Peter S. Maitland

The conservation of freshwater fish: Past and present experience

Abstract The conservation of fish and fish communities has received little attention relative to other vertebrates. Yet across Eurasia and North America, numerous important stocks of various fish species have been eliminated and there are now thousands of lakes and rivers which are fishless or possess only degraded communities. The main problems are caused by engineering works, industrial and domestic pollution, acidification, fishing and fishery management, and land use practices. The major conservation objective, perhaps fortified by legislation, must be habitat restoration and management, but short-term programmes can usefully involve translocations, captive breeding and cryopreservation. Fish conservation programmes are needed in every country in order to rescue endangered species and reverse the downward trends facing important fish communities by managing the lake and river systems concerned.

A comparative study of water level regimes and littoral benthic communities in Scottish lochs

Abstract There has been little previous research on the impact of fluctuating water levels on the littoral communities of Scottish lochs. In 1980, 27 lochs were visited and the physical characteristics, macrophytes and zoobenthos of selected shores were studied. Long-term water level data were available for most of the lochs and these were used to divide them into three categories with (1) natural, (2) minor (i.e. less than 5 m fluctuation in the year preceding sampling), and (3) major fluctuations (i.e. more than 5 m fluctuation in the year preceding sampling). Examples of the weekly variations in water level changes over a year are given. The biological results were relatively clear. Though most of the shores studied had comparable substrates, the flora and fauna were linked with the type of water regime of the previous years. In the natural lochs and those with minor fluctuations in level, the littoral macrophytes and zoobenthos were usually varied and reasonably abundant, but in the lochs with major fluctuations the flora and fauna were very impoverished and sometimes completely absent. The critical level changes which cause this impoverishment are discussed and ways of ameliorating the problems are suggested.

The Ruffe Population of Loch Lomond, Scotland: Its Introduction, Population Expansion, and Interaction with Native Species

The ruffe (Gymnocephalus cernuus), never before recorded in Scotland, was discovered in Loch Lomond in 1982. During the 1980s ruffe became well established and expanded its range throughout the loch and through the slow-flowing influent and effluent tributaries, only being excluded from tributaries with high flow rates. Recoveries offish entrained at a pumping station, abstracting water for domestic supply, provide a measure of the rate of population expansion between 1982 and 1996 and the current status of ruffe in Loch Lomond. Between 1982 and 1992 the ruffe population grew exponentially. Since 1992 the population appears to have stabilized to some extent but at a very high level. Gill-netting surveys conducted throughout Loch Lomond have shown that the high abundance of ruffe recorded at this site is representative of a large population throughout the loch. The diet of ruffe feeding in Loch Lomond differed both spatially and seasonally. Although prey choice was diverse, it was primarily composed of benthic macro-invertebrates, but at times included underyearling fish (including ruffe) and eggs of other fish species. The most important of these is the powan (Coregonus lavaretus), a broadcast spawner of national conservation value. To examine the possibility of dietary overlap with perch (Perca fluviatilis) and brown trout (Salmo trutta), the diets of these three species were compared. The data showed very little evidence of overlap in diet, suggesting that feeding resource competition between ruffe and trout and ruffe and perch does not occur between adults of these species. Evidence for the disruption of predator-prey relations by introduced ruffe is reviewed. Ruffe are now the primary prey species for cormorants (Phalacrocorax carbo), herons (Ardea cinerea), and northern pike (Esox lucius) feeding in Loch Lomond. Calculations based on predator population sizes and consumption rates suggest that potentially up to 17 metric tons of ruffe, representing over 2 million individuals, may be being consumed annually by these predator species. The effects on native fish of this shift in diet in these predator species is discussed, as is the ability of ecologists to predict the impact of invasions of new species in aquatic communities.

Criteria for the selection of important sites for freshwater fish in the British isles

Abstract Factors relevant to the conservation of freshwater fish in the British Isles are reviewed. Many important fish sites are at present unprotected because of the absence of clear criteria on which to base selection. Criteria suggested and defined in this paper are rarity, local races, pristine stocks, unusual communities, community diversity and community type in relation to habitat. These criteria are discussed in detail and then presented in summary questionnaire form for the use of conservationists.

