Hydrobiologia 290: 91-102, 1994.K. J. Murphy, M. C. M. Beveridge & R. Tippett (eds), The Ecology of Loch Lomond. 91g 1994. Kluwer Academic Publishers. Printed in Belgium

The fish community of Loch Lomond, Scotland: its history and rapidlychanging status

Colin E. AdamsFish Behaviour and Ecology Group, University Field Station, Rowardennan, Glasgow G63 OAW, UK

Key words: Loch Lomond, fish community, introductions

Abstract

The fish community of Loch Lomond is of national importance. Its diversity of species and rare populations of powan(Coregonus lavaretus) and freshwater feeding river lampreys (Lampetrafiuviatilis) warrant high conservation status.It is also of value for its sport fisheries for sea-trout (Salmo trutta), salmon (Salmo salar) and pike (Esox lucius).Historical records demonstrate that the species composition of the fish community has remained stable over avery long period until recently when a series of introductions of fish species new to the catchment has resulted insuccessful colonisation by a number of species. These have resulted in fundamental changes in the ecosystem. Hereusing historical records the long-term stability of the fish community is examined, recent rapid changes in the fishcommunity are documented and some of the resultant effects of changes in the fish community are demonstrated.

Introduction

The assemblage of species that makes up the fishcommunity of Loch Lomond, Scotland, is unique, ofnational importance and under threat. In this paper Iexplore the basis for this claim by reviewing the histor-ical literature, by providing a description of the currentstatus of the fish community and by describing recentchanges that have occurred and some of their conse-quences.

The biological, conservation and recreationalimportance of the Loch

The importance of the Loch Lomond fish communitylies partly in its relative diversity of species. Maitland(1972) lists the 15 species of fish known to occur in theloch and its tributaries at that time. This is more thanfor any other Scottish loch. This richness of species ispartly a result of the dichotomous nature of the loch(see Tippett, (1994) for a full description). The condi-tions in the narrow, deep, oligotrophic highland northof the catchment generally favouring the adaptable,phenotypically plastic, generalist species, such as thesalmonids, and the conditions in the shallower, more

nutrient rich, warmer south in general tending to favourmore specialised species, such as the cyprinids.

In reality of course, the Loch Lomond catchmentis more complex than this and offers a multiplicity ofaquatic habitats ranging from invertebrate poor, torren-tial streams to nutrient rich ox-bow lakes. The resultis that this wide range of habitats plus the loch's closelink with the sea (the River Leven draining the systeminto the Clyde estuary, is only 13 km long) providesuitable environments for a wide range of fish species.

Loch Lomond also has nationally important popu-lations of particular species (Lyle & Maitland 1992).The powan (Coregonus lavaretus) population is proba-bly the largest of only two populations in Scotland andonly seven in the UK and since 1986 has been affordedprotection under Schedule 5 of the Wildlife and Coun-tryside Act 1981 (see Brown & Scott (1994)). LochLomond's population of river lampreys (Lampetraflu-viatilis) is the only known population in the UK thatdoes not migrate to sea but remains in freshwater (seeMaitland et al. (1994)) probably feeding mainly onpowan (Robertson, 1870). The roach (Rutilus rutilus)population is also interesting in that a proportion of thepopulation undertakes a spawning migration each yearup the River Endrick, the main tributary in the southof the catchment, to breed.

92

% 706050

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00) o 0040300N91 W.4) . , U i; 00 0 a 50 a)

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a1.

Fig. 1. Catches of fish (percentage catch-per-unit-effort) from five littoral sites in Loch Lomond and gill and seine net and electro-fishingcatches in the River Endrick between November 1988 and October 1989.

Loch Lomond also supports an important sport fish-ery for Atlantic salmon (Salmo salar) and sea-trout(Salmo trutta) which as been managed since at least1860. The Loch Lomond Angling Improvement Asso-ciation is the angling association that currently con-

trols the salmonid fishings in the vast majority ofthe catchment. The Association was formed in 1895and is thus one of the oldest fishing clubs in the UK(Lamond, 1931). It currently has around 900 membersand employs 5 full-time bailiffs. In recent years Loch

Falloch MouthN = 267

osgain= 265

41

93

Lomond has also become an important fishery for pike(Esox lucius) and in 1947 produced the current Scottishrod-caught record for this species weighing 21.6 kgs(47 lbs 11 oz).

The structure of the fish community

As a result of its importance as a sport fishery andmore recently because of scientific and conservationinterest, the fish fauna of Loch Lomond has been betterdocumented than any other major inland waterway inScotland. An examination of the literature shows thatthe fish community has undergone two distinct andcontrasting phases during its recorded history.

Historic accounts of the fish community pre-1970.

