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

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<ul><li><p>Hydrobiologia 290: 91-102, 1994.K. J. Murphy, M. C. M. Beveridge &amp; R. Tippett (eds), The Ecology of Loch Lomond. 91g 1994. Kluwer Academic Publishers. Printed in Belgium</p><p>The fish community of Loch Lomond, Scotland: its history and rapidlychanging status</p><p>Colin E. AdamsFish Behaviour and Ecology Group, University Field Station, Rowardennan, Glasgow G63 OAW, UK</p><p>Key words: Loch Lomond, fish community, introductions</p><p>Abstract</p><p>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.</p><p>Introduction</p><p>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.</p><p>The biological, conservation and recreationalimportance of the Loch</p><p>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</p><p>nutrient rich, warmer south in general tending to favourmore specialised species, such as the cyprinids.</p><p>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.</p><p>Loch Lomond also has nationally important popu-lations of particular species (Lyle &amp; 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 &amp; 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.</p></li><li><p>92</p><p>% 706050</p><p>%70760 ~ Inverbeg Bank50 N = 21040302010</p><p>0 VI</p><p>0 C0. a En </p><p>u e hMo</p><p>%706050403020100</p><p>Auchentullich BaN - 319</p><p>a) C) 0 X5</p><p>U))0o 0~</p><p>Co, a P~0 0F. r.,M</p><p>River EndrickN = 220</p><p>., N[-]n nn A d !z</p><p>a)0</p><p>40302010</p><p>3 ) -P -0~~~~~~~A 0 0'd -5 , J~Ida~~~~~~~~~~~~~mo</p><p>0 0 0 X ; 00 00 . HR '0 d0 0 % 0P 0 P :</p><p>W .. . V </p><p>00) o 0040300N91 W.4) . , U i; 00 0 a 50 a)</p><p>J o * c X =@O </p><p>E N Sn</p><p>Mu a.</p><p>'</p><p>a)II0.a1.</p><p>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.</p><p>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-</p><p>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</p><p>Falloch MouthN = 267</p><p>osgain= 265</p><p>41</p></li><li><p>93</p><p>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).</p><p>The structure of the fish community</p><p>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.</p><p>Historic accounts of the fish community pre-1970.</p><p>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.</p><p>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).</p><p>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-</p><p>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 &amp; Tippett,1990), it is most likely that this record did result froma mis-identification.</p><p>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 &amp;Brown (1901), eventually died out.</p><p>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.</p><p>Thick-lipped mullet (Crenimugil labrosus) wasrecorded in the River Leven by Lumsden &amp; Brown(1895) and by Scott &amp; 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.</p><p>The record of plaice (Pleuronectes platessa) inLoch Lomond by Scott &amp; 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).</p><p>The fish community post-1970</p><p>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.</p></li><li><p>94</p><p>Table 1. Records of fish species from Loch Lomond</p><p>Species</p><p>Sea lampreyRiver lampreyBrook lampreySalmonSea/Brown troutRainbow trout</p><p>Arctic charr</p><p>Brook charr</p><p>PowanPikeCrucian carp</p><p>Gudgeon</p><p>Tench</p><p>MinnowRoachChub</p><p>Dace</p><p>Stone loachEelThree-spined sticklebackTen-spined sticklebackEurasian perchRuffe</p><p>FlounderThick-lipped mullet</p><p>Plaice</p><p>Petromyzon marinusLampetrafluviatilisLampetra planeriSalmo salarSalmo truttaOncorhynchus mykiss</p><p>Salvelinus alpinus</p><p>Salvelinus Jontinalis</p><p>Coregonus lavaretusEsox luciusCarassius carassius</p><p>Gobio gobio</p><p>Tinca tinca</p><p>Phoxinus phoxinusRutilus rutilusLeuciscus cephalus</p><p>Leuciscus leuciscus</p><p>Noemacheilus barbatulusAnguilla anguillaGasterosteus aculeatusPungitius pungitiusPercafluviatilisGymnocephalus cernuus</p><p>Platichthys fiesusCrenimugil labrosus</p><p>Pleuronectes platessa</p><p>Status</p><p>NativeNativeNativeNativeNativeOccurring regularly in catchment (Lamond 1931;Maitland 1966) presence probably only maintained by farm escapees.2 historic records (Ure 1795; Bidie 1896) neitherconfirmedIntroduced c. 1876 (Brown 1896) but failed tobecome established and died outNativeNativeIntroduced - first recorded 1991 (Adams &amp; Mitchell1992) establishment success not yet knownIntroduced - established by early 1980's (Maitlandetal. 1983)Introduced - (Young 1870; Lumsden &amp; Brown 1895)but failed to become established and died out -norecords from the 20th century.NativeNativeIntroduced - established by mid 1980's (Adamsetal., 1990)Introduced - established by mid 1980's (Adamset al., 1990)NativeNativeNativeNativeNativeIntroduced - established by mid 1980's (Maitlandet al., 1983; Maitland &amp; East 1989).Nativepreviously recorded only in River Leven (Lumsden &amp;Brown 1895; Scott &amp; Brown 1901) but personalrecollections of R. McMath, University Field Stationof mullet of unknown species from gill nets in mainloch in early 1970's.a record of this species in Loch Lomond by Scott &amp;Brown (1901) is highly dubious not normallyregarded as a freshwater species</p><p>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</p><p>it had been deliberately introduced (Maitland et al.,1983).</p><p>This record was followed in 1982 by the discoveryof another fish species new to Loch Lomond, the ruffe</p></li><li><p>95</p><p>(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).</p><p>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.</p><p>In 1991 one further species not native to the catch-ment, crucian carp (Carassius carassius) was discov-ered there, (Adams &amp; Mitchell, 1992) as with the othernew species, crucian carp is native to more southerlyparts of the UK.</p><p>Vector of introductions</p><p>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.</p><p>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).</p><p>The current status of fish community</p><p>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 &amp; Tippett, 1990).</p><p>Powan</p><p>nder</p><p>e</p><p>iceRuffe</p><p>fU oucnTrout</p><p>Fig. 2. Catch composition of gill net captures (all sites combined)corrected for catch-perunit-effort. Exploded segments - introducedfish species.</p><p>Loch captures</p><p>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.</p><p>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).</p><p>River captures</p><p>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, howev...</p></li></ul>