Ecology and conservation of arctic charr, Salvelinus alpinus (L.), in Loch Doon, an acidifying loch in Southwest Scotland

Biological Conservation 55 (1991) 167-197

Ecology and Conservation of Arctic Charr, Salvelinus alpinus (L.), in Loch Doon, an Acidifying Loch in Southwest Scotland Peter S. Maitland Fish Conservation Centre, Easter Cringate, Stirling FK7 9QX, UK

Linda May, David H. Jones Institute of Freshwater Ecology, Penicuik EH26 0QB, UK

& C. Ross Doughty Clyde River Purification Board, East Kilbride G75 0LA, UK

(Received 2 February 1990; revised version received 12 May 1990; accepted 29 May 1990)

ABSTRACT Several populations of arctic charr Salvelinus alpinus in southern Scotland have become extinct and Loeh Doon is the only site left for the species in the southwest. The catchment o f the Ioch lies mainly on granite and much has recently been afforested. Most o f the inflowing streams are acid and the loch itself appears to have acidified over the last two decades. Few acid-sensitive invertebrates occur in the streams or in the loch. The fish populations of the most acid streams are low in density. Growth o f arctic charr in the loch resembles that in some other Scottish loehs but appears to have increased in recent years. The charr feed on benthic invertebrates for much o f the year but on zooplankton in the summer. Spawning occurs in early October, leaving the fish in poor condition which improves during the spring to reach a maximum in late summer, just prior to spawning. Spawning takes place over gravel and stones in shallow water all round the loch. 167 BioL Conserv. 0006-3207/90/$03"50 © 1990 Elsevier Science Publishers Ltd, England. Printed in Great Britain

168

Peter S. Maitland, Linda May, David H. Jones, C. Ross Doughty Angling data indicate that the average size of both trout and arctic chart in Loch Doon has increased significantly over the last 15 years. Chemical and biological evidence suggests that Loch Doon is acidifying and that management is necessary if the stock of charr there is to be saved.

INTRODUCTION In the British Isles, most populations of arctic charr Salvelinus alpinus (L.) (Morton, 1955) have been isolated from each other for thousands of years in individual lakes, and during this time they have developed a variety of phenotypic characteristics (Gunther, 1865; Day, 1887; Regan, 1909, 1914) which are probably genetically based (Nyman, 1972; Child, 1977, 1984; Ferguson, 1981). The phenotypic differences between some populations are so great that many of them were originally described as distinct species. A number of populations of arctic charr have disappeared in various countries, including Ireland (Avondhu, 1951), England and Scotland (Maitland et al., 1984). All the Scottish losses appear to have been in the south--Loch Leven, St Mary's Loch, Loch Grannoch and Loch Dungeon-and Loch Doon is the only remaining site for the arctic charr in southwest Scotland. The nearest surviving populations of this species are found in Cumbria, England, and in the southwest highlands of Scotland (notably Loch Eck and Loch Lubnaig). Recently, Partington and Mills (1988) have shown that Loch Doon charr are clearly distinct from English and Welsh charr on meristic grounds, for in the Loch Doon fish both the mean numbers of gill rakers on the first gill arch and the number of branchiostegal rays are substantially lower than in British populations further south. The objective of the present research was to study the present status of arctic charr in Loch Doon and to determine the extent of any threats, especially acidification, to its continued existence there. Other fish present in Loch Doon (note: nomenclature for fish and invertebrates throughout this paper follows Maitland (1977)) are occasional Atlantic salmon Salmo salar, brown trout Salmo trutta, minnow Phoxinus phoxinus, stone loach Noemacheilus barbatulus, eel Anguilla anguilla and perch Perca fluviatilis.

LOCH DOON Loch Doon (Fig. 1) is a large oligotrophic lake which has been designated by the Nature Conservancy Council as a Site of Special Scientific Interest mainly for its population of arctic charr. There has been serious acidification of several lochs nearby and Loch Doon may become more acid in the near

Arctic charr in southwest Scotland

169

$4

L7

N

Loch Doon L3

•

:

~i ~

s~ 1 1kin I

I

/ Fig. 1. Outline map of Loch Doon and its catchment, showing the main sampling sites On Loch Doon (L1-L7) and on the major tributaries: Gala Lane (SI, S1A), Carrick Lane ($2), Garpel Burn ($3) and the River Doon ($4), the outflow from the loch. Also indicated are four of the larger lochs in the catchment: Loch Enoch (a), Loch Macaterick (b), Loch Riecawr (c) and Loch Finlas (d).

future. Acidification is almost certainly the reason that charr have disappeared from Lochs G r a n n o c h and D u n g e o n nearby. Loch Enoch, a former trout fishery in the headwaters of the D o o n catchment, has become acidified and completely fishless in recent years (Maitland et ai., 1987). Trout populations in at least two other waters (Lochs Riecawr and Macaterick) in the D o o n catchment are also significantly affected by acidification (Hay, 1984). Although the major source waters of Loch D o o n are highly acidic and apparently toxic to fish well before it enters the sea, the natural outflow, the River D o o n , is a well-buffered and useful salmon water. The bedrock o f the

170

Peter S. Maitland, Linda May, David H. Jones, C. Ross Doughty

Loch Doon catchment is extensively base-poor granite but to the north there are considerable areas of rocks (e.g. Ordovician shales) which are richer in bases. A few areas have been limed. About 35% of the catchment is afforested and more is proposed. The valley occupied by Loch Doon (Fig. l) runs roughly north and south. The axis of the loch basin itself is strongly curved but overall the loch is narrow and elongate--some 9 k m in length and 2.4km at its greatest breadth. The mean breadth is 0-5 km. The maximum depth, about 2.4 km from the head of the loch, was originally about 30-5 m and the mean depth was 8-2 m (Murray & Pullar, 1910). The superficial area of the natural loch at the beginning of the century was 5"2 km 2 and the total volume 43 million m 3. The area drained naturally was 131 km 2 and included many smaller lochs (e.g. Riecawr, Macaterick, Finlas, Muck, Derclach, Enoch, etc.). The outflow by the River Doon to the north (now controlled by a dam) is through a rocky channel. The surface was some 205.2 m above sea level when surveyed by Murray and Pullar (1910). In order fully to understand the ecology of Loch Doon, it is important to appreciate the complexities imposed by t h e Galloway Hydro-Electric Scheme (at present operated by the South of Scotland Electricity Board) which was begun in 1931 and completed in 1936. Loch Doon forms the principal storage for various power stations as well as the storage required for maintaining the compensation flow to its previous single outflow--the River Doon (this flow is supposed to average 205 million litres per day). The loch was raised to a new level by the construction of a concrete dam 17.7 m in height and 169 m long across the original outlet. A new outlet channel was formed to the south of the previous outlet. The loch now has an available total storage capacity of 82"1 million m 3 with a draw-down of 12-2 m. The area of the loch at the new spillway level (215 m above sea level) is 9.11 km 2 (South of Scotland Electricity Board, 1984).