Notes on the biology of Gammarus pulex in the River Endrick

Summary1.Gammarus pulex is common in most parts of the River Endrick except the extreme upper and lower reaches. It appears to be most abundant under stones and weed where the current is moderate and where there are more than 4 mg of calcium per litre of river water.2.Breeding occurs from March to September, but ceases in the winter months.3.A specimen of Gammarus pulex with no eyes was found in a tributary of the River Endrick.4.The main predators of Gammarus pulex in the River Endrick appear to be fish, especially Salmo salar, Salmo trutta, Phoxinus phoxinus and Nemacheilus barbatula.Zusammenfassung1.Gammarus pulex findet sich gewöhnlich fast überall in dem Endrick Flusse, mit Ausnahme von der Quelle und der Mündung des Flusses. Die grösste Anzahl wird unter den Steinen und unter Unkraut gefunden, wo es keine zu starke Strömung gibt und wo es auch mehr als 4 mg Kalzium per Liter Wasser gibt.2.Die Fortpflanzung erfolgt von März bis September, aber hört während des Winters auf.3.Ein einziges augenloses Exemplar von Gammarus pulex wurde in einem Zuflusse des Endrick Flusses entdeckt.4.Es scheint, dass die wichtigsten Raubtiere von Gammarus pulex in dem Endrick Flusse Fische sind, besonders Salmo salar, Salmo trutta, Phoxinus phoxinus und Nemacheilus barbatula.

Ecology of Allis Shad Alosa alosa and Twaite Shad Alosa fallax in the Solway Firth, Scotland

The basis of this study were 132 adult Allis Shad and 150 Twaite Shad collected as bycatches from salmon stake nets in Scotland on the north side of the Solway Firth. Most (60%) of the Allis Shad were immature fish 2–3 years of age (mean length 305 mm). Mature males were younger (3–5 years) and smaller (mean length 421 mm) than females (4–6 years and 481 mm mean length). The largest Allis Shad was a female of 515 mm and 2183 g. In contrast, almost all the Twaite Shad were mature, the males younger (3–5 years) and smaller (mean length 341 mm) than the females (4–6 years and 364 mm mean length). The largest Twaite Shad was a female of 400 mm and 1213 g. The food of Allis Shad consisted mainly of small zooplankton with some fish and larger Crustacea. Fine vegetable fragments were common in the stomachs and attributed to filter feeding. The food of Twaite Shad was mainly small fish with some Crustacea. Mature Allis Shad of both sexes with large gonads (maximum female GSI: 20.63) were found throughout the spring and summer but no definite evidence of local spawning was obtained. Mature Twaite Shad of both sexes with large gonads (maximum female GSI: 23.32) were found until early July, thereafter most of the fish were spent. It appears that Twaite Shad spawn locally in June. Some hybrids between the two species were found.

The conservation of freshwater fishes in the British isles

Abstract This paper briefly reviews the status and distribution of populations of freshwater fishes in the British Isles and their worth as a resource. The total value of freshwater fishes to the community is far greater than is normally appreciated and includes, in addition to the economic sport and commercial fisheries, amenity, recreational, educational, and scientific, aspects as well as a potentially useful store of genetic material for the future. The main human pressures on existing fish stocks are discussed under the headings of fisheries, pollution, and land-used. The principal trends in the British Isles are away from natural and stable mixed fish populations towards artificially maintained, unstable stocks of a few species of sporting or commercial value. In particular the rarer, more sensitive, fish stocks with poor powers of distribution are being eradicated and replaced by commoner, more robust forms with greater powers of distribution. The rarer species and genetic strains can only survive if constructive conservation projects are initiated expeditiously at a variety of levels.

Future prospects for the freshwater fish fauna of the north Mediterranean region

Abstract The fresh waters of the north Mediterranean region possess a unique and diverse ichthyofauna with 229 endemic fish taxa in 13 families. With diverse threats to wetlands in the area and their increasing mismanagement many fishes are under threat and several taxa have become extinct in recent years. Following workshop discussions among specialists, a series of proposals is now put forward which is designed to reverse this trend. Within these proposals is the concept that clean water is desirable for both people and fish and that acceptable compromises must be the way to share this vital resource in the future. Managing water resources in the Mediterranean region is clearly going to be a key feature in the future development of this area and major issues must be resolved soon to avoid serious conflicts over water use in the 21st century.

Long-term trends in Loch Leven invertebrate communities

