch 1 Loch na Crann 1 Spouts Fishery 1 Loch of Blairs 1 Strathallen Ponds 1 Loch nam Gillean 1 Strontian Loch 1 Lochan an Tuirc 1 Sweethope Reservoir 1 Loganlea Reservoir 1 Tarbolton Reservoir 1 Macbiehill Estate 1 Tomich Hill Loch 1 Maich Water 1 Top Dam 1 Mill of Elrick 1 Torhouskie Reservoir 1 Millbuies Fishery 1 Trusta Loch (private) 1 Morton Castle Loch 1 Tullich Fishery 1 Mosston Muir 1 Turnberry Reservoir 1

TABLE 3 continuedCitations of Rainbow Trout Fisheries in Scotland 2001

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Several factors may have influenced the frequency of the citations:

• The size, or the intensity of the fisheries and, therefore, the likelihood that the survey respondents would visit them.

• Copies of the questionnaire were sent to many secretaries of angling clubs which take part in boat competitions on the larger waters that hold rainbow trout, especially Leven and Menteith. Therefore, it is not surprising that these waters were mentioned so often.

• Larger clubs are less likely to visit the smaller fisheries, most of which lack boats, although individual members may do so. At the other end of the scale, some fisheries cater for syndicates or small clubs, so the chances of them being recorded are proportionately less.

While the larger waters were often cited, the majority of the smaller fisheries were cited only once (52%), which suggests that some are likely to have been missed.

2.2.1 Suggestions for the futureA more complete list of the fisheries could be compiled by surveying a greater number of individual anglers, in addition to clubs. Another approach would be to contact the supplying fish farms, but listings of their customers may be withheld for use as information that is commercial in confidence. Under the Registration of Fish Farm Businesses Order 1985, farmers are required to register their farms and businesses if they are trading in fish and to keep movement records. Movement records may be a means of identifying all of the stocked fisheries, but these records would have to include transfers of fish from elsewhere in the UK.

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X Controls On Transfers of Freshwater Fish in Scotland

Transfers of fish may lead to the spread of parasites or diseases, or have other adverse

ecological impacts. Under current fish health legislation, fish farmers are required to register

their establishments and are required to keep records of fish movements, including those into

fisheries. They must make these records available to Inspectors when asked to do so. In the event

of a notifiable disease being found or suspected, the Scottish Fisheries Minister may place an

Order to prevent movements of fish on or off the farm concerned. However, in Scotland, there is

no legal reason for fishery owners, or their suppliers, to identify the waters into which transfers

will occur, other than where they are required to meet conservation arrangements for SSSIs1. In

other circumstances, under the terms of the Wildlife and Countryside Act 1981, it is an offence to

release into the wild, or allow to escape without reasonable steps being taken to prevent it, any

animal that is not normally resident, or a regular visitor to, Great Britain. The stocking of rainbow

trout, on the other hand, may be exempt in that this species has been ordinarily resident here for

more than a century, although it is not generally established in terms of breeding success.

1 Sites of Special Scientic Interest

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2.3 The Stocked Fish

2.3.1 Sources of supply

According to the replies, most of the stocked trout came from Scottish fish farms, but some fisheries were supplied from English fish farms as far afield as Devon. However, insufficient replies were received to indicate the tonnage that originated from outwith Scotland. The locations of 44 Scottish fish farm sites currently rearing rainbow trout are shown in Figure 2. Annual production survey reports have been produced by FRS since 1979, the first containing information on the number of rainbow trout farms back to 1965. The earliest report detailing production tonnage split according to the restocking and tables trades was published in 1981. A total of 17 tonnes of rainbow trout were produced for stocking in 1980. The latest production figures for Scottish fish farms (Anon, 2001) show that almost 843 tonnes of rainbow trout were reared for restocking in 2000. The restocking tonnage in 2000 represents a fall of 14% on the previous year when the figure was 977 tonnes, although the trend during the last 10 years has been a rise in annual production. [Note that these figures represent the amount of fish stocked and not the catches.]

Figure 2:The locations of Rainbow Trout rearing sites

(from the FRS Scottish Fish Farms Annual Production Survey, 2000)

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In 2000, the total Scottish production was 5,154 tonnes, of which 4,370 tonnes (85%) was reared in fresh water. The largest fish farms specialise in rearing fish for the table. Forty-four percent of the overall production was in freshwater cages, 41% in ponds and raceways, tanks and hatcheries and 15% in seawater cages*. Nearly all of the production for angling use comprised trout in the weight categories 450-900 g, or greater than 900 g, that were supplied to a proliferating network of inland put and take fisheries. The production destined for the restocking of angling waters increased annually until 2000 and accounted for 16% of total rainbow trout production in that year. The production of rainbow trout in Scottish fish farms is very much less than that of Atlantic salmon (Salmo salar L.), which in 2001 was estimated to be in excess of 150,000 tonnes*. However, 90% of the salmon production was in the sea.

The growing importance of the Scottish rainbow trout angling fishery during the last decade is illustrated by comparing the tonnage produced for restocking with the total reported' all-methods' catches of salmon plus grilse (Fig. 3). The total amount stocked annually in Scotland in recent years, including fish imported from other countries in the UK, is likely to have exceeded 1,000 tonnes. No details of the economic value of the rainbow trout fishery are presently available, but it must be considerable. At least 1,000 full-time job equivalents are likely to be dependent on the national fishery. This estimate is based on a simple consideration of the number of identified stocked waters and the associated restocking and tackle trades alone, and does not take account of other downstream effects. However, the Scottish Executive has commissioned a national study of the economics of angling that may provide such information.

Figure 3:Rainbow Trout Restocking Tonnage and Total Salmon Plus Grilse Catch in Scotland (1993-2000)

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1993 1994 1995 1996 1997 1998 1999 2000

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Rainbow Trout Restocking Tonnage

Total Salmon plus Grilse Catch

*FRS Scottish Fish Farms Annual Production Survey, 2000

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2.3.2 Sex and maturity statusCurrently, many of the fish farms that supply rainbow trout for restocking use sexually modified fish. Not surprisingly, some of the fishery respondents seemed uncertain about the distinction between diploids, all-female diploids, triploids and all-female triploids. This means their answers to the questions about their sex and maturing status and implied spawning capacity are hard to summarise and should be treated with caution. Most believed their fish to be largely, or solely, all-females, and a few stated that they used all-female triploids, or just triploids. Only two believed their fish to be normal diploids. More robust information*, indicates that 82% of rainbow trout laid down to hatch in 2000 were all-females, only 6% were triploids and 12% were mixed-sex diploids. The survey report* states that the triploids were produced mainly for the restocking trade.