METHODS

Chemistry Monthly measurements of pH in the River Doon below Loch Doon have been made by the Clyde River Purification Board since 1975. More recently (1986-88) additional samples were taken quarterly from the inflowing streams and the outflow (Fig. 1). These were collected in 1-1itre acid-washed polypropylene bottles; separate 250-ml samples were collected for pH and alkalinity determinations. Samples were analysed, using standard methods, for pH, calcium, magnesium, sodium, potassium, aluminium (total filtrable),

Arctic charr in southwest Scotland

171

alkalinity, sulphate, chloride and conductivity. Samples from the loch (Fig. 1) were taken monthly during this period and analysed for some of the above determinands and also for phosphate and nitrate. Invertebrates Long-term data on benthic invertebrates in the outflow from Loch Doon are available from the records of the former Ayrshire River Purification Board and the present Clyde River Purification Board. Sampling frequency varied from one to three times a year. In recent years (1986-88), benthic invertebrate samples have been taken twice yearly (spring and late summer) in the major inflows and the outflow at the same sites at which water samples were collected (Fig. 1). Three-minute samples were taken with a rectangular handnet with a 1-mm mesh using a kick technique (Standing Committee of Analysts, 1979). Samples of benthic invertebrates were collected with the same net from the stony littoral of the loch at six sites during 1986 (Fig. 1 and Table 4). Handnet samples were taken in April, June, August and November using a 3-min kick-sweep technique followed by a 1-min hand washing of stones into the mouth of the net. Samples of zooplankton were collected using vertical net hauls from the open waters of the loch on three occasions in 1987. Crustacea were sampled with a plankton net of 40 meshes/cm and Rotifera with a net of 200 meshes/ cm.

All samples were fixed and subsequently sorted and identified using standard methods. Fish One of the problems in studying rare or potentially endangered fish is how to sample them without harming the population (Maitland, 1974). At Loch Doon, it was known that arctic chart were still present in some numbers, but sampling was kept to the minimum consistent with obtaining samples which would give some valid information on the ecology of the fish there and allow the removal of reasonable numbers of eggs for conservation management purposes. Charr were sampled on four occasions during 1986-87 by standard mixed-mesh survey gill nets, with mesh sizes of 19-120 mm. These nets were always fished on the bottom of the loch, usually in the profundal area of the southern basin, but also in the littoral area during the spawning season. Each fish was measured for fork length and weight. Material was removed to study food (stomach and intestine), age and growth (scales and otoliths),

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Peter S. Maitland, Linda May, David H. Jones, C. Ross Doughty

sexual condition (gonads) and gill parasites. The total volume of food in the stomach and intestine of each fish was estimated. Food items were identified, counted and their relative bulk was assessed. Scales were found to be unsuitable for age determination. Otoliths were cleaned with a mounted needle and stored in methyl salicylate (Barbour & Einarsson, 1987). They were subsequently examined with a ×20 stereo microscope against a dark background. Opaque material was ground using 600-grade carborundum paper, after which growth bands were usually clearly visible. Age was determined from each otolith independently on three separate occasions. Otoliths were re-examined where discrepancies of more than one year were found. Age estimates were also checked at random with other workers. The age of each fish was taken as the number of dark bands counted in the otolith, modified to take into account progress through the growing season (after Barbour & Einarsson, 1987). Fork lengths of charr shorten by up to 5% during the first month of freezing and so the lengths of the Doon fish were corrected accordingly. Gonads were weighed (wet weight) to the nearest 0.01 g. The condition of the gonad was also recorded at weighing, including, for ovaries, the presence of resorbing eggs. Blood and tissue samples from fish caught in February and May 1987 were taken for electrophoretic analysis of allelic frequency as part of a separate study (Partington, 1988). Some meristic information (gill taker and branchiostegal ray counts) was also obtained from the samples. This has been used to examine the genetic relationships between some Welsh, English and the Loch Doon population of arctic charr (Partington & Mills, 1988). The fish populations of the three main inflows to Loch Doon were surveyed in September 1986 by electrofishing with pulsed DC gear powered by a 0.3-kVA petrol-driven alternator. No stop nets were used but where possible reaches with natural barriers were sampled. In addition, for comparative purposes, two physically similar but less acidic streams in adjacent catchments were fished. At each site, two or three reaches were fished once only, giving a total area sampled of 200-500 m 2. The fork length of all salmonids was measured.

WATER CHEMISTRY Many of the hill streams in this part of Scotland are called lanes. Two of the major inflows to Loch Doon, the Gala and Carrick Lanes, draining afforested catchments (60% and 31%, respectively) with similar granitic rocks, were similar in terms of water quality (Table 1). Both were acidic (pH 5.5-5"6) with low alkalinities and calcium concentrations. A third inflow, the

Arctic charr in southwest Scotland

173

TABLE 1 Selected Chemical D e t e r m i n a n d s (ion concentrations as mg/litre, conductivity as uS/cm) for Loch D o o n , its M a j o r Inflows and Outflow (means 1986-88) Sampling sites ~ L. Doon L2 pH Ca 2 + Mg 2÷ Na ÷ K+ AI C1 SO 2 Alkalinity Conductivity PO4-P NO3-N

5"69 0"86 0"90 4"08 0'39 ---37"8 <0-01 <0"10

L. Doon L6 5"97 1"04 0"99 4.21 0.40 ----38-8 <0"01 <0-10

Gala L. $1

Carrick L. $2

Garpel B. $3

R. Doon $4

5"57 1"04 0"63 3'75 0'40 0-085 5-6 4"48 0-46 36-4 . .

5"53 0"99 0"67 4-04 0.46 0"066 7'2 3-78 0-40 38-4

6"06 2-06 0"96 4.97 0.48 0'061 8"3 5"45 2"57 48"5 . .

5"94 1"34 0'83 4.39 0"43 0"080 7.7 4.55 1.07 41.0

. .

. .

a See Fig. ! for location o f sampling sites.

Garpel Burn, draining a catchment of Ordovician sedimentary rocks with less afforestation (16%), was less acidic (pH 6.06) and had a higher alkalinity and calcium concentration. Streams draining areas with rocks resistant to weathering (e.g. granites) are regarded as being particularly sensitive to acidification (Hammerton, 1988). Similarly, streams draining heavily conifer-afforested catchments are likely to be more acidic than those draining moorland or lightly afforested areas (Harriman & Morrison, 1982; Stoner et al., 1984). Water chemistry in the loch reflected conditions in the inflows. At the southern end of the loch, the mean pH was lower than at the northern end as a result of the proximity of the two largest and most acid inflows. Not surprisingly, the quality of the outflow was similar to that of the northern end of the loch. The loch's oligotrophic status was demonstrated by the low phosphate and nitrate concentrations, which were always below detection limits. It is difficult to assess the ecological implications of the measured aluminium concentrations. Aluminium speciation and toxicity to fish are pH-dependent (Schofield & Trojnar, 1980), with maximum toxicity at pH 5.2-5.4 (Baker & Schofield, 1982). Toxicity is mitigated by increasing aqueous calcium concentrations (Brown, 1983) and the presence of complexing agents such as organic acids (Driscoll et al., 1980). Although

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Peter S. Maitland, Linda May, David H. Jones, C. Ross Doughty

mean aluminium concentrations found during this study were above those known to cause harmful effects in brown trout (Sadler & Lynam, 1987), under the moderately humic conditions prevailing in Loch Doon and its inflows, much of the aluminium would have been in a less toxic, organically bound form. In addition, mean aluminium concentrations may be less important ecologically than the timing, intensity and duration of peak concentrations associated with acid episodes occurring at times of high stream flow (Reader & Dempsey, 1989). Peak aluminium concentrations recorded were 0-160mg/litre (R. Doon), 0.130mg/litre (Gala Lane), 0.100 mg/litre (Carrick Lane) and 0"105 mg/litre (Garpel Burn).