The first known full account of the fish fauna of LochLomond was in 1795 by Ure (1795), this was fol-lowed by accounts by Brown (1891), Lamond (1931)and Hunter et al. (1959). These accounts and oth-er records have been comprehensively reviewed byMaitland (1972). Although nomenclature differencesaccounted for most of the discrepancies between Mait-land's list of 15 species of fish occurring in LochLomond and previous fish fauna lists (see Table 1)there are some additional records that are worth exam-ining more closely.

Tench (Tinca tinca) have been recorded from theloch by several authors (Young, 1870; Brown, 1891;Regan, 1911) and a specimen was exhibited to theNatural History Society of Glasgow on the 19th ofDecember 1870. According to Lumsden and Brown(1895) this species was restricted to the area aroundthe mouth of the River Endrick. There have been norecords of this species during the 20th century and it isthought to have died out (Hunter et al., 1959; Maitland,1972). It is likely that extinction of this species inLoch Lomond was the result of a spawning failure asaccording to Wheeler (1969), tench only spawn whenthe water temperature reaches 18 C, it is unlikelythat this temperature would be consistantly achieved inLoch Lomond to enable successful spawning (Slack,1957).

Arctic charr (Salvelinus alpinus) was recorded fromLoch Lomond by Bidie (1896) and there is mention ofcharr in Loch Lomond in the Statistical Account ofScotland (Stewart, 1796). The 1896 record was reject-ed by naturalists at the time as a mis-identification pos-

sibly of a brook charr (Salvelinusfontinalis) (Brown,1896). As there have been no other records of thisspecies either before or since, despite considerablecollection effort (Maitland, 1972; Adams & Tippett,1990), it is most likely that this record did result froma mis-identification.

Brook charr are known to have been introducedto Loch Lomond around 1876 (Brown, 1896) andalthough the introduced stock maintained its identity,it did not become established and according to Scott &Brown (1901), eventually died out.

Several specimens of the Rainbow trout(Oncorhynchus mykiss) have been recorded from theRiver Endrick pre-1970 (Lamond, 1931; Maitland,1966a). Maitland (1966a) suggests that these all result-ed from cultured escapes from farms or artificiallystocked sites and that they are unlikely to becomeestablished in the catchment. More recently rainbowtrout have been consistently represented in rod-and-line captures by anglers (H. Ward pers. comm.), how-ever the condition factor and fin damage to these fishsuggest that they originate from fish farms, there is noevidence to suggest a self-sustaining population.

Thick-lipped mullet (Crenimugil labrosus) wasrecorded in the River Leven by Lumsden & Brown(1895) and by Scott & Brown (1901). The personalrecollections of R. McMath (University Field Station,Rowardennan) of mullet (of unknown species) caughtin moderate numbers in gill-nets set in Milarrochy Bayin the early 1970's represent the only known recordof mullet in the main loch and can not be lightly dis-missed. However because of the paucity of recordsof mullet in the main loch despite relatively intensivecollection over many years it seems that this speciesenters the main loch, at best infrequently.

The record of plaice (Pleuronectes platessa) inLoch Lomond by Scott & Brown (1901) is highly dubi-ous as there have been no other records of this speciesentering freshwater. It is possible that this record result-ed from confusion of this species with the relativelycommon flounder (Platichthysfiesus).

The fish community post-1970

The end of the 1970's marked a clear watershed forLoch Lomond, as the fish community entered a periodof rapid and dramatic change, unprecedented in itshistory, as five fish species, new to the Loch Lomondcatchment were recorded there.

94

Table 1. Records of fish species from Loch Lomond

Species

Sea lampreyRiver lamprey

Brook lampreySalmonSea/Brown trout

Rainbow trout

Arctic charr

Brook charr

Powan

Pike

Crucian carp

Gudgeon

Tench

Minnow

RoachChub

Dace

Stone loach

Eel

Three-spined stickleback

Ten-spined stickleback

Eurasian perch

Ruffe

Flounder

Thick-lipped mullet

Plaice

Petromyzon marinus

Lampetrafluviatilis

Lampetra planeri

Salmo salarSalmo trutta

Oncorhynchus mykiss

Salvelinus alpinus

Salvelinus Jontinalis

Coregonus lavaretusEsox luciusCarassius carassius

Gobio gobio

Tinca tinca

Phoxinus phoxinus

Rutilus rutilus

Leuciscus cephalus

Leuciscus leuciscus

Noemacheilus barbatulus

Anguilla anguilla

Gasterosteus aculeatus

Pungitius pungitius

Percafluviatilis

Gymnocephalus cernuus

Platichthys fiesus

Crenimugil labrosus

Pleuronectes platessa

Status

Native

Native

Native

NativeNative

Occurring regularly in catchment (Lamond 1931;

Maitland 1966) presence probably only maintained by farm escapees.2 historic records (Ure 1795; Bidie 1896) neither

confirmed

Introduced c. 1876 (Brown 1896) but failed to

become established and died out

NativeNative

Introduced - first recorded 1991 (Adams & Mitchell

1992) establishment success not yet known

Introduced - established by early 1980's (Maitland

etal. 1983)

Introduced - (Young 1870; Lumsden & Brown 1895)

but failed to become established and died out -no

records from the 20th century.