Sex Control of Rainbow Trout

Normal diploid rainbow trout (based on two sets of chromosomes) are expected to comprise roughly

equal proportions of males and females. This was how rainbow trout used to be supplied from

fish farms for restocking back in the 1970s and early 80s. Unfortunately, at that time, maturing

males (normally from age 2 winters) were caught in large numbers in the early part of each year,

when they were in poor condition for sport and eating. These male fish tended to be soft and slimy

and highly prone to fungal infection. Females tend to mature one year later, by which time most

have been caught, or have died. The development of technology to produce all-female batches

has addressed the problem of maturing males. All-females are supplied from specialised hatcher-

ies, where normal genetic females are mated with other females that function as males because

tiny amounts of testosterone have been added to their diet when they were early fry. The eggs

then lack the Y chromosome that would make half of them male fish. As a further development,

triploidising (generating three sets of chromosomes) by pressure-treatment of the recently ferti-

lised eggs, renders sterile nearly all (>90%) of the subsequent batches of fry. Some triploid males

continue to mature, although their testes are dysfunctional, whereas all triploid females are

sexually immature, with tiny ovaries. Triploidising all-female batches of eggs means that all of the

fish are guaranteed to be non-maturing females and none of their growth is devoted to gonadal

tissue. However, triploid fish are believed to be more difficult to rear and all-female diploids remain

the most common type of rainbow trout used for restocking.

2.3.3 Stocking sizeSixty-eight fishery managers commented on the size structure of the fish that they used for stocking. Forty-one fisheries (60%) mainly, or solely, stocked fish weighing less than 1 kg. According to comments received on the questionnaires, most of these fish weighed about 700-900 g. Twenty-four (35%) stocked mainly larger fish of 1-2 kg and three (5%) stocked only with specimens weighing more than 2 kg. Forty fisheries (59%) stocked some fish of this size. Rainbow trout weighing well upwards of 5 kg are commonly reported in the angling press every month in their reviews of Scottish put-and-take fisheries, as with similar fisheries in England and Wales.

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*FRS Scottish Fish Farms Annual Production Survey, 2000

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2.3.4 Stocking levelsSixty-seven fisheries commented on annual stocking levels. [Note that this is the total numbers of rainbow trout stocked in a year, not the numbers present at any one time. Many of the fish will be caught within days of stocking.] Figure 4(a) plots the annual stocking levels in relation to the surface areas of the fisheries. The annual stocking densities ranged up to more than 6,000 fish per ha, but further interpretation is difficult because of scaling effects due to the wide scatter in the size of the fisheries, which range from about 1 ha to more than 1,400 ha. Figure 4(b) removes the larger fisheries (greater than 50 ha), which makes it easier to see what is happening among the smaller ones that make up the great bulk of the survey. It is then apparent that the fisheries larger than about 5 ha tend to be stocked more lightly than the smaller waters, many of which have been excavated for the purpose, or are based on existing ponds.

The decision on the level of turnover of stock will depend more on the economics of the fisheries than on biological constraints. In the small fisheries, most of the surface area can be cast over by anglers. Therefore, the recapture rate is likely to be greater than in larger water bodies, where fish can move way from the banks. Deeper water is more awkward to fish effectively and boats may be required. Larger fisheries have to stand the extra expense of maintaining boats and engines and controlling poaching over a large, often unregulated perimeter, much of which may be open to the general public. Natural lochs, or reservoirs, contain existing fish communities with which the stocked fish have to interact. Often, rainbow trout are added to supplement catches of self-supporting populations of brown trout, and coarse fish species may be present as well. Stocking levels may be kept low to conserve these wild populations.

Figure 4(b):Densities of Rainbow Trout Stocked in Scottish Waters (in fisheries <50ha)

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Figure 4(a):Annual Stocking Densities of Rainbow Trout in Scotland

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2.4 Natural Reproduction

The overwhelming majority of respondents wrote that they were unaware of successful spawning of rainbow trout in their fisheries, or in ones that they visited. Some people had seen them spawning, but had found no subsequent evidence of juveniles. However, the managers or owners of 14 waters confirmed that successful spawning had taken place. These instances were observed mainly several years ago and most of the respondents referred to limited success and occasional, rather than regular, numbers of juveniles. The current widespread use of all-females and triploids must be a major constraint on the occurrence of natural reproduction. The questionnaire also resulted in 32 less conclusive reports of fin-perfect juvenile rainbow trout in fisheries where only larger fish were believed to be stocked. These small fish may be the result of natural spawning, or they could have been carried in the transport tanks and discharged unintentionally. One fishery had received a few salmon parr in this way. In some cases, the small rainbow trout could have come from a local hatchery or fish cages. For example, rainbow trout of initial weights at introduction of 10-20 g are grown on commercially in some cage farms moored in lochs. A proportion of these small fish may escape because of damage to the nets caused by storms, general wear and tear, bird strikes, human error, or wilful damage. Anglers have been known to cut the meshes to improve their fishing prospects. Fish that escape very early in their life in the cages are likely to have good fin conformation and, having grown on at liberty, may appear to be from natural spawning. Loch Awe was frequently mentioned as a place where natural spawning was suspected. However, juvenile electro-fishing surveys carried out by the Awe Fishery Trust have consistently failed to find any evidence of rainbow trout in the feeder streams to the loch (pers. comm. A. Kettle-White). Similarly, juvenile rainbow trout that escape from hatcheries and find their way to rivers can look like fish of wild origin. [Escapes are discussed later see p. 14.]

There is, however, no doubt that rainbow trout can sometimes spawn successfully in the wild in Scotland. In addition to the positive, but often inconclusive, responses on spawning mentioned earlier are another twelve waters where FRS FL staff can confirm that live fry resulted from natural spawning, although the survival level may have been low.

Table 4 categorises all of the known sites of spawning by the source of information (manager, angler, or FRS FL staff) and the resulting success or failure. The validity of any observed success is ranked as ‘High’ or ‘Low,’ based on the strength of the supporting information. Successful spawning could have occurred in the waters that are categorised as ‘Low’, but the indications of success need verification. More details of some of the instances of spawning reported in replies to the questionnaire, as well as some of those that were previously confirmed by FRS FL staff are given in the Appendices (see p. 24).