STREAM ECOLOGY Invertebrates

Invertebrate communities in the lower reaches of the two largest inflows, the Carrick and Gala Lanes, were very similar (Table 2). Both were dominated by Plecoptera and other groups were relatively unimportant. Ephemeroptera were uncommon and only Leptophlebia marginata and L. vespertina were found regularly; these species are known to be particularly tolerant of acid waters (Hendrey & Wright, 1976; Engblom & Lingdell, 1984; Raddum & Fjellheim, 1984). Baetis rhodani was recorded occasionally and solitary specimens of Ameletus inopinatus and Ephemerella ignita were taken from the Carrick and Gala Lanes, respectively. Such impoverished ephemeropTABLE 2 Percentage Composition (means of 6 surveys) of Major Invertebrate Groups in Loch Doon Inflows and Outflow (1986-88)

Sampling sites~ Gala L. S1 Bivalvia Oligochaeta Ephemeroptera Plecoptera Coleoptera Trichoptera Diptera Others

0 3.1 2'9 76.8 3.9 3'8 7-8 1.7

Carrick L. $2

0 7.6 1.0 63"8 7.6 5-6 11.9 2.5

a See Fig. 1 for location of sampling sites.

Garpel B. $3

20'3 5.1 2.9 11.3 4-2 10.3 45.5 0.4

R. Doon $4

13.0 3.3 1.8 17.2 0 35.4 22-9 6.4

175

Arctic charr in southwest Scotland

teran faunas are characteristic features of acid streams (Sutcliffe & Carrick, 1973; Harriman & Morrison, 1982). The Garpel Burn was very different from the other main inflows, both physically and in its invertebrate fauna. The beds of the Gala and Carrick Lanes consisted of clean gravel, pebbles, cobbles and granite boulders The Garpel Burn's bed of cobble and small stones contained substantial amounts of eroded peat particles, and its invertebrate fauna was dominated by Diptera (mainly Chironomidae) and the bivalve Pisidium. However, despite having a higher pH than the Carrick and Gala Lanes, Ephemeroptera were uncommon. Baetis rhodani was present in all the samples taken but it was rare to find more than one specimen per sample. Both Leptophlebia spp. were also present. The bed of the River Doon below the loch had heavy deposits of peat particles. The invertebrate fauna was dominated by net-spinning Trichoptera, particularly Polycentropus flavomaculatus and Neureclipsis bimaculata, with Chironomidae, Plecoptera and Pisidium spp. also common. Filter feeders such as Polycentropidae are frequently abundant in lake outflows (Hynes, 1970) and N. bimaculata is usually restricted to this habitat (Edington & Hildrew, 1981). Again, Ephemeroptera were rare, being generally restricted to Baetis rhodani, apart from one sample in August 1987 which contained Ephemerella ignita and Baetis muticus. In view of the fact that Mollusca are often considered to be among the most sensitive invertebrate groups to acid waters, the c o m m o n occurrence of Pisidium spp. in the River D o o n and Garpel Burn may seem surprising. However, certain Pisidium spp. can tolerate waters as acidic as pH 5"0 (Okland, 1980). Fish Brown trout was the only fish species found in the Gala and Carrick Lanes (Table 3). In contrast, the Garpel Burn supported a large population of TABLE

3

Fish Caught in Loch Doon Inflows and Control Streams (September 1986)

Mean pH Area fished (m 2) Trout caught Trout density/100 m 2 Other fish: minnow loach eel

Gala L.

Carrick L.

Garpel B.

R. Girvan

R. Stinchar

5.57 483 18 3"7

5"53 391 19 4-9

6"06 426 8 1"9

6"37 212 50 23'6

6"67 198 60 30"3

--

+

+

--

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Peter S. Maitland, Linda May, David H. Jones, C. Ross Doughty

minnows and some stone loaches as well as trout. No salmon were caught, although information from the local angling association suggests that salmon were at one time present in both the Gala and Carrick Lanes, and that the Carrick Lane had been stocked with salmon alevins in the past. It is possible that both the major inflows are now too acidic to support salmon. A survey of upland streams in England and Wales (Turnpenny et aL, 1987) showed salmon to be absent from streams with a mean pH of less than 6.0. Fluctuating water levels in the loch may also have had an adverse effect on salmon populations since they are not able to surmount the falls at the mouth of the Carrick Lane when the loch level is low. Densities of trout were very low in all three inflow streams examined and were much higher in the upper reaches of the adjacent and less acidic Water of Girvan and River Stinchar (Table 3). The presence of 0 + and 1 + trout in the Loch Doon inflows showed that trout were still spawning there successfully. The Garpel Burn's exceptionally poor trout population may have been due to the lack of suitable spawning sites--in particular, areas of gravel free from deposited peat particles.

LOCH ECOLOGY

Algae The surface sediment diatoms at Loch Doon were sampled in 1984 by the Department of Geography at University College London (R. Flower, pers. comm.). The sediments were dominated by Asterionella nalpii and Tabellaria flocculosa, two species indicative of a moderately acid lake and inferring that this loch is less acidic than others in the area (e.g. Loch Enoch and Loch Grannoch).

Invertebrates The invertebrate fauna of the stony littoral zone of the loch was very sparse. It was not unusual to find just a few individuals of two or three species at any one site on a particular sampling occasion. This is almost certainly the result of the widely fluctuating water levels (Smith et al., 1987). Oligochaete worms were the most conspicuous group (Table 4), especially Enchytraeidae and Lumbriculidae. The naidid Stylaria lacustris was c o m m o n in August samples. Of those groups generally regarded as being sensitive to acidification, the Mollusca were represented by Pisidium spp. and the semi-aquatic Lymnaea truncatula, while Leptophlebia marginata and L. vespertina were the only Ephemeroptera found regularly. A single Baetis rhodani was recorded from the southern end of the loch in April 1986.