Native

Native

Introduced - established by mid 1980's (Adams

etal., 1990)

Introduced - established by mid 1980's (Adams

et al., 1990)

NativeNative

Native

Native

Native

Introduced - established by mid 1980's (Maitland

et al., 1983; Maitland & East 1989).

Native

previously recorded only in River Leven (Lumsden &Brown 1895; Scott & Brown 1901) but personal

recollections of R. McMath, University Field Station

of mullet of unknown species from gill nets in mainloch in early 1970's.

a record of this species in Loch Lomond by Scott &Brown (1901) is highly dubious not normally

regarded as a freshwater species

In 1981, a fish species new to the catchment, thegudgeon (Gobio gobio) was discovered in the RiverEndrick. This species apparently made its way into thesystem from a small loch in the catchment to which

it had been deliberately introduced (Maitland et al.,1983).

This record was followed in 1982 by the discoveryof another fish species new to Loch Lomond, the ruffe

95

(Gymnocephalus cernuus). This species had not beenrecorded in Scotland before this and was thus 250 kmoutwith its previously reported range in the UK (Mait-land et al., 1983).

In 1987 yet two more species new to the catch-ment, dace (Leuciscus leuciscus) and chub (Leuciscuscephalus) were found in the lower reaches of the Riv-er Endrick (Adams et al., 1990). Prior to this, bothspecies had a more southerly UK distribution.

In 1991 one further species not native to the catch-ment, crucian carp (Carassius carassius) was discov-ered there, (Adams & Mitchell, 1992) as with the othernew species, crucian carp is native to more southerlyparts of the UK.

Vector of introductions

Studies of isolated communities such as are found inisland ecosystems have shown that natural invasionsof isolated habitats resulting from dispersal of speciesis a relatively rare phenomenon (Roughgarden, 1986).For obligate freshwater fish species with poor powersof dispersal, Loch Lomond is an isolated ecosystem.However the rapid changes in the fish community com-position have not resulted from an unusual biologicalevent, rather they are almost certainly the result ofhuman activity.

Gudgeon are known to have been deliberately intro-duced into a pond in the catchment of the RiverEndrick, from where they made their way into theriver system (Maitland et al., 1983). The other fourspecies probably all emanate from the discarded live-bait of pike anglers collected from catchments in Eng-land and/or Wales (Carnell, 1987).

The current status of fish community

To assess any change in the fish community structure,following the introduction of these new fish species, awide ranging survey was undertaken between Novem-ber 1988 and October 1989. Over this period fish werecollected regularly by multipanel, gill net (19-50 mmmesh size) at 5 littoral zone sites from the extreme northto the extreme south of the main loch. Fish were alsocollected by gill net, seine net and by electro-fishingin the lower reaches of the River Endrick (Fig. 1) (forfull details of the survey see Adams & Tippett, 1990).

Powan

nder

e

ice

Ruffe

fU oucnTrout

Fig. 2. Catch composition of gill net captures (all sites combined)corrected for catch-perunit-effort. Exploded segments - introducedfish species.

Loch captures

Ten fish species were recorded in catches at the fiveloch sampling sites. Overall powan dominated catches(Fig. 2), making up 40% of all fish collected, howeverintroduced ruffe were also extremely common mak-ing up 24% of catches. Other fish species included incatches were: roach 15%; brown trout (Salmo trutta)- 6%; perch (Percafluviatilis) - 5%; Atlantic salmon -4%; pike - 3% and introduced dace - 3%. Eels (Angul-la angulla) and flounders made up less than 1% ofcatches.

Introduced ruffe were the most common species incatches at two of the five loch sites examined, secondmost common at Inverbeg Bank, and was ranked thirdmost common at the other two sites. Introduced dacewere only recorded at the two most southerly sites,(Ross Priory Bay and Auchentllllich Bay) (Fig. 1).

River captures

Figure 1 also shows the catch composition data for sitesin the lower reaches of the River Endrick. Becausethese data result from more than one collection tech-nique they are more comprehensive in their coverageof the species present, however as a result they are alsonot directly comparable with loch catches.

Fourteen species of fish were recorded in the low-er reaches of the River Endrick. Underyearling min-nows and roach dominated catches such that on severaloccasions they could not be counted. All four newlyintroduced species recorded by 1989 were found in thisarea. Ruffe made up 16% of catches, dace 28%, chub

96

2.3% and gudgeon 2.3% of all catches excluding roachand minnows.

The establishment of introduced species

Using the above data plus ad hoc records from othersources it is possible to build up a picture of the statusof introduced fish species by the end of 1989. By thistime it is clear that all 4 newly invaded species hadestablished sizable populations in the Loch Lomondcatchment.