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TABLE 4Likelihood Rating of the Occurrence of Spawning of Rainbow Trout in Scotland

Place Source Rating Comments

Airthrey Loch M H Probably stream spawning, offspring seen onceBallo Reservoir M H Running water, limited successBrother Loch M H Sites not known, rare successNorth Third Reservoir A H Small fish near burn at Bluffs on south side in 1999Craufurdland Fishery M H Still water, first three years, Feb./April, no success notedDrummond Farm M H Running water, Dec./Jan., no successHeatheryford Fishery M H Still water, small fish reported each yearKingennie Fishery M H Running water inlets, Nov./Dec., no successKirkchrist Fishery M H Running water, Feb, one year before using triploidsCrakaig Estate Pond M H Fry in burn/lochDargarvel Loch M H Not known where, scale samples sent to FRS FLMill of Criggie Fishery M H Spring, running water, 1989/98Moffat Fishery M H Successful spawning each year, spring percolationLoganlea Reservoir A H Spawning in Logan BurnLinlithgow Loch A H Seen spawning in mouth of burn that enters Hatchery BayLoch Rusky A H Small fish notedGlensherup Reservoir A H Small fish noted, fine, clean gravel bedsOrchill Fishery M L Small fish notedWatch Reservoir A L Small fish notedColdingham A L Small fish notedPortmore A L Small fish notedLake of Menteith A L Small fish notedRiver Earn M L Small fish notedHowwood Fishery A L No other detailsButterstone Loch A L Small fish notedPortmore Reservoir A L Small fish notedUn-named loch M L Still present after stocking in 1993Loch Lochy A L Small fish notedStoneyfield Lochs A L Small fish notedBeecraigs A L Small fish notedLoch Awe A L Small fish notedRothiemurchus Fishery A L Small fish notedLoch Fad A L Small fish notedLoch Leven A L Small fish notedRiver Tay, Stanley A L Small fish notedDowally M H Spawning noted, still water, no successRotmell M H Spawning at edge regularly, no signs of successCorby Loch A L Small fish notedAuchintaple M H Small fish notedFincastle Loch M H Small fish notedLoch Bhac P.O. H Still water spawning, limited successDuntanlich Lochan P.O. H Offspring common, running water spawning, but died outLoch Fithie P.O. H Still water sites, offspring commonStraloch P.O. H Spawning occurred in still water, no success notedFL raceway P.O. H Spawning in running water, some successArdochy P.O. H Present for several decades, current status uncertainCrannoch P.O. H Small fish notedMonzievaird P.O. H Small fish notedLake of Menteith M H Reported by FRS FL Laboratory in early years of fisheryLoch Fad M H Reported by Phillipps et al., 1984

A = reported by anglerM = reported by fishery managerP.O. = personal observationsH = High likelihood that successful spawning occurredL = Low likelihood or requires confirmation

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2.5 Escaped Fish

Most of the replies referred to Scottish waters where rainbow trout have been found without having been stocked deliberately. These can be described loosely as ‘escapes’, although often their origins are uncertain. Some came from fish farms, whereas others may have moved away from waters that were stocked for angling. Table 5 lists 54 rivers or streams, seven freshwater lochs and three sea lochs or estuaries where rainbow trout were reported as escaped fish. Although this does not necessarily mean that escaped rainbow trout are there, currently in many instances, this is the case. Among the places reported are larger rivers like the River Tay or Tweed that could more properly be described as catchments of several smaller rivers. On a catchment basis, the River Awe and Loch Awe were mentioned 37 times, followed by the River Earn and Loch Earn (25 times), the River Tweed and tributaries (23 times) and the River Tay and Loch Tay (19 times). Once again, many of the waters were cited only once, so it is likely that several were missed. Loch Awe was the most frequently mentioned site (33 times). All of the areas where ‘escaped’ rainbow trout were commonly found are close to large fish farms from which large numbers of fish have been known to be lost from time to time, or there may be a relatively constant ‘seepage’ of farmed fish to the wild. There is now a legal requirement for fish farmers to notify the Scottish Executive of any incidences of escapes. There were no reports of rainbow trout escapes in 2001.

Some respondents mentioned numbers of rainbow trout ascending rivers from the sea and FRS FL staff confirm that several examples of this behaviour have been observed over the years. The numbers of so-called ‘steelhead’ appear to be very low, other than in circumstances when large escape incidents have occurred from marine cage sites and fish have soon afterwards entered local rivers. Few rainbow trout occurred in coastal and estuarine netting catches of salmon and sea trout that used to be sampled routinely by the FRS FL as part of its stock monitoring commitments.

2.6 Ecological Effects of Escapes

Several replies expressed concerns over the possible ecological effects of escaped rainbow trout on native salmonids, including from predation, competition for food, transfer of diseases and parasites and replacement by breeding success. Following these comments, the River Earn System is being investigated as a case study. Rainbow trout were reported to be common in the upper River Earn and Loch Earn and found regularly further downriver.

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TABLE 5The Numbers of Cited Occurrences of Escaped Rainbow Trout in Scottish Waters Based on the

Questionnaire

Place No Place No Combined Citations No

Loch Awe 33 River White Cart 1 Water of Ken 1

River Earn 14 River Bladnoch 1 Loch and River Awe 37

River Tay 12 Border Esk 1 Loch and River Earn 25

Loch Earn 11 River Borgie 1 Tweed plus tributaries 23

River Tweed 11 River Don 1 Loch and River Tay 19

Loch Lochy 6 River Doon 1

Loch Tay 5 River Eden 1

River Teith 5 River Ericht 1

River Awe 4 Loch Etive 1

River Gala 4 River Girvan 1

River Spey 4 River Halladale 1

River Annan 3 Loch Hope 1

River Dee (Abd) 3 River Isla 1

River Ettrick 3 River Kelvin 1

River Whiteadder 3 Kilbirnie Loch 1

River Allan 2 Kyle of Tongue 1

River Avon 2 River Laxford 1

River Cairn 2 River Leven (Fife) 1

River Devon 2 River Leven (Argyll) 1

River Lochy 2 Loch Linnhe 1

River Nith 2 Logan Burn 1

River South Esk 2 River Naver 1

Water of Leith 2 River North Esk 1

River Yarrow 2 River Orchy 1

River Allendar 1 River Ore 1

Alvie Burn 1 River Polla 1

Loch Arkaig 1 Polnoon W (upper ) 1

River Ayr 1 River at Kilmelfort 1

Bannock Burn 1 River Ythan 1

River Barr 1 River Tummel 1

Biel or Belton Burn 1 River Tyne 1

nb. These reported occurrences are spread over several years and do not necessarily reflect the current situation.

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3.1 Stocked Waters

As a result of her survey of the rainbow trout in Britain and Ireland carried out in the early 1970s, Frost (1974) found over 500 waters where there were records of the species, and 491 where they were confirmed as being present. Ninety-four of the latter waters were in Scotland. So far, the current survey has found about 300 Scottish sites that are stocked with rainbow trout, almost all being still waters. However, even this figure is an underestimate because many of the commercial put-and-take fisheries comprise several ponds, or lochs, listed under the same name. In addition some are likely to have been missed and an unknown number of private fisheries may not have been reported. It is impractical to obtain a complete list of stocked waters (not only for rainbow trout) within the scope of the current fishery legislation in this country. This is a matter for concern in relation to monitoring the status of inland fisheries and the fish stocks that support them, and in any planning and implementation of national strategic objectives for fishery management and conservation.