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Arctic charr in southwest Scotland TABLE 4

Macroinvertebrates from the Stony Littoral of Loch Doon (1986) L5

L7

1 0

0 0

2 2

0 23 6

0 0 19

0 8 8

0 1 24

1 0

0 0

0 0

0 0

1 1

72 3

28 0

13 0

27 0

76 0

8 0

3 1

0 0

0 0

0 0

3 0

4 0

80 56 52 0

0 0 1 0

164 1 6 0

296 23 150 0

217 19 35 1

86 6 39 0

Eiseniella tetraedra

0

0

0

2

0

1

Hydracarina

5

1

4

97

0

10

Baetis rhodani Leptophlebia marginata Leptophlebia vespertina Nemoura cinerea Chloroperla torrentium Micronecta poweri

1 0 1 3 0 0

0 1 2 1 1 1

0 3 1 0 0 0

0 5 0 0 1 1

0 5 1 0 0 0

0 6 0 1 0 0

Dytiscidae

4

0

5

1

0

1

Potamonectes depressus Oreodytes septentrionalis Cyrnus flavidus

2 1 0

2 1 0

0 9 1

2 13 0

1 1 0

1 2 2

0 0 0 0 0 56

0 0 0 0 0 4

6 0 0 0 0 5

0 6 1 0 1 9

0 0 0 0 0 2

1 0 0 1 0 4

0

0

0

0

1

0

Phagocata vitta Lymnaea truncatula Pisidium Chaetogaster diaphanus Nais communis/variabilis Nais elinguis Slavina appendiculata Stylaria lacustris

Tubificidae Spirosperma ferox Aulodrilus pluriseta

Enchytraeidae Lumbriculus variegatus Stylodrilus heringianus

Lumbricidae

Tipulidae Tipula sp. Limoniinae Eloephila sp. Hexatoma sp. Chironomidae Dolichopodidae

L1

L2

L3

0 0

0 0

0 0

64 0 8

0 9 2

0 0

L4

Numbers are totals caught in four surveys (April, June, August, November). See Fig. 1 for location of sampling sites. T h e rotifer z o o p l a n k t o n in F e b r u a r y a n d J u l y 1987 w a s d o m i n a t e d b y the c o s m o p o l i t a n species K e r a t e l l a c o c h l e a r i s , while in A p r i l 1987 the m o s t c o m m o n rotifer w a s K e l l i c o t t i a l o n g i s p i n a (Table 5). T h e o l i g o t r o p h i c n a t u r e o f the l o c h is reflected b y the p r e s e n c e o f K. l o n g i s p i n a a n d the l o n g - s p i n e d f o r m o f K. c o c h l e a r i s t h r o u g h o u t the s a m p l i n g p e r i o d a n d the relatively h i g h a b u n d a n c e o f K e r a t e l l a h i e m a l i s in winter. A n o t a b l e o c c u r r e n c e w a s t h a t o f

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Peter S. Maitland, Linda May, David H. Jones, C. Ross Doughty

TABLE 5 Relative Abundance (%) of Rotifer Zooplankton in Open Water Samples from Loch Doon

Species

10 February 1987

30 April 1987

30 July 1987

57"5 18.4 0"4 0 18"0 0'9

30"8 0 0 25"8 38"8 3"5 1-1 0 0 0 0

59"3 0 0 0 12'3 0 6-8 1-2 0 0 20'4

Keratella cochlearis Keratella hiemalis Keratella serrulata Keratella quadrata Kellicottia longispina Synchaeta kitina Polyarthra dolichoptera Polyarthra minor Collotheca sp. Trichotria ?tetractis Trichocerca sp.

0 0 3'9 0"9 0

Keratella serrulata, which is found only in humic acid waters. Though found in low numbers here, its occurrence in the February samples most probably reflects the increased acidity of the water at that time. The crustacean zooplankton (Table 6) was rich and the community of nine species collected showed a similar structure to several other large lochs in Scotland--Lyon, Tay, Earn, Ness and Shiel--which range from dystrophic and oligotrophic to mesotrophic (Jones, 1985). The diaptomid copepod Eudiaptomus gracilis was dominant overall, followed closely by the cladoceran Daphnia hyalina. Cyclops abyssorum, Bosmina coregoni and TABLE 6 Relative Abundance (%) of Crustacean Zooplankton in Open Water Samples from Loch Doon

Species Cyclops abyssorum Eudiaptomus gracilis

30 April 1987

30 July 1987

6 October 1987

8"1 69"7

3-4 26"6

+ 47"2

0

16"3

0

7"1

30"8 0 1'1 1'7 2"0 + 18-2

52"5 0"3 + + + 0 0

(male, female copepodite V)

Arctodiaptomus laciniatus (male, female copepodite V)

Daphnia hyalina var. lacustris Bosmina coregoni var. obtusirostris Ceriodaphnia quadrangula Bythotrephes longimanus Leptodora kindti Holopedium gibberum

0 0 0

Juvenile copepodites (I-IV)

0

8"9 6-2

179

Arctic charr in southwest Scotland

Ceriodaphnia quadrangula were all fairly abundant in spring, but were present only in low numbers in summer and autumn. Arctodiaptomus laciniatus was abundant in summer but was not recorded in spring or autumn. Bythotrephes longimanus, Leptodora kindti and Holopedium gibberum were recorded in July and October but were never numerically important. Arctic charr

Age and growth The majority of fish caught were 3-5 years old. The oldest were 8 years old and very few were less than 3 years. The male: female ratio was 1:1 over most age classes, though males were in general larger than females and the 8 + fish were all males. A generalised growth curve for the population is given in Fig. 2. Young charr seem to grow rapidly duringtheir first three years of life and then, once over 230 m m in length, the growth rate falls and is subsequently slower. This is in contrast to growth in some other Scottish lochs, e.g. Meallt, Builg and Doine (Barbour & Einarsson, 1987), and Awe, Borallie, Insh and Rannoch (Maitland et al., 1984), where charr of similar size during the first few years maintain a steady increase in length throughout their lives. Increase in weight showed a similar trend to that for length. Body weight increased rapidly over the first three years and then levelled off from the

260'

:s

240

z -122C (.9 z IJ.I ..-I

20C

180

I

I

I

I

I

I

I

i

I

1

2

3

4

5

6

7

8

¢3

AGE

Fig. 2.

IN Y E A R S

Growth curve of arctic charr in Loch Doon. The lengths indicated are fork lengths.