By 1989 it would appear that chub, had notincreased their range in the catchment beyond the low-er reaches of the River Endrick. A waterfall, the Pottsof Gartness 18 km from the mouth of the river presentsan impassable barrier to further upstream expansion ofthe population for this species. There is, however, nobarrier preventing distribution downstream, yet to datethere have been no records of this species in the mainloch. There is some question of the long term viabilityof this species as according to Wheeler (1969) chub donot spawn until water temperatures reach 15 C. Thisis only acheived for a very short period in mid summer(Maitland, 1966b). Despite this, they are commonlycaught by coarse anglers in the River Endrick, whoregard this species as common there.

Gudgeon have also become well established in thelower reaches of the River Endrick below the Potts-of-Gartness, where they are relatively abundant in electro-fishing catches. This species has recently (1990-91)also moved into the main loch where it is commonlycaught in fyke traps set for eels in the Balmaha area.There are no records of this species from other locali-ties.

Dace would appear to have been more successfulin establishment than chub and gudgeon. When theywere first formally recorded in 1987, it was clear thatthey were abundant in the lower reaches of the RiverEndrick below the Potts-of-Gartness. However at thistime they were not established in some areas of theEndrick system accessible to them (the River Blane)nor had they been recorded in the main loch. Howeverin the following years, dace expanded their range in thecatchment. By 1989 ad hoc electro-fishing in the Blaneshowed that they were now resident there. In addition,by the end of 1989 dace were commonly collected ingill nets set throughout the south end of the main loch(Fig. 3). Since then dace have continued to extend theirrange in the main loch and have now been collected asfar north as Rowardennan (1991) (pers. obs.).

Of all the introduced species recorded, the one thathas shown the most spectacular powers of establish-ment has been the ruffe. Maitland & East (1989) havedemonstrated the remarkable population growth of thisspecies by monitoring the number of dead fish col-lected from trash screens at the Ross Priory PumpingStation on the south shore of Loch Lomond. The firstruffe were recorded there in 1982, in the years follow-ing this, the numbers rose exponentially (Maitland &East 1989). Data presented here (Fig. 1) shows thatthe dramatic ruffe population explosion occurring atRoss Priory was mirrored throughout the loch. Ruffeare now almost ubiquitous throughout the catchment,only excluded from areas such as the upper reaches oftributaries where they are prevented from invading byimpassable barriers and from tributaries with a highwater velocity, ruffe are poor swimmers.

There is every reason to suspect that the latestrecorded fish introduction, crucian carp, may also nowbe establishing itself. Electro-fishing at the site of itsfirst discovery showed that more than one year classwas present, according to Wheeler (1969) this speciesis capable of spawning at relatively low temperatures.

Thus, after a long period of stability lasting atleast 2 centuries and probably even longer, the fishcommunity, as a result of a series of introductions ofnew species, is now undergoing a period of instabil-ity unprecedented in its recorded history (Fig. 4). Inthe last comprehensive review of the fish communityof Loch Lomond, Maitland (1972) recorded 15 estab-lished fish species now, only two decades later, at least19 (and probably 20) species are established there, 35%of all British freshwater fish species (Maitland, 1977).

Factors affecting colonisation success in LochLomond

The colonisation of Loch Lomond by ruffe and to alesser extent by dace, described here, has clearly beenhighly successful. Ruffe have extended their rangethroughout the accessible parts of the catchment andits population size has increased explosively over thedecade since its arrival, such that it is now probably thecommonest species there. With the benefit of hindsightit is clear that ruffe is a highly successful coloniserspecies but it is important to consider why has ruffebeen such a successful coloniser, when others such astench and brook charr have not? What are the charac-teristics of ruffe that have enabled successful coloni-sation to occur? And are there any generalisations that

97

Fig. 3. Range expansion by dace between 1987 and 1989 in the Loch Lomond catchment.

22

20

18

16

14

120o o o

0' 0) )Fig. 4. Historical changes in species composition of the Loch Lomond fish community

Fig. 4. Historical changes in species composition of the Loch Lomond fish community.

can be made about the characteristics of successfullycolonising species?

Predicting which species are likely to be successfulcolonists following invasion has proved to be highlyunsuccessful in the past. It would appear that there isno one single biological characteristic distinguishing

those species that are successful colonists from thosethat are not (Moyle, 1986). However, some generalcharacteristics of successful invaders have been iden-tified, (Ehrlich, 1986; Moyle,1986) and it is interestingto see which of these characters might apply to ruffe.

0)

CD

Q)

.,

z0

98

According to Ehrlich (1986) and Moyle (1986) ingeneral, successful colonisers are likely to be:

1) Omnivorous - ruffe are extremely catholic in theirdiet, including a wide range of invertebrates, fishova and fish (Johnson, 1965; Adams & Tippett,1991).