Based on the current survey, however, the number of Scottish waters stocked with rainbow trout has increased substantially, although the geographic distribution of the fisheries (Fig. 1) may be quite similar to that found by Frost (1974). Rainbow trout fisheries still tend to be situated within easy range of the more populated areas of the country and are much scarcer in the Highlands and Islands, where game fishing for wild fish is often much more readily available to both local anglers and visitors. The expense of regular transportation of large live fish from fish farms is likely to be an important limiting factor. Most of the rainbow trout fisheries seem to be targeting local and home-based, rather than tourist, anglers. In contrast, several fisheries are operated in conjunction with fish farms that are open to the public, for instance near Aviemore, Comrie and Glendevon. The fisheries that operate in conjunction with open fish farms cater for a greater proportion of tourist anglers.

3.2 Stocking Practices

Not only has the number of stocked waters increased, but the stocking levels have intensified since the early 1970s. In her study of rainbow trout in Britain and Ireland, Frost (1974) gave information of stocking levels in 25 still waters. She noted that ‘large fish’ of 10-12 inch (250–305 mm) were preferred. In the current Scottish survey, 68 fisheries supplied information on stocking densities. Almost all of these fisheries stocked with larger fish than the preferred size in the early 1970s. Sixty per cent of the fisheries stocked mainly with fish weighing 700-900 g (ca 350-400 mm). However, many of the smaller waters, in particular, receive a proportion at a specimen size. In their monthly reviews of Scottish put-and-take fisheries, the angling press commonly report the capture of rainbow trout weighing well upwards of 5 kg and fish of more than 10 kg are caught each year. Several large fish of this calibre were reported as escapes in lochs where there are cage farms. Most of these fish may have made much of their growth living in the vicinity of the cages, probably eating excess pellets that pass through the meshes.

3. Discussion

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According to Frost (1974), the general tendency in the early 1970s was for stocking with up to 100 fish per acre (247/ha). The density quoted appears to be the annual rate rather than the instantaneous rate of stocking. Since then, the trend has been for most commercial fisheries throughout the UK to stock several, or many, batches of fish per year. Alternatively, they will ‘trickle stock’ on a regular or daily basis, in order to obtain more even catch levels. Less frequent stocking tends to result in a ‘boom and bust’ situation that is highly favourable to the anglers who fish soon after stocking, but causes resentment at the leaner times. In the Scottish survey, 12 commercial fisheries reportedly stocked at annual rates in excess of 1,000 fish/ha, the maximum being 6,000 fish/ha. However, waters larger than about 5 ha tended to be stocked at progressively lower rates. Pawson (1982) also reported lower stocking densities in larger waters than in smaller put-and-take fisheries in the UK.

3.3 Spawning Success

The current survey continues to indicate that few rainbow trout spawn effectively in the wild in this country, as noted previously by Worthington (1940/41), Frost (1974) and Maitland and Campbell (1992). Frost (1974) found that self-sustaining populations only occurred at five localities. These were in the inflow streams at Blagdon Reservoir, near Bristol, the River Wye and one of its tributaries (the River Lathkill), in Derbyshire, a tributary of the Leigh Brook, near the Worcestershire/Herefordshire border; also, Lough Shure, Arranmore Island, in Co. Donegal and Lough na Leibe, near Ballymote, Co. Sligo, in the Republic of Ireland. It is unclear to what extent each of these formerly self-sustaining populations of wild rainbow trout is now supported by stocking, or by the presence of local fish farming. For example, spawning of fin-perfect and apparently wild rainbow trout still occurs each year on the River Wye, but a fish farm based above the area where spawning occurs uses trout from commercial sources (pers comm. W. Slaney). Compromising of the original population by fish farm stocking has also taken place at Lough Shure. Lough Shure is exceptional in that it is a moorland, peaty lough, seepage-fed, with strongly acid water chemistry (pH 4.8). The other self-sustaining populations were in calcareous waters based on limestone. Lough Shure was originally stocked in 1905 and no other introductions had occurred (Frost, 1974). Rather disappointingly, restocking has taken place with unrelated fish from mainland sources, as I discovered on a visit in 1994. Apparently, the original population was thought to have died out, so more were stocked. The cause of the loss of the naturalised spawning population is unknown. The water chemistry may have become even more acidic, although it is likely to have been buffered to an extent by sea spray. However, it is also possible that spawning sites were damaged, or made inaccessible, by the relatively recent construction of a low dam to increase its water reservoir holding capacity.

Maitland and Campbell (1992) refer to "about six" self-maintaining populations of rainbow trout, presumably including the five above that were described by Frost (1974). The sixth one, which was "probably self-propagating" in a hill lochan in Inverness-shire, is the one described earlier in this report as "Ardochy hill loch." Background information indicates that this was indeed a long-standing population, dating back to the beginning of the 20th Century. The suggestion made recently that rainbow trout still occur there warrants further investigation.

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In addition, there are likely to be many places where limited successful reproduction has occurred, without reaching the levels required for population maintenance. In most of these waters, restocking continues to take place, so the naturally-produced fish are likely to be absorbed within the wider population and may not be noticed or reported. Fish that escape at a small body size from land-based or floating fish farms further confuse the picture, since many of these are fin-perfect specimens that look as though they were natural spawned.

As was clearly confirmed by our own observations, rainbow trout can spawn successfully in Scottish waters. Of course, the current widespread use of ‘all-female’ and triploids further limits the opportunity for successful spawning. Previously, mixed-sex stocking was the norm, but even then the incidence of self-maintaining populations was not much greater than it is now. The presence of a few maturing male fish at fisheries which in recent years have stocked only with declared all-female or triploids could be due to their accidental inclusion from the suppliers. For example, the generation of triploidy in trout eggs tends not to be fully effective and small numbers of diploids may remain. These fish will continue to mature. Also, any successful spawning that occurred in the fishery prior to the introduction of single sex and triploid stocks could have led to some survivors of both sexes reaching maturity and spawning successfully again.

3.4 Reasons for Poor Spawning Success

Given an adequacy of both sexes, what limits the reproductive success of rainbow trout in the wild in the British Isles is unclear. Our climate is temperate and the highly varied hydrographic and geological conditions of our river systems and lochs fall within the range that the species must encounter within its home range in western North America. Rainbow trout are easily bred here in captivity. Almost all of the waters in Scotland where there is evidence of successful spawning are of neutral, or alkaline, water chemistry. However, that may simply reflect the fact that most waters that are selected for stocking with rainbow trout tend to be chemically and biologically richer ones, where the food supply is likely to be more adequate to maintain them. In contrast, the long-term survival of rainbow trout in the very acid water of Lough Shure in Ireland suggests that poor survival at low pH is not the sole answer to the mystery of their widespread lack of spawning success in Britain and Ireland. Frost (1974) concluded that the major problem was probably predation from and competition with native brown trout. Lever (1977) and Maitland and Campbell (1992) also thought that the newly emerged fry of rainbow trout would be at a competitive disadvantage compared with brown trout fry that tend to hatch earlier, since rainbow trout usually spawn later than brown trout. In addition, domesticated rainbow trout that are commonly used for stocking are likely to be behaviourly incompetent and have a reduced life when at liberty, compared to wild fish (Berejikian et al., 1996). Experimental studies suggest that the reproductive behaviour and reproductive performance of hatchery reared fish is impaired, especially as a result of domestication and selection for fish farming production traits (Fleming and Gross, 1992; Fleming et al., 1996; Youngson and Verspoor, 1998).