180

Peter S. Maitland, Linda May, David H. Jones, C. Ross Doughty

fourth growing season onwards. Again this contrasts with the available data from other Scottish lochs. Food and feeding

A strong seasonal pattern was observed in both the volume and composition of the food of charr in Loch Doon. Gut volume was lowest in February, increasing to a maximum in July and declining again in the post-spawning fish in late October. Food changed from benthic material in October, February and April/May to almost 100% plankton in July (Table 7). However, in October much of the benthic material was planktonic in origin--the ephippia of Daphnia hyalina forming more than 90% of all food items found. The food items in the guts also gave some indication of where the fish had been feeding. Specimens collected at spawning time contained only chironomids and Eurycercus larnellatus--indicating that they had been feeding inshore. There was no evidence of them feeding on their own eggs, though trout were found in subsequent years to be gorging on charr eggs at this time. In February, only 19% of the guts contained food--mainly chironomids and fragments of peat--probably taken off the bottom in deep water. In May, 92% of the guts had food in them, although the volume was low. Again, the diet consisted mainly of bottom organisms--the egg cocoons of oligochaete worms, benthic copepods, chironomids and bivalve molluscs (Pisidium). By July, when fish were in much better condition (see below), the TABLE 7

Percentage Occurrenceof Food Items in the Guts of Arctic Charr from Loch Doon Food item

Bivalvia Oligochaeta (cocoons) Daphnia hyalina Bosmina coregoni Eurycercus lamellatus Bythotrephes longimanus Holopedium gibberum Cyclops albidus Arctodiaptomus laciniatus

Ephemeroptera Trichoptera Corixidae Chironomidae Number of charr guts

24 October 1986

11 February 1987

7 May 1987

31 July 1987

0

0

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Arctic charr in southwest Scotland

181

guts were mainly full of plankton, especially Daphnia hyalina and, to a lesser extent, Bythotrephes longimanus. Cladocera are the dominant food organisms of most plankton-feeding charr populations (Swynnerton & Worthington, 1940; Campbell, 1976; Frost, 1977; Klemetsen, 1983; Maitland et al., 1984; Walker et al., 1988) although they may not dominate the plankton. In July 1987, Daphnia hyalina formed almost 100% of the diet of charr but only constituted 31% of the crustacean zooplankton (Table 7). The predatory cladoceran Bythotrephes longimanus was also important in the diet at this time although it was scarce in the plankton. Thus arctic charr appear to feed selectively on these two cladocerans in the summer.

Condition The relationship between weight and length in a fish may be defined as W= aL", where a is a constant and n ranges between 2.55 and 4 (Lagler et al., 1962). The commonly used exponent is 3, yielding a Condition Factor (Ponderal Index) formula of K = W/L 3. Thus the most satisfactory method of comparing the 'plumpness' or 'leanness' of a stock of charr, at different times of the year or between years, is to use the Condition Factor K--- W/L 3 (Johnson, 1980). Condition Factors have been calculated for the Loch Doon charr collected during this study and analysed separately for males and females. The condition of both males and females declines after spawning in October (Fig. 3) and is at its lowest during winter and spring. It rises again during summer and is at its highest in both sexes in the late summer just before spawning. The general condition of fish appears to be good when compared to other charr populations (Johnson, 1980). Condition Factor could be a good indicator of stress. Perch in Ontario lakes with pHs above 5-0 showed a higher Condition Factor than those in lakes with pHs below 5"0. Rosseland et al. (1980) observed that the Condition Factor in fish may change in response to acid stress independent of growth.

Reproduction The pattern in the gonad cycle is similar in both male and female charr (Fig. 4). The size of both testes and ovaries is most variable at spawning time, when some fish may be spent (and gonad size at a minimum) but others just ready to spawn. After spawning, during the winter period, the gonads are small (usually less than 1% of the body weight) but they start to develop again during the spring and are well developed (several per cent of the body weight) by late summer. The ovaries of female fish in spring and early summer frequently contain old resorbing eggs from the previous spawning. Netting carried out in October in 1986, 1987 and 1988 indicated that

182

Peter S. Maitland, Linda May, David H. Jones, C. Ross Doughty 1"6

o

¢...,)
tt

Z O 0.8 Z

o 0.4

MONTHS

Fig. 3. Condition factors of arctic charr in Loch Doon at four times of the year. The mean, minimum and maximum values are shown, the males on the left and the females on the right in each case.

IO

LLI N 6¸ ,,m < z 4" O

O

S O

N D d

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Fig. 4. The gonad sizes of arctic charr in Loch Doon at four times of the year, expressed as percentages of body weight. The mean, minimum and maximum values are shown, the males on the left and the females on the right in each case.

Arctic charr in southwest Scotland

183

spawning follows the usual pattern among charr in Scottish lochs (Maitland et aL, 1984) and takes place along much of the stony shore line of Loch Doon. There are always large numbers of ripe males in the littoral zone at this time, but relatively few females, most of which apparently wait further offshore until they are fully ripe. It appears that the actual period of spawning extends over a short period, probably some 5-10 days in the first half of October in most years. There is no evidence for a double spawning period as with the charr population in Windermere (Frost, 1965).

The fishery Relatively little has been published concerning arctic charr in Loch Doon (or any of the other southern Scottish populations). Fortunately, however, there is some unpublished information available with which to compare the results of recent work there (Maitland, 1988a,b; May & Jones, 1988). As part of his extensive collecting of charr (Friend, 1956, 1959), the late G. F. Friend took a special interest in Loch Doon (Friend, 1958). Originally, only one museum specimen was available and although he was unsuccessful in catching fish in Loch Doon when he netted in 1953, in May 1954 he was given two specimens caught by anglers. Two further fish were presented to him that year from the same source and in subsequent years virtually all fish caught at the annual angling competition were sent to him. Unfortunately Mr Friend died before completing his research (Maitland, 1981), but his material and data were subsequently passed to the authors and

5 t~o i.u

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-1-zI--3" /~ F-< (.3

2"' 1Oj .-'"....,,..;."""..-"65;....................,........,...~-..,y./",' -....,..... 75 85, YEARS

Fig. 5. Total catches of brown trout (solid line) and arctic charr (dotted line) at Loch Doon from 1956 to 1985 from the annual championship of the Ayrshire Angling Association.

184

Peter S. Maitland, Linda May, David H. Jones, C. Ross Doughty 300

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,

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'

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'

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YEARS F o r k lengths o f arctic charr (mean, m i n i m u m and m a x i m u m values) in samples f r o m 1954 to 1988.

part of this has now been published (Fryer, 1981; Maitland et al., 1984). A few further samples of charr were subsequently caught by the anglers at Loch Doon and also passed to the authors. In addition, details of all the catches from their annual competition have been made available by the Ayrshire Angling Association (Fig. 5). 200

¢n 150 < (D z --

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Fig. 7.

6'5

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YEARS Mean weights of brown trout caught at Loch Doon from 1956 to 1988 from the annual championship of the Ayrshire Angling Association.

185

Arctic charr in southwest Scotland

niJ.i nn z~ z

'

6'5

'

'

is

YEARS

Fig. 8.

Mean numbers of brown trout caught per angler at Loch Doon from 1956 to 1984 at the annual championship of the Ayrshire Angling Association.

Apart from their intrinsic interest, these samples have provided valuable historic information on the state of the charr population at Loch Doon over the last few decades. One of the most outstanding features has been the change in the size of the adult charr over this period (Fig. 6). Whereas the mean length of fish during the 1950s was 17-18 cm it is now substantially larger (22-23 cm). The condition of such fish at different times over this period is also of relevance (Johnson, 1980). A similar phenomenon seems to have taken place in the brown trout population, judging by weight data obtained from the Ayrshire Angling Association (Fig. 7). There is no indication of any similar changes in unacidified lakes, e.g. Windermere (Frost & Kipling, 1980). Significantly, the increase in the mean weight of trout coincides with a decrease in the catch per unit effort by the anglers (Fig. 8).