2) Hardy - able to function in a wide range of envi-ronments - ruffe have a relatively high temperaturetolerance range with an upper lethal temperature of31 C (Varley, 1967) yet they can maintain foragingto temperatures as low as at least 4 C (Bergman,1987; Adams & Tippett, 1991).

3) Short generation time/high fecundity - the age atwhich 50% of individuals spawn in a stable ruffepopulation has been reported as 1 year old for malesand 2 years for females (Varley, 1967) - fecundityis relatively high (Muus & Dahlstrom, 1967).

4) Widely distributed in their original range - (seeWheeler, 1969)

5)Genetically heterogeneous - this is unknown forruffe.

6) Associated with humans - the translocation of ruffeto Loch Lomond was by man.

It is clear from the above that ruffe fit most ofthe criteria of a successful colonising species. Thusit is perhaps not surprising that ruffe have recentlybeen accidentally introduced to Lake Superior, NorthAmerica (Pratt et al., 1992; Selgeby & Ogle, 1991) andto Lake Constance (R. Rosch, pers. comm.) in bothlakes they are apparently colonising very successfully.

Successful colonisation however, is not solely afunction of the coloniser but also depends on thecommunity it is invading. Therefore it is importantto ask what characteristics of the invasion site haveenabled colonisation to occur. Several authors haveexamined the characteristics of communities that makethem suseptable to successful invasion. Orians (1986)states that invasion is more likely to be successful ifthe ecosystem is undergoing a period of disturbance.Evidence would suggest that Loch Lomond was notundergoing a period of disturbance during colonisationby ruffe although one could speculate that communitydisturbance caused by colonisation by ruffe may haveaided other invading species. Moyle (1986) has shownthat communities are likely to be more suseptable toinvasion by species from within the same country thanby exotic (non-endemic) species. All five non-nativespecies recently recorded in Loch Lomond fit into thiscategory. In addition Case (1990) has shown that the

probability of successful establishment of an invad-ing species increases with decreasing community sizeand with increasing average strength of competitionbetween species in the invaded community. Althoughthere is little known about the strength of competi-tion between native species in Loch Lomond, the fishcommunity, as a result of being further from sites ofdispersal of freshwater fish following the last ice age,is a relatively impoverished one, compared with com-munities further south.

Thus it would appear that, a priori ruffe wouldappear to be a potentially invasive species and that thefish community of Loch Lomond, as with most othersin Scotland, might be judged to be susceptible to inva-sion by new species. Thus if the identity of Scottish fishcommunities is to be maintained, protection from therisk of accidental introductions must be an importantconsideration.

The ecological impact of the introduction andcolonisation by new fish species

Given that now at least four new species have becomeestablished in Loch Lomond, it is important to estab-lish what changes in the ecosystem have resulted. Thepotential effects of the introduction of new fish specieson the existing fish species has been explored by Wel-comme (1986) who suggests 5 potential effects.

The concomitant introduction of new parasites ordiseaseBecause obligate freshwater fish communities are bytheir nature isolated from each other, they are alsobuffered from the effects of the transmission of diseasefrom one freshwater community to another. Thus theintroduction of fish obtained from outwith the catch-ment considerably increases the risk of also transmit-ting a parasite or disease to which that catchment hasnot yet been exposed.

This effect has been documented with the introduc-tion of a crustacean parasite Argulusfoliaceous alongwith dace into lakes in the English Lake District (Fry-er, 1982). This parasite is now also commonly foundon fish in Loch Lomond and has been found 'free liv-ing' in benthic samples (Adams, unpublished data; S.Rushton-Mellor pers. comm.) where it had not pre-viously been recorded (Cambell, 1971) however it isimpossible to determine with certainty if this parasitehas simply been overlooked in previous surveys of fish

99

parasites or whether it is an example of concomitantparasite introduction.

Hybridisation with or gene pool changes to nativespeciesIsolated fish populations may frequently show localadaptations to local environmental conditions, much ofthis adaptation may be genetically based. Introductionof fish of the same species with differing adaptationsmay result in genetic dilution of locally adaptive traits.In addition many related fish species will relativelyreadily hybridise. This is particularly prevalent in thecyprinids. On the 11 September 1989 a single spec-imen of a roach (Rutilus rutilus) X bream (Abramisbrama) hybrid was collected from Loch Lomond. Theorigin of this fish is uncertain, however one possibili-ty is that it is the first generation hybrid progeny of apreviously undetected population of bream and nativeroach (Adams & Maitland, 1991).

Competition with native fish speciesClearly introductions of competitively superior specieswith niches overlapping with existing native speciesmay exclude native species from resources that arein short supply such as food, feeding sites, spawningareas, etc.