Taking a global view of rainbow trout, on the other hand, Fausch et al. (2001) found that their level of success in colonising new habitats was best explained by a match between fry emergence and months of low flood probability. Winter flooding and summer low flows favoured spring spawning

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and late emergence of rainbow trout. Spring or summer flooding at the time of fry emergence limited their chances of survival. Faush et al. (2001) also suggested that the low invasion success of rainbow trout in Europe could be due to low water temperatures hampering reproduction, mortality due to whirling disease parasites (Myxobolus cerebralis) and biotic interactions with brown trout. As discussed earlier, it would be surprising if low water temperatures limit rainbow trout spawning in Scotland because of our equable, oceanic climate. Our climate is so variable that ‘good’ years for spawning success in rivers must have occurred from time to time, i.e. low flows at the appropriate period in spring, and yet there has been no sign of pulses of survival of rainbow trout in the wild. However, it should not be forgotten that rainbow trout also spawn in still waters, where the environmental conditions experienced by the incubating eggs and emerging fry are likely to be more stable. Indeed, most observations of spawning success of rainbow trout in the UK are associated with still water springs and groundwater-fed rivers. Whirling disease is uncommon here (pers. comm. D. Bruno) and therefore cannot be considered a likely factor. This leaves biotic interactions with brown trout. Difficulties due to the normally sympatric occurrence of brown trout could be very important as their fry would normally emerge earlier in the year than those of rainbow trout and may take up the available feeding and resting territories.

Most likely, the problem for rainbow trout reproduction in the wild in these islands is a complex interaction of more than one factor. Viewed in the context of conserving our native stocks of fish, the colonisation of our waters by rainbow trout through natural reproduction is clearly not a high priority issue at present. However, with gradually changing climatic conditions, it is conceivable that the species could become naturalised here more successfully in the future.

3.5 Ecological Impacts

In the meantime, the survey has shown that some worries still exist about other ecological impacts of rainbow trout on native salmonid species, notably among District Salmon Fishery Boards. The widespread occurrence of escapes and the belief that their addition may exceed the carrying capacity of rivers and lochs and impact negatively on the production of juvenile salmon and trout continues to be a source of concern. These fears are not without foundation, for rainbow trout are active and aggressive feeders that have similar dietary habits to other salmonids. In this country, they grow more rapidly and tend to be easier to catch than brown trout, probably because they are less cautious (Maitland and Campbell, 1992). Scientific studies conducted in Scottish lochs tend to indicate some degree of habitat and resource partitioning between rainbow trout and brown trout, which would help to reduce the extent of their competition for food and space (Duncan, 1991; 1994). However, the extent of the interaction between these species is likely to vary among lochs of different physical and biological characteristics, and will depend also on the relative levels of abundance of the fish populations. There may be more likelihood of interaction in smaller lochs than in larger ones. A common finding in smaller natural lochs that are intensively stocked with rainbow trout is that angling catches of co-occurring brown trout are reduced. The perception is that the wild fish become scarcer, although there may be no direct evidence of predation. There are also concerns about the ecological effects of rainbow trout in Scottish rivers. Over the years, FRS FL has received a number of anecdotal accounts of rainbow

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trout in rivers eating salmon fry and parr. Examples include the Rivers Earn and Tay and the Aray, in Argyllshire. Predation by rainbow trout which are often larger than the resident wild fish is hardly surprising. However, the level of incidence of their predation upon native salmonids and its longer-term effects, if any, on the population size of the wild fish are unknown.

3.6 Diseases and Parasites

Finally, there are concerns about the introduction of diseases and parasites to native fish species as a result of the farming, stocking and escapes of rainbow trout and other fish species. Theoretically, most infections are likely to travel in the opposite direction, i.e. from wild to cultivated species, since the latter live a protected existence, eating processed food and are available for vaccination and medication when required. However, there is the risk that new diseases, or their variants, to which the local fish are not genetically adapted may be transferred between waters as a consequence of cultivating fish in high densities and then transporting them alive around the country. In the early 1970s, infectious pancreatic necrosis (IPN) caused serious mortalities in farmed trout in Scotland and England. However, after an infected farm on Loch Awe ceased operation in 1976, the virus was not found in many hundreds of wild fish sampled in the vicinity of the farm, or elsewhere within the loch, suggesting that it was rapidly lost from the system (Munro, 1988). Nevertheless, the potential remains for new potent diseases to be introduced and then spread among wild fish communities. The concern about parasites also applies to batches of wild fish that are moved around. It is evident from the rainbow trout survey that a considerable amount of moving and stocking of fish takes place into and within Scotland that is not readily traceable.

3.7 Demand for Rainbow Trout Fisheries

Whether the upward trend in stocking inland waters with ready-grown rainbow trout will continue may depend on several factors, including potential oversupply and competition among the fisheries and the relative popularity of angling for wild species. Many game anglers say they would rather fish natural waters, but they turn to stocked rainbow trout as an alternative when wild fish are scarce. However, that is not the full picture. A strong case can be made for the continued stocking of rainbow trout for a leisure industry that may still be growing in economic and recreational importance. The supported fisheries are easily accessible, they provide car parking, toilets, often sales of tackle and food, and are places where anglers can socialise. Many are attractively maintained and well-stocked with large fish. In addition, coaching can be arranged and advice is freely given on the currently successful flies and techniques. Anglers of all ages and both genders are catered for and welcome and often there are facilities for the disabled. Not many wild fisheries can claim to offer as much.

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3.8 Benefits to Predators

Furthermore, rainbow trout offer additional feeding opportunities for avian and other predators. The much-heralded and appreciated restoration of the osprey (Pandion haliaetus (L.)) to our common native fauna that has taken place in recent decades owes much of its success to the widespread stocking of rainbow trout. Ospreys are an important asset for tourism.

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4. Conclusions

Originally introduced from North America in the late 19th Century, the rainbow trout is now a common member of the inland fish community in Scotland that occurs in hundreds of lochs and many rivers. However, the species seldom spawns successfully in the wild in this country and its numbers are supported by aquaculture. Fish farms produce large tonnages for the table market and to supply an economically and socially important recreational sport fishery, based on put-and-take stocking. Artificially stocked rainbow trout help to maintain the diversity and abundance of avian and other predators. Concerns remain about the possible negative biotic impact of the species, including the ecological effects of escapes into waters where their presence is unintended.