THREATS TO ARCTIC C H A R R IN LOCH DOON Acidification Acid precipitation has resulted in severe damage to fish stocks in Scandinavia. In southwest Sweden, trout, arctic charr, roach Rutilus rutilus (L.) and minnow have all been affected (Almer et al., 1974). Atlantic salmon have been eliminated from several Swedish rivers (Wright et al., 1977). Acid

186

Peter S. Maitland, Linda May, David H. Jones, C. Ross Doughty

precipitation has also devastated fish populations in southern Norway, where the principal fish species affected are Atlantic salmon, trout, arctic charr and brook charr Salvelinusfontinalis (Mitchill) (Almer et al., 1974). One of the most characteristic effects of acidification on northern fish populations is the failure of recruitment of new age classes into the population (Rosseland et al., 1980; Harvey, 1982). This is manifested in an altered age structure and reduction in population size. The latter reduces intra-specific competition for food, where this resource is limiting, and results in increased growth and improved condition of survivors (Beamish & Harvey, 1972). As well as pH, the total ion content of the water is important for fish survival (Brown, 1982): higher concentrations of ions increase survival time under otherwise similar conditions--including pH. In soft water it is suggested (Wright el al., 1977) that the critical pHs are 5.0-5-5 for salmon, 4.5-5.0 for arctic charr and sea trout, and 4.0-4.5 for brown trout. Kelso & Minns (1981) have produced a general scheme which would indicate that there should be some concern for the future of fish in Loch Doon. Arctic charr and trout are among the least tolerant of freshwater species (Almer et al., 1974) and this emphasises the present fragile nature of Loch Doon. It seems likely, in view of the advanced nature of acidification in the upper parts of the Loch Doon catchment, that action is necessary to reverse the trend. The only potential solution would seem to be some form of liming. Considerable success has been achieved with liming in Scandinavia in the past and recently a number of successful trials have taken place in catchments relatively near Loch Doon, at Loch Dee (Burns et al., 1984) and Loch Fleet (Central Electricity Generating Board, 1988). Lakes in two small watersheds in southwest Norway were formerly characterised by dense populations of small arctic charr and brown trout (Andersen et al., 1984). However, by 1983, the acidified headwater lakes had lost their fish stocks, while the remaining fish stocks were in various stages of local extinction. Arctic charr were characterised by a dominance of old fish in which growth and condition were both good. Arctic charr were more affected than brown trout by the acidification. In Sweden, Stora Holmevatten was a strongly acidified oligotrophic lake whose entire fish population, including 'a unique genetic stock' of arctic charr, had disappeared (Hasselrot et al., 1984). After liming, pH and alkalinity increased and aluminium levels decreased. New stocks of arctic charr were introduced and successfully established themselves, spawning within two years. Charr had disappeared from many lakes in Sweden and of 26 charr lakes investigated in 1983 (Nyberg, 1988), liming had been carried out in 23. Charr were successfully reintroduced to four lakes where the species had previously been wiped out by acidification.

Arctic charr in southwest Scotland

187

It is clear from the Scandinavian research that it is perfectly feasible to reverse severe acidification by the use of lime and re-establish stocks of arctic charr. Management by this means at Loch Doon is at present being assessed by one of the authors, but the large size of the loch makes the measure an expensive one. The most realistic approach, for various reasons, is not to attempt catchment liming but to consider the use of lime wells or regular dosing on one of the major inflows. Afforestation Maitland et aL (1990) have recently reviewed the impact of coniferous afforestation and forestry practice on freshwater habitats in Great Britain. The effects of each stage of the forestry cycle--ground preparation, tree planting to canopy closure, the maturing crop and felling--may all have an impact on local fresh waters. The physical aspects of afforestation affect the hydrology of streams (loss of water through interception and evaporation, higher flood peaks and lower drought levels), the erosion of sediments, and reduced summer water temperatures. The principal chemical changes in fresh waters include increased nutrient levels and the acidifying effect of air pollutants which are intercepted and transferred to adjacent water courses. Much of the biological damage is due to high amounts of aluminium leached from the acid soils. These physical and chemical effects combine in various ways to affect the plants and animals. Changes in the hydrology and ambient water temperatures tend to make conditions in streams more extreme for most biota. Turbidity decreases plant growth. Increased nutrients alter the composition of plant communities and cause problem crops of algae. Acidification affects plant and invertebrate communities and may eliminate fish. There are various forest management practices which can alleviate some of these effects. They include care in road construction, ploughing and drainage systems during ground preparation, with particular emphasis on preventing drains going directly into streams or lakes. Conifers should not be planted right up to the edges of waters, but buffer strips should be left and possibly actively managed in some cases. The acidification effects may be ameliorated by liming, but in particularly sensitive catchments afforestation should be avoided altogether. It seems virtually certain that the recent extensive afforestation in the Loch Doon catchment will have exacerbated the acidification already taking place in the headwaters. Here, Loch Enoch, well above the forest and once well populated with brown trout, is now highly acid and fishless (Maitland et al., 1987). It appears that the same may be happening at Loch Doon, but at a

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Peter S. Maitland, Linda May, David H. Jones, C. Ross Doughty

slower rate. The developing forest surrounding the loch seems certain to increase the acidic input as further planting proceeds and the canopy of the developing new forest closes. Further planting should only take place with careful consideration of its impact on the loch. Full attention should be paid to modern practices aimed at avoiding the acidifying effects of afforestation.

Hydrology Hydro-electric schemes can have deleterious effects and this may have been the case at Loch Doon, especially as far as stocks of salmon in the loch and its headwaters are concerned. Virtually no salmon have entered the loch in recent years. However, arctic charr may be less influenced by the fluctuating water levels which affect the main feeding grounds of trout in the littoral. Though fluctuating water levels devastate the littoral biota (Smith et al., 1987), the plankton is less affected and charr still have their main food source. However, in view of the large mortality, discussed below, among the arctic charr in Loch Doon at a time of extreme low level in late summer it would seem important to retain reasonable levels at this time.