Comparing the diet of dace with salmon parr showsthat the diet of these two species overlaps considerably.Mann (1974) examined the diet of dace in the RiverStour, and found 81% of the prey items (by number)were Ephemeroptera, Trichoptera and Diptera, com-pared with 82% for salmon parr from the River Endrick(Maitland, 1965). In addition dace and salmon parrappear to be occupying similar habitats in the Riv-er Endrick (Adams, unpublished data). This clearlypoints to potential competition for food between thesetwo species.

Environmental change to the ecosystemThis may occur when an introduced fish specieschanges the environment to the detriment of a nativespecies.

There is no evidence that this effect may be occur-ring in Loch Lomond.

Changes in the relationship between predator and preyThis effect is certainly the most widely reported effectresulting from the introduction of new fish species toinland waterways. The best known example is that ofthe deliberate introduction of Nile perch (Lates niloti-

Ruffe

Powan

Brown trout

Fig. 5. The proportion of powan ova in stomachs of each of thethree main fish predators.

100

% 80

60

40

20

0

100

80

60

40

20

0

100

80

60

40

20

0

Cormorants1 oon_

9

o .C . = C

Cr 0W 0 0Ir a

1989-90

c V .c

o 0 eXL n 0- n E

* 0 =t E

V} 0(K 0

Herons

1978

E_o o0 of a

1990

-. 0

Cr 0 it:Ofr

Fig. 6. The occurrence of fish prey in the diets of cormorants, pikeand herons, before and after the establishment of new fish species inLoch Lomond.

re 1

100

IIIII

*\I

I

Fig. 7. Interspecific predator/prey interactions that have become newly established (solid lines) or weekened (broken lines) as a result of theintroduction of ruffe to Loch Lomond.

cus) to Lake Victoria, East Africa, in 1960. This pis-civerous species quickly became established and rapid-ly devastated commercially important populations ofprey species such as the endemic haplochromines andthe tilapia, Oreochromis sp. driving these species toextinction in some areas (Barel et al., 1985).

When it was discovered that ruffe had been intro-duced to Loch Lomond, one potential repercussionof colonisation was quickly established. Pokrovskii(1961) demonstrated that ruffe were regulating the pop-ulation size of Coregonus albula, a close relative of thepowan, in Russian lakes by affecting spawning successthrough ova predation. To determine if a similar inter-action between ruffe and powan was occurring in Loch

Lomond, the diet of fish foraging on the powan spawn-ing grounds at the Ross Isles was examined during thespawning seasons 1988-90.

The results of this study showed that powan them-selves as well as native brown trout and introducedruffe were foraging on powan ova during the incuba-tion period following egg deposition (Adams & Tip-pett, 1991). However because unlike powan and browntrout, ruffe foraging activity is not curtailed by thelow water temperatures found at this time (5- 7 C)(Bergman, 1987; Adams & Tippett, 1991) ruffe intakeof ova was significantly greater than that of the otherpredators. Ruffe accounting for 64% of all observedova predation by fish (Fig. 5). Although we do not

101

know the ultimate effects of ruffe predation on ova,it is known that powan ova mortality rate from othersources is very high (see Slack, (1957); Brown & Scott(1994)) and there is a risk that increased mortality fromruffe predation of powan ova may seriously impact onthe powan population.

The relationship between powan and its predatorsis not the only predator-prey relationship to have beenaffected by new fish introductions. Between 1990 and1991 the diet of cormorants (Phalacrocorax carbo)feeding on Loch Lomond was monitored by regularexamination of regurgitated remains recovered at themain roosting site (Fig. 6). This data shows that anestimated 85% of the diet of this species is now ruffe(see Adams et al. (1994) ). Clearly ruffe representa large, abundant and available food source for cor-morants which did not exist before 1980.

One pisciverous species for which good data existon diet before recent introductions is pike. Shafi (1969)examined the diet of pike between 1955 and 1967.At this time pike were feeding principally on powan(57%). To look for a change in the feeding strategyfollowing changes in the fish community, I repeat-ed Shafi's study in 1989-90. The results (summarisedin Fig. 6) demonstrate a clear change in pike forag-ing strategy with a shift in their diet from principallypowan, a fast moving pelagic species, to ruffe, a poorswimming, benthic species (Adams, 1991).

One other fish eating species that has also changedits diet following new fish introductions, is the heron(Ardea cinerea). Giles (1981) examined the diet ofherons feeding at the Gartfairn heronry in the south-east corner of Loch Lomond in 1978. At this time,herons were principally feeding on roach (63%). Whenthe diet of herons at this colony was re-examined in1990 (Fig. 6) it was found that they had shifted thereprey choice to primarily ruffe (61%).

It is clear that the introduction of new fish species(principally ruffe) has had major repercussions for thelong-term, well established, predator-prey relation-ships that have been in existence for several centuries.Figure 7 sumarises those predator/prey relationshipsthat are known to have altered, it is clear that theremay be many more interspecific interactions betweenpredator/prey; host/parasite; resource competitors, thatare also likely to have changed.