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5. References

Anon. 2001. Scottish Fish Farms: Annual Production Survey, 2000. Fisheries Research Services, Marine Laboratory, Aberdeen, AB11 9DB. (ISSN : 1363-5859).

Berejikian, B.A., Mathews, S.B. and Quinn, T.P. 1996. Effects of hatchery and wild ancestry and rearing environments on the development of agonistic behavior in steelhead trout (Oncorhynchus mykiss) fry. Can. J. Fish. Aquat. Sci., 53, 2004-2014.

Duncan, W. 1991. An assessment of the current status of the fish communities in Loch Awe, Scotland: with particular reference to the interaction between feral rainbow trout Oncorhynchus mykiss Walbaum and indigenous brown trout Salmo trutta L.. Unpublished PhD thesis, University of Stirling.

Duncan, W. 1994. The fish community in Loch Leven. Hutchinson, P. and Walker, A.F. (eds). The Loch Leven Trout Fishery - Its Future. Institute of Fisheries Management Conference. pp. 29-38.

Fausch, K.D., Taniguchi, Y., Nakano, S., Grossman, G.D. and Townsend, C.R. 2001. Flood disturbance re-gimes influence rainbow trout invasion success among holarctic regions. Ecological Applications, 11(5), 1438-1455.

Fleming, I.A. and Gross, M.R. 1992. Reproductive behaviour of hatchery and wild coho salmon (Oncorhyn-chus kisutch): does it differ? Aquaculture, 103, 101-121.

Fleming, I.A., Jonsson, B., Gross, M.R. and Lamberg, A. 1996. An experimental study of the reproductive behaviour and success of farmed and wild Atlantic salmon (Salmo salar). J. Appl. Ecol., 33, 893-905.

Frost, W.E. 1974. A survey of the rainbow trout (Salmo gairdneri) in Britain and Ireland. Salm. Trout Assoc., London, 36pp.

Lever, C. 1977. The naturalized animals of the British Isles. Hutchison, London, 600pp.

Maitland, P.S. and Campbell, R.N. 1992. Freshwater Fishes of the British Isles. New Naturalist Series, Harper Collins, London, 368pp.

MacCrimmon, H.R. 1971. World distribution of rainbow trout (Salmo gairdneri). J. Fish. Res. Bd. Can. 28, 663-704.

Munro, A.L.S. 1988. Infectious pancreatic necrosis (IPN). Aquaculture Information Series, No 2, Marine Laboratory, Aberdeen. (ISSN 0953-2781).

Pawson, M.G. 1982. Recapture rates of trout in a “put and take” fishery: analysis and management impli-cations. Fish. Mgmt., 13(1), 19-31.

Phillips, M.J., Meikle, G.H., Beveridge, M.C.M. and Stewart, J.A. 1984. Rainbow trout and brown trout in Loch Fad and its tributary, Woodend Burn, Isle of Bute. Glasg. Nat., 20 part 5, 383-387.

Stuart, T.A. 1968/71. Studies on the Lake of Menteith. Dir. Fish. Res. Rep., pp.132-4 (1969), 114-15 (1971).

Worthington, E.B. 1940-41. Rainbows: a report on attempts to acclimatize rainbow trout in Britain. Salm. Trout Mag., 100, 241-261 and 101, 62-98. Youngson, A.F. and Verspoor, E. 1998. Interactions between wild and introduced Atlantic salmon (Salmo salar). Can. J. Fish. Aquat. Sci., 55 (Sup. 1): 153-160.

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AppendicesCase Histories of Rainbow Trout Reproduction in Scotland

A. Reported in Replies to the Questionnaire Glencorse/Loganlea ReservoirsDuring the 1990s, rainbow trout were seen spawning in the Logan Burn that runs between two reservoirs, Glencorse and Loganlea, which lie in the Pentland Hills, to the south-east of Edinburgh. Juveniles have been caught by anglers in both reservoirs and were confirmed in the connecting burn as recently as 2001. Fin-perfect rainbows, of a smaller size than normally stocked, are still caught occasionally (pers. comm. A. Christie).

Heatheryford FisheryThis is a put-and-take fishery (ca 4 ha) that lies beside the A9 road, close to Kinross which was opened 16 years ago. Each year, small rainbow trout are caught that are believed to have been naturally spawned. However, as undersized fish are returned alive, most are unreported (pers. comm. J. Cairns).

Mill of Criggie FisheryIn 1989, the rainbow trout fishery at Mill of Criggie, near St Cyrus, Kincardineshire, was extended to include a small inflow stream. Gravel was placed in this stream for the purpose of creating experimental redds which were planted with eyed ova. Fry resulted and naturally grown-on fish began to spawn there from winter 1992 until winter 1998, when the redds were intentionally destroyed. The perfect fin conformation of the spawners suggested that all were ‘wild’ fish returning to spawn in the same place (pers. comm. E. McVicar). Photographs of presumed naturally spawned fish were provided.

Moffat FisheryThe fishery comprises two spring-fed, purpose-dug lakes (ca 0.4 and 2 ha), situated near Moffat, Dumfriess-shire. Every year, rainbow trout spawn successfully in the vicinity of springs, although fewer fish are seen spawning now compared with earlier years of the fishery. The spawners include survivors from natural spawning, although there are also occasional mature fish among the triploids that are now used for stocking. Brook charr (Salvelinus fontinalis Mitch.) spawn successfully at the same fishery (pers. comm. S. Ottewell).

Plate 1:A recently spent female rainbow trout, believed itself to be of wild origin, from Rossdhu pond, Luss, Loch Lomondside (17 May 2002) ca. 300 mm

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Rossdhu Pond This is a small private fishery (ca 1 ha) on a golf course near Luss, Loch Lomond, which is restricted to members. The pond was excavated about 10 years ago. Each March/April since the first batches of the stocked fish matured, rainbow trout have spawned around the gravel shores, particularly near a small pipe that discharges water to the pond near the south-east end and naturally-spawned juveniles are common. It is believed that the mature males are mainly from natural spawning because recent stockings have been with triploids, although a few fish among these batches have matured. Less spawning activity has been noticed this year (pers. comm. J. Cronnie), but a recently-spent female and several other fin-perfect fish of about 300 mm in length were caught during a brief angling visit that I made on 17 May (Plate I). Stoneyfield LochsThis fishery comprises three lakes of about 5.5 ha in total area, near Invergordon, in Easter Ross. According to reports from the management and anglers, rainbow trout spawn there every year and juveniles are common. This is another fishery where brook charr also spawn successfully (pers. comm. J. Connell).