Angling Loch Doon is a popular loch for both local anglers and those from further afield. In general, angling poses certain conservation problems for fish populations, notably those concerned with litter (especially old nylon), disturbance, habitat damage, the use of piscicides, the control of predators and the introduction of new species (Maitland & Turner, 1987). The most relevant of these problems at Loch Doon has been the introduction of perch, now abundant there and supposed to have been introduced by anglers from England. The first perch recorded from the loch were seen in 1970 and as they are more tolerant of acid stress than charr they may be harmful in a number of ways (e.g. as competitors or predators)--especially if the charr are under stress. To some extent, the anglers at Loch Doon are of benefit to the system there and the Ayrshire Angling Association has been most co-operative in relation to conserving arctic charr. As noted above, the main information on trout stocks and the older chart material has been collected by this Association and its members have recently agreed to return all charr caught to the loch instead of taking them with the trout as previously. In fact, the anglers have always taken so few charr that fishing has never posed any kind of threat to the stock there. It is likely that the stock of brown trout at Loch Doon benefits from the

Arctic charr in southwest Scotland

189

presence of arctic charr. Trout collected in October 1988 when chart were spawning were found to be so full of charr eggs that these were being regurgitated in considerable numbers as the trout were being removed from the net. The reverse would not happen when trout are spawning because at that time the trout migrate into the burns where there are no charr. Additionally, larger trout are 'known to eat charr (Hardie, 1940) and it is believed that the latter are the main prey of the large ferox trout found in many Scottish lochs (Campbell, 1979), including Loch Doon. Mortalities In September 1975 an extensive mortality of arctic charr took place throughout Loch Doon and its outflow (Clyde River Purification Board, 1975; G. S. Scott, pers. comm.). The first reports of the problem were received on 12 September 1975, when a large number of dead fish were seen on the west shore of Loch Doon. Numbers of dead fish (estimated at c. 500) were also seen in the river downstream of the dam and several shoals of fish were observed in the spillway pool. Some of these fish were examined and found to be suffering from fin rot and severe fungal infection. More fish were collected on 16 September 1975 and these showed heavy parasite infestations (notably Diphyllobothrium), considerable bacterial infection of the gills and body surface and damage to the liver and kidneys. The general conclusions from the mortality were as follows. Due to abnormally dry weather conditions at the time and the large volumes of compensation water released from Loch Doon, water levels had fallen by about 30 m. The population of arctic chart, vulnerable to stress because of imminent spawning, were susceptible to fin rot and other conditions which spread through the population, helped by the crowding of the fish and high water temperatures. Some charr, which were found in the river downstream of the dam, were extensively damaged because they had presumably passed through the penstocks in the dam and not the fish pass, which was not in use at the time. It seems likely with the knowledge now available that the population may already have been suffering from acid stress, and was therefore particularly vulnerable.

DISCUSSION Changes in recent decades Monthly pH records from the River Doon downstream of Loch Doon for the period 1975-88 (Fig. 9) show that from 1975 to 1982 annual mean pH

190

Peter S. Maitland, Linda May, David H. Jones, C. Ross DoughO'

7'5'

7'0

6'5 -r o.

6'0

5.5

5'0

76

78

80

82

84

86

88

YEARS

Fig. 9.

Annual mean pH values (including standard deviations) of the River Doon ($4) below Loch Doon from 1975 to 1988.

remained fairly steady, varying between pH 6.96 and 7.32. However, between 1982 and 1986 mean pH dropped sharply to 5"56 before recovering to 6.24 in 1988. The results from the water chemistry were more or less as expected in view of the local geology and what was previously known about Loch Doon and adjacent systems (Hammerton, 1988). Broadly speaking, the tributaries entering the south end of the loch (via the Gala and Carrick Lanes) are acidic and poor in nutrients whereas those entering nearer the north end (Garpel Burn and the outflow from Loch Muck) are less acid and carry more nutrients. The Carrick Lane system originates in the acidified Loch Enoch in the granite hills south of Mullwharchar. Brown (1982) and others have noted that the critical pH levels which cause stress and mortality among salmonid populations are between 5.0 and 5-5. The Carrick and Gala Lane systems frequently fall within this range and fish populations there must be vulnerable. However, it is known that low densities of brown trout do still exist in these tributaries. The waters entering the north end of the loch are heavily stained from humic products and carry much more calcium than the southern tributaries. They are therefore probably very important in helping to buffer the waters of Loch Doon from the more harmful effects of the acidic water from the southern lanes (Henriksen, 1979). In general, the chemistry of the outflow from Loch Doon does reflect such a mix, being generally intermediate between that of the two northern and the two southern tributaries. There is also evidence from the macroinvertebrate records that the loch outflow has become more acidic in recent years (Fig. 10). Until the mid-

Arctic charr in southwest Scotland

191

C {1) t.u ILl 0.. t,o

di

e.

f

65 . . . .

m

70

. . . .

7'5 . . . . YEARS

80 . . . .

815 . . . .

Fig. 10. Occurrence of the following acid-sensitive invertebrates in the River Doon ($4) below Loch Doon from 1966 to 1988: (a) Lymnaea; (b) Ancylus; (c) Ephemerella; (d) Paraleptophlebia; (e) Heptagenia; (f) Rhithrogena; (g) Ecdyonurus; (h) Baetis (above: spring samples; below: all samples).

1970s, acid-sensitive Ephemeroptera of the genera Ecdyonurus, Heptagenia and Rhithrogena were present at various times. Single occurrences of the gastropods Lymnaea peregra and Ancylusfluviatilis were also noted. None of these species has been recorded since 1976. Apart from single occurrences of Ephemerella ignita and Paraleptophebia sp. no other mayfly except Baetis (probably all B. rhodani except for the B. muticus found in 1987) have been found since 1976. It is probably significant that no Baetis spp. were found in spring samples from 1978 to 1985 whereas they were definitely absent from samples taken at other times of the year only in 1984 and 1985. No data are available for 1981 and 1982. Baetis rhodani has two generations a year, one emerging in the spring and a second in late summer (Elliott, 1967; Wise, 1976). The spring-emerging generation would be most at risk from acid pulses occurring during the winter and early spring associated with high rainfall or snow melt. During late spring and early summer, ovipositing females of B. rhodani could recolonise the river from nearby non-acid streams and the developing nymphs of the summer generation would be less likely to encounter lethal acid episodes. Although both water chemistry and invertebrate data suggest a recent acidification of Loch Doon, the former indicate a rapid acidification beginning in the early 1980s while the latter appear to show that the loch became significantly more acid in the mid-1970s. It is possible that in the period from about 1976 to 1982 acid episodes occurred too infrequently to

192

Peter S. Maitland, Linda May, David H. Jones, C. Ross Doughty

be detected by monthly chemical monitoring but were sufficient to induce significant changes in the invertebrate fauna. However, chemical evidence from another source (Harriman et al., 1987) shows that in 1978-79 Loch Doon had a mean pH of 5"8, more than one unit lower than suggested by Clyde River Purification Board records, which would be more in accordance with the biological findings. There is no obvious explanation (e.g. change in methodology) to account for the discrepancy between the two sets of data. The evidence would clearly suggest that Loch Doon is acidifying and that the arctic chart may be under considerable threat. The historical chemical data indicate that the water is more acid than formerly. In addition, the average size ofcharr (and also of trout) in the loch is significantly larger than a decade ago, and although this cannot yet be specifically attributed to acidification, it is certainly one of the characteristic features of fish populations affected by it. For these reasons, and the fact that the arctic charr population in Loch Doon has had a large mortality in the recent past, the conservation situation is regarded as urgent and appropriate management plans should be developed.