I have shown here that Loch Lomond is currentlyin a phase of rapid flux, resulting from the introduc-tion and successful colonisation of the loch by at leastfour fish species new to the catchment. It will takemany years for all the repercussions for the ecosys-

tem of these introductions to become clear howev-er data sumarized here shows that the effects alreadyquantified are far-reaching, extending throughout theecosystem, and fundamental, changing the basic long-established relationships between species.

Acknowledgments

The new work described here could not have beenachieved without the assistance and support of DavidBrown. Thanks to Roger Tippett, Rab McMath andnumerous other volunteers who gave freely of theirtime and advice. Much of the data presented here wascollected with support from Scottish Natural Heritage.

References

Adams, C. E., 1991. Shift in pike, Esox lucius L., predation pressurefollowing the introduction of ruffe, Gymnocephalus cernuus (L.)to Loch Lomond. J. Fish Biol. 38: 663-667.

Adams, C. E., D. W. Brown & L. Keay, 1994. Elevated predationrisk associated with inshore migrations of fish in a large lake,Loch Lomond, Scotland. Hydrobiologia 290: 135-138.

Adams, C. E., D. W. Brown & R. Tippett, 1990. Dace (Leuciscusleuciscus (L.)) and chub (L. cephalus (L.)) new introductions toLoch Lomond. Glasg. Nat. 21: 509-513.

Adams, C. E. & P. S. Maitland, 1991. Evidence of further invasionsof Loch Lomond by non-native fish species with the discoveryof a roach X bream, Rutilus rutilus (L.) X Abramis brama (L.),hybrid. J. Fish Biol. 38: 961-963.

Adams, C. E. & J. Mitchell, 1992. Introduction of another non-nativefish species to Loch Lomond: Crucian carp (Carassius carassius(L.)). Glasg. Nat. 22: 165-168.

Adams, C. E. & R. Tippett, 1990. The status of the fish community.Report to the Nature Conservancy Council, Hope Terr., Edin-burgh, 29 pp.

Adams, C. E. & R. Tippett, 1991. Powan, Coregonus lavaretus(L.) ova predation by newly introduced rufre, Gymnocephaluscernuus (L.), in Loch Lomond, Scotland. Aqua. Fish. Mgmnt22: 239-246.

Barel, C. D. N., R. Dorit, P. H. Greenwood, G. Fryer, N. Hughes,P. B. N. Jackson, H. Kawanabe, R. H. Lowe-McConnel, M.Nayoshi, A. J. Ribbink, E. Trexavas, F. Witte & K. Yamaoka,1985. Destruction of fisheries in Africas lakes. Nature 315: 19-20.

Bergman, 1987. Temperature dependent differences in foraging abil-ity of 2 percids, Percafluviatilis (L.) and Gymnocephalus cernu-us. Envirn. Biol. Fish 19: 45-53.

Bidie, G., 1896. Char in Loch Lomond. Ann. Scot. Nat. Hist. p 258.Brown, A., 1891. The fishes of Loch Lomond and its tributaries.

Scot. Nat. 10: 114-124.Brown, A., 1896. Char in Loch Lomond. Ann. Scot. Nat. Hist. p

192.Brown, E. A. R. & D. B. Scott, 1994. Life histories of the powan,

Coregonus lavaretus (L.) (Salmonidae, Coregoninae) of LochLomond and Loch Eck. Hydrobiologia 290: 121-133.

102

Cambell, A. D., 1971. The occurrence of Argulus (Crustacea:Branchiura) in Scotland. J. Fish Biol. 3: 145-146.

Carnell, D., 1987. Pike baits have fled the loch. Anglers Mail, 3rdOctober 1987.

Case, T. J., 1990. Invasion resistance arises in strongly interactingspecies-rich model competition communities. Proc. Natl. Acad.Sci. 87: 9610-9614.

Ehrlich, P. R., 1986. Which animals will invade? In The Ecologyof Biological Invasions of North America and Hawaii (H. A.Mooney & J. A. Drake, eds) Ecological Studies 58, SpringerVerlag, New York.

Fryer, G., 1982. The parasitic copedoda and branchiura of Britishfreshwater fishes. F B. A. Publication No. 46, Freshwaler Bio-logical Association, Windermere.

Giles, N., 1981. Summer diet of the grey heron. Scott. Birds 1: 153-159.

Hunter, W. R., M. D. Slack, & M. R. Hunter, 1959. The lowervertebrates of the Loch Lomond district. Glas. Nat. 18: 84-90.

Lamond, M., 1931. Loch Lomond. Jackson, Glasgow, pp. 340.Johnson, P., 1965. Studies on the distribution and food of ruffe (Ace-

rina cernua) in Denmark with notes on other aspects. DanmarksFiskeri-og Huvundersogelser 4: 137-156.

Lumsden, J. & A. Brown, 1895. A guide to the natural history ofLoch Lomond and neighbourhood. Bryce, Glasgow, 103 pp.