B. Previously known to the FRS Freshwater Laboratory

Ardochy Hill LochIn 1974, FRS FL was informed about a long-standing population of rainbow trout in a small hill loch(1.2 ha) situated above Loch Loyne in Inverness-shire. The loch lies on at an elevation of 440 m in a moorland area that has since been partly afforested. Rainbow trout were believed locally to have been stocked about 50 years earlier, prior to which time it was said to be fishless. The story was verified by the late Donald MacPherson of Invermoriston who had first-hand knowledge of the stocking. At first, the rainbow trout grew well, the largest reaching 5 lbs (ca 2,300 g), but then they became over-abundant for the available food supply and declined in size. In 1974, after an absence of twenty years, Mr MacPherson returned to fish the loch and caught two weighing about three quarters of a pound (340 g). We visited the loch on 21 May 1975 and eventually caught a single rainbow trout in a gillnet, indicating that the population was precarious, but confirming at least that the species identification was correct. The netted specimen was a fin-perfect, three-year-old male (265 mm; 210 g) that had not fully recovered from spawning. A weedy bog lochan further upstream appeared to be fishless. No fish were seen in the small inflow and outflow streams adjacent to the main loch. Based on the rocky moorland habitat surrounding the loch, it might have been expected to be more acidic than the water sample indicated at the time (pH 6.8 and alkalinity of 1.1, equivalent to mgl total hardness of CaCo3), indicating moderate buffering capacity, although the pH would be expected to fall during periods of heavy rainfall. Several years later, enquiries made with the estate owner suggested that the rainbow trout population had died out. Last year, however, there was an unconfirmed report that rainbows were still present and a visit is planned to investigate whether a recovery of the original population has occurred.

Corby LochCorby Loch was recently reported to us as a possible site of successful spawning of rainbow trout. The following notes are extracted from an e-mail sent by Ron Tourney:

“It is about 30+ acres (>12ha) in extent and quite shallow (usually 1-2m deep). It lies immediately NE of Aberdeen on a Site of Special Scientific Importance. I am informed that it was created in the 30’s by damming the burn which powered Mundurno Mill, so as to provide adequate water for the mill during the summer months. This burn still feeds and drains the loch, the outlet is fitted with a grid to prevent fish escapes. The inlet burn drains the Red Moss area and as a consequence the water is extremely peaty, though I have never measured the pH. In the winter months there are often 3,000+ wild geese roosting on the loch so there may be some fertilisation from this source. The bottom is mostly deposited peat with stony margins, but there are areas of 3 - 5 mm gravel, particularly around the outlet bay. The loch seems to support good invertebrate life. The present management of Corby took over about ten years ago and is responsible for

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its development as a fishery. The original stocking was with brown trout which grew on very well and certainly bred. The brown trout caught in Corby now are the offspring of the original stocking. Over the past three seasons the loch has received about 400 triploids per annum, generally at about 2 lbs weight. Non-triploid rainbows were stocked up until four years ago. The fish seem to grow on well and one of more than 10 lbs was caught this year. A great deal of the loch is sanctuary. I have been told that the rainbows from the non-triploid stocking had bred. I actually did not believe this and assumed the small ones referred to were accidental additions via routine stocking, I never actually saw any of these fish myself until this season. This year I heard of some rainbows of 4-5 lbs caught in late April-May that were full of large eggs. In July/August of this year there were reports of increased numbers of smaller rainbows, from 3-4 oz up to more than 2 lb in weight described as fin perfect and of a very silvery appearance and with a pale pink line. I caught one myself two weeks ago, which I returned. This fish was about 1 1/2 lb and as described, very silvery and with perfect fins, absolutely no sign of damage or repair - a very beautiful fish.” Crakaig PondThis is a small pond (less than 0.5 ha) near Loth in Sutherland that was stocked with rainbow trout in conjunction with the operation of a caravan site during the late 1980s. Small numbers of rainbow trout fry were confirmed by electro-fishing in summer 1993 in a partially covered field drain running into the pond (pers. comm. M. Donaghy).

Loch BhacThis is a hill loch (ca 12 ha), surrounded by coniferous forestry, that lies to the north of Loch Tummel, in Perthshire. It is managed by the Pitlochry Angling Club, and has been stocked with rainbow trout, and occasionally brook charr, on a put-and-take basis, since 1975. It also contains a natural population of small brown trout. Typically of the area around Pitlochry, Loch Bhac lies on intrusions of metamorphic limestone, therefore its water chemistry is mildly calcareous. In the early years of the rainbow trout stocking, mixed sex fish were used, some of which survived to maturity. Spawning took place in March/April on an area of gravel, partially covered with fine silt, that used to be the entry point for the main inflow stream. The cutting activity of the trout created circular cleared patches. Occasional, fully-finned juveniles were caught, but none have been reported in recent years, when the stocking policy has been to use ‘all-females’. The stocked fish in the early batches were individually handled and there is no possibility that fry were introduced accidentally at that time, therefore there was evidence of limited success in reproduction of rainbow trout in Loch Bhac. The same was true of several other lochs in the area at that time.

Duntanlich LochanThis is an unnamed, very small (less than 1 ha), shallow (less than 1.5 metre deep) artificial lochan, fed by two small hill streams which lies in the hills to the south of Loch Tummel. In 1975, the owner treated with the piscicide rotenone to remove an over-abundant population of brown trout and stocked it with 35 brook charr and 22 rainbow trout, all aged 1+ years. All of this was supervised by FRS Freshwater Laboratory. The brook charr quickly became firmly established through natural spawning. Juveniles and adults were present in the streams above and below the lochan and are still present throughout the catchment, although now threatened by a recent stocking of brown trout. Some of the rainbow trout also spawned successfully and a 150 mm specimen, aged one year, was sampled as late as 10 May 1981, six years after the original fish were stocked. After a further light stocking of rainbow trout in 1984, 10 aged 0+ (120-145 mm) were sampled by electro-fishing in the outflow burn on 22 October 1986. A further five immature rainbow trout (262-275 mm) were caught by angling in the lochan on 10 September 1987. None are known to have been caught there in recent years. Both the brook charr and the rainbow trout spawned successfully but, whereas the brook trout established a self-sustaining population, the rainbow trout failed to do so. It is interesting to speculate on the outcome if the rainbow trout had been stocked on their own. Competitive interactions between the two exotic species could have favoured the brook charr. However, the recently added brown trout seem to be ousting even the brook charr. Based on a visit last autumn, juvenile brown trout are now by far the more common species throughout the outflow burn. The lochan contained a mixed population of brown trout and mainly older brook charr, suggesting that the brook charr may now be suffering from a lack of juvenile recruitment.