Stock transfer One of the most positive areas of management for endangered stocks of fish lies in the establishment of new populations---either to replace those which have become extinct or to provide an additional safeguard for valuable stocks in threatened waters (Maitland, 1985). Any species which is found in only a few waters could be in potential danger and the creation of additional independent stocks is an urgent and worthwhile conservation activity. The stock of arctic charr in Loch Doon is clearly a case where the creation of new stocks is valid. This can be done without any threat to the existing stocks. It is possible to obtain substantial numbers of fertilised eggs by catching and stripping adult fish during their spawning period. The adults can then if necessary be returned safely to the water to spawn in future years. Fortunately, most fish produce an enormous excess of eggs and so substantial numbers can be taken at this time without harm. Having identified an appropriate water in which to create a new population this can be initiated by placing the eggs there, or hatching them in a hatchery and introducing the young at various stages of development. Depending on the state of the parent stock, adults may in some cases also be moved. Such a procedure is already underway with arctic charr at Loch Doon. In the autumns of 1986, 1987, 1988 and 1989 fertile eggs were successfully obtained from the adult fish. These eggs were hatched under controlled conditions and numbers of young fish and some adults have been introduced to two large waters in the Scottish Borders--Megget and Talla Reservoirs. It

Arctic charr in southwest Scotland

193

is believed that these will provide ideal conditions for new populations. Megget Reservoir is linked to St Mary's Loch, which formerly had a population of arctic charr, now extinct (Maitland e t aL, 1984). It is very satisfactory to note here that the adult fish placed in Talla Reservoir have already bred there, for young charr were collected in January 1990 which could only have come from spawning by adults in the autumn of 1988.

CONCLUSION In conclusion, there are clear indications that the charr in Loch Doon may be under considerable threat, even in the short term. The historic chemical data indicate that the water is now more acid than formerly, and samples taken during this study indicate that the system is acidifying. In addition, the average size of chart and trout is significantly larger than a decade ago, and although this cannot yet be specifically attributed to acidification, it is certainly one of the features offish populations affected by it. The situation is complicated by severe water level fluctuations associated with electricity generation.

ACKNOWLEDGEMENTS The research carried out at the Fish Conservation Centre and the Institute of Freshwater Ecology was done under contract to the Nature Conservancy Council. We are grateful to Mr J. P. Burlison, who initiated this part of the research, and to Dr E J. Boon for advice during this study. Some of the work carried out by Clyde River Purification Board was done under contract to the Department of the Environment. Permission to work on Loch D o o n and its tributaries was given by the South of Scotland Electricity Board (Mr K. M. McKay) and the Forestry Commission (Mr A. T. Jones), respectively. Thanks are also due to the Ayrshire Angling Association and its secretary, Dr D. D. Muir, for advice, catch data and cooperation during the work. The previous secretary, Mr J. Reid, was instrumental over many years in providing valuable specimens of arctic charr caught by anglers to the late Mr G. F. Friend and later to one of the authors. Mr G. S. Scott also gave detailed diary records of the charr mortality incident. Valuable information on charr in the area has been supplied by Sir Edward Hunter-Blair. Permission to introduce arctic charr to Megget and Talla Reservoirs has generously been given by Lothian Regional Council, and we are particularly grateful to Mr A. D. Jamieson for advice and to Mr R. Paterson and Mr R. F. B. Clunie for their help at the reservoirs concerned.

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Peter S. Maitland, Linda May, David H. Jones, C. Ross Doughty

REFERENCES Almer, B., Dickson, W., Ekstrom, C., Hornstrom, E. & Miller, U. (1974). Effects of acidification on Swedish lakes. Ambio, 3, 330-6. Andersen, R., Muniz, I. P. & Skurdal, J. (1984). Effects of acidification on age class composition in arctic charr Salvelinus alpinus (L.) and brown trout Salmo trutta L. in a coastal area, SW Norway. Rep. Inst. Freshwat. Res. Drottning., 61, 5-15. Avondhu (1951). The fishes of Lough Melvin. Salm. Trout Mag., 132, 153-6. Baker, J. P. & Schofield, C. L. (1982). Aluminium toxicity to fish in acid waters. Water Air Soil Pollut., 18, 289-309. Barbour, S. E. & Einarsson, S. M. (1987). Ageing and growth of charr, Salvelinus alpinus (L.), from three habitat types in Scotland. Aquacult. Fish. Manage., 18, 63-72. Beamish, R. J. & Harvey, H. H. (1972). Acidification of the La Cloche Mountain Lakes, Ontario, and resulting fish mortalities. J. Fish. Res. Bd Can., 29, 1131-43. Brown, D. J. A. (1982). The effect o f p H and calcium on fish and fisheries. Water Air Soil Pollut., 18, 343-51. Brown, D. J. A. (1983). Effect of calcium and aluminium concentrations on the survival of brown trout Salmo trutta at low pH. Bull. Environ. Contain. Toxicol., 30, 582-7. Burns, J. C., Coy, J. S., Tervet, D. J., Harriman, R., Morrison, B. R. S. & Quine, C. P. (1984). The Loch Dee Project: a study of the ecological effects of acid precipitation and forest management on an upland catchment in south-west Scotland, 1. Preliminary investigations. Fish. Manage., 15, 145-67. Campbell, R. N. (1979). Ferox trout, Salmo trutta L., and charr, Salvelinus alpinus (L.), in Scottish lochs. J. Fish Biol., 14, 1-29. Campbell, R. N. B. (1976). Examinations of, and comparisons between, the food of two Hebridean populations of charr Salvelinus alpinus (L.), one allopatric, the other sympatric with trout Salmo trutta (L). BSc thesis, University of Aberdeen. Central Electricity Generating Board (1988). The Loch Fleet Project. Central Electricity Generating Board, London. Child, A. R. (1977). Biochemical polymorphism in charr Salvelinus alpinus L. from Llynnau Peris, Padarn, Cwellyn and Bodlyn. Heredity, 38, 359-65. Child, A. R. (1984). Biochemical polymorphism in charr Salvelinus alpinus L. from three Cumbrian lakes. Heredity, 53, 249-57. Clyde River Purification Board (1975). Annual Report. Clyde River Purification Board, East Kilbride. Day, E (1887). British and Irish Salmonidae. Williams & Norgate, London. Driscoll, C. T., Baker, J. P., Bisogni, J. J. & Schofield, C. L. (1980). Effect of aluminium speciation on fish in dilute acidified waters. Nature, Lond., 284, 161-4. Edington, J. M. & Hildrew, A. G. (1981). A key to the caseless caddis larvae of the British Isles with notes on their ecology. Scient. Pubis Freshwat. Biol. Assoc., 43, 1-91. Elliott, J. M. (1967). The life histories and drifting of the Plecoptera and Ephemeroptera in a Dartmoor stream. J. Anim. Ecol., 36, 343-62. Engblom, E. & Lingdeil, P. E. (1984). The mapping of short-term acidification with the help of biological pH indicators. Rep. Inst. Freshwat. Res. Drottning., 61, 60-8.

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