Lyle, A. & P. S. Maitland, 1992. Conservation of freshwater fish inthe British Isles: the status of fish in National Nature Reserves.Aquatic Conservation: Marine and Freshwater Ecosystems 2:19-34.

Maitland, P. S., 1965. The feeding relationships of salmon, trout,minnows, stone loach and three-spined-stickleback in the RiverEndrick, Scotland. J. Anim. Ecol. 34: 109-153.

Maitland, P. S., 1966a. Rainbow trout, Salmo irideus Gibbons, inthe Loch Lomond district. Glasg. Nat. 18: 421-423.

Maitland, P. S., 1966b. Studies on Loch Lomond II - the fauna ofthe River Endrick. Blackie, Glasgow. 194 pp.

Maitland, P. S., 1972. Loch Lomond: Man's effects on the salmonidcommunity. J. Fish. Res. Bd Can. 29: 849-860.

Maitland, P. S., 1977. A coded checklist of animals living in fresh-water in the British Isles. ITE, Edinburgh. 76 pp.

Maitland, P. S. & K. East, 1989. An increase in the numbers of ruffeCymnocephalus cernua (L.) in a Scottish loch from 1982 to 1987.Aqua. Fish. Mgmnt 20: 227-228.

Maitland, P. S., K. East & K. H. Morris, 1983. Ruffe, Gymnocephaluscernua (L.) new to Scotland in Loch Lomond. Scott. Nat. 7-9.

Maitland, P. S., K. H. Morris & K. East, 1994. The ecology of lam-preys (Petromyronidae) in the Loch Lomond area. Hydrobiologia290: 105-120.

Mann, R. H. K., 1974. Observations on the age, growth, reproductionand food of dace Leuciscus leuciscus (L.) in two rivers in southernEngland. J. Fish Biol. 6: 237-253.

Moyle, P. B., 1986. Fish introductions into North America: Patternsand ecological impact.ln The Ecology of Biological Invasions ofNorth America and Hawaii (Mooney, H. A. & Drake, J. A. eds)Ecological Studies 58, Springer-Verlag, New York.

Muus, B. J. & P. Dahlstrom, 1967. Freshwater fish of Britain andEurope. Collins, London. 148 pp.

Orians, G. H., 1986. Site characteristics favouring invasion. In TheEcology of Biological Invasions of North America and Hawaii(Mooney, H. A. & Drake, J. A. eds) Ecological Studies 58,Springer-Verlag, New York.

Pratt, D. M., W. H. Blust & J. Selgeby, 1992. Ruffe, Gymnocephaluscernuus: newly introduced in North America. Can. J. Fish. Aquat.Sci. 49: 1616-1618.

Pokrovski, V. V., 1961. Basic environmental factors determining theabundance of whitefish. Trudy Soveshchanii, 13: 228-234.

Regan, C. T., 1911. British Freshwater Fishes, Methuen, London.Robertson, D., 1870. On Petromyzon fluviarilis and its mode of

preying on Coregonus clupeoides. Proc. Nat. Hist. Soc. Glasg.2: 61-63.

Roughgarden, J., 1986. Predicting invasions and rates of spread. p179-188. In The Ecology of Biological Invasions of North Amer-ica and Hawaii (Mooney, H. A. & Drake, J. A. eds) EcologicalStudies 58, Springer-Verlag, New York.

Scott, T. & A. Brown, 1901. The marine and freshwater fishes. In Thefauna, flora and geology of the clyde area (Elliot, G. F., Laurie,M. & Murdoch, J. B., eds) Brit. Assoc. Adv. Sci., Glasgow.

Selgeby, J. H. & D. H. Ogle, 1991. Status of ruffe in Lake Superior.Report to the Great Lakes Fishery Commission, March 1991.

Shafi, M., 1969. Comparative studies of populations of perch (Percafluvialilis) and pike (Esox lucius) in two Scottish lochs. Ph.D.thesis, University of Glasgow, 143 pp.

Slack, H. D., 1957. Studies on Loch Lomond -1. Blackie, Glasgow.133 pp.

Stewart, J., 1796. Parish of Luss. Statistical Account of Scotland17: 238-271.

Tippett, R., 1994. An introduction to Loch Lomond. Hydrobiologia290: xi-xv.

Ure, D., 1795. Parish of Killearn. Stast. Acc. Scot. 16: 100-129.Varley, M. E., 1967. British freshwater fishes -factors affecting their

distribution. Fishing News Books, London, 148 pp.Welcomme, R. L., 1986. International measures for the control of

introductions of aquatic organisims. Fisheries 1: 4-9.Wheeler, A., 1969. The fishes of the British Isles and North-west

Europe. Macmillan, London, 613 pp.Young, J., 1870. Tench from Loch Lomond. Proc. Nat. Hist. Soc.

Glasg. 2: 67.