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Loch FadSuccessful spawning of rainbow trout has been documented in Loch Fad, on the Isle of Bute, where a commercial cage farm has been located since 1976. In September and December 1981, rainbow trout fry (0+ years) that were found by electro-fishing in its main tributary, the Woodend Burn, were smaller than any held at the fish farm at that time, indicating that rainbow trout had spawned successfully in the burn. Ripe male and female rainbow trout, identifiably from fish farm stock, were captured there during repeat visits during November 1981 and March 1983. Woodend Burn is fast-flowing and has extensive gravel areas. It has a mean pH of 6.9 and mean total hardness of 33 mgl-1 as CaCO3 (Phillips et al., 1984).

Loch FithyIn the early 1970s, visits were made to Loch Fithy, a flooded gravel pit (ca 18 ha) near Forfar, to investigate reports of rainbow trout spawning successfully. At that time, the loch was used as a private fishery and, each year, some potential brood stock fish were harvested by a fish farmer, using large box traps (ca 2 m square by 1.5 m high), with wire mesh leaders to the shore. This was a technique that we later used to good effect in a stocking trial at Straloch (see below). During late winter/early spring, rainbows clearly could be seen spawning on shelving banks of gravel. Some fry survived because there were many smaller rainbow trout in the loch than the minimum size that had been stocked (pers. comm. S. Tur). However, no research was carried out to assess the levels of survival over time.

Monzievaird LochThis private loch (ca 20 ha) which lies in light deciduous woodland close to Crieff, in Perthshire, still holds a self-maintaining population of brook charr that were originally introduced in about 1890 (Lever, 1977). In 1965, the loch was treated with rotenone to remove coarse fish and, at that time, some of the brook charr were removed and later replaced, in order to preserve the breeding population, which is still extant (pers. comm. S. Brown). Subsequently, rainbow trout were stocked for a few years. During an exploratory gill-netting visit to inspect the brook charr made in November 1976, 17 small rainbow trout (160-210 mm) were sampled which the owner stated were from natural spawning (pers. comm. R. Carrington-Smith). Since then, stocking with rainbow trout has been discontinued, and their current status in the loch is unknown.

Freshwater Laboratory pondsDuring the early 1970s, some mixed sex rainbow trout were held in concrete ponds at the FRS Freshwater Laboratory, in conjunction with the stocking experiment at Loch Straloch, which is described below. The ponds were supplied with water that was pumped to a head tank from Loch Faskally and discharged via a pipe into a short concrete raceway (ca 10 metre long by 1.5 metre wide) that fed the ponds. In December 1974, two year-old mature fish began to show heightened activity associated with impending spawning, males were highly aggressive to each other and coveted females. Some females were artificially stripped and the eggs fertilised and held in a hatchery, where they eventually hatched. High levels of survival (ca 90%) were recorded. In early January 1975, mixed gravel was placed in the concrete raceway to see whether the remaining ripe fish would use it for spawning. However, colder weather set in until early February and made the fish torpid. With the onset of milder conditions and a small increase in water temperature, extensive spawning began to take place in the raceway. This was allowed to take place until mid-February when screens were put in place to keep the remaining fish in the ponds. Unfortunately, there were two major failures of the pumps that supplied water to the head tank and the gravel raceway was dewatered. However, in spite of drying and overnight freezing of the gravel, some of the buried ova survived and fry began to emerge and commence to feed in early May. Twenty-four that were sampled during the next few days were transferred to the hatchery where they readily adapted to a commercial diet. Clearly, the spawning and incubation conditions in the raceway were well short of optimal, yet some success was achieved.

StralochBeginning in May 1973, a stocking experiment was carried out to examine the spawning biology of rainbow trout in the wild. At that time, it was clear from anecdotal information and our own observations that the species was managing to reproduce to a small extent in a number of local waters. Put-and-take stocking

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with takeable fish was beginning to become popular with Scottish anglers, encouraged by the angling press. Two hundred and fifty 2 year-old rainbow trout were obtained from a hatchery at Almondbank and released into Straloch, a small (9 ha), artificial and biologically productive, private loch near Pitlochry that contains a natural population of brown trout. The loch is shallow (less than 2 metres deep) and the outflow over a dam is barred to retain larger fish. Most of the brown trout spawn in two small inflow streams that enter the loch from the opposite shore from the dam. A pipe from the nearby Brerachan Burn, the headwaters of the River Ardle, can be opened to top up the water level. Occasionally, unusually large salmon parr and smolts (more than 300 mm in length) are caught by anglers, having found their way in through the pipe and then been confined to the loch.

Some of the brown trout at Straloch were believed to spawn in still water (pers. comm. R. Thorburn), so it was thought possible that the rainbow trout might use the same sites. In order to sample them, box traps with chicken mesh leaders from the shore, were installed in two areas where the loch bed comprised gravel, mostly with a fine covering of silt. One of the sites was along the shelving shores of a promontory, the other in a shallow area about 30 m from the bank. A third box trap was set at the mouth of the larger of the two inflow streams. During October–early December 1973, all of the traps caught large numbers of mature brown trout and kelts. The still water traps also caught mature ‘landlocked’ salmon, including two ripe females (295 mm and 305 mm). It was confirmed through repeated direct observation that some of the brown trout did indeed spawn on the gravel patches within the loch. However, the traps had to be removed for several weeks from late December to late January 1974, due to freezing of the loch. With the onset of milder weather in early February, ripe male rainbow trout began to appear regularly in the still water traps. All of these fish were released bearing individually numbered tags to avoid double counting. The first ripe female was sampled at the end of February and two female kelts were taken on 28 March. By mid-April, rainbow trout were clearly seen spawning in the same still water gravel areas that had been used by the brown trout. By then, the rainbow trout were aware of the leaders and traps and actively avoided them, therefore the catches gave a poor indication of the numbers of mature fish that were using the sites. Spawning activity ceased by the end of the month. In all, 28 mature rainbow trout, comprising 19 males, six ripe females and three female kelts were sampled. Four immature fish also were captured. Surprisingly, no mature rainbow trout were caught in the upstream trap. During the next two seasons, only an occasional naturally-spawned fish was reported from the angling catches. No further stocking with rainbow trout was carried out and the species soon disappeared from the loch which was allowed to revert to a brown trout fishery.

Lake of MenteithThe Lake of Menteith, a large loch (263 ha) lying to the west of Stirling, at the edge of the Trossachs, which contains several coarse fish species and small numbers of wild brown trout, has been operated as a rainbow trout fishery since 1967. In the early period of the trout fishery, a former colleague of the Laboratory, the late Tom Stuart, reported successful spawning of rainbow trout in the Malling and Portend Burns (Stuart, 1968/71). Subsequently, hatchery operations compromised detailed observations of the levels of spawning success. No successful spawning has been seen there for many years, although large numbers of rainbow trout continue to be stocked. In recent years the fish have been ‘all-females’ (pers. comm. Q. Glen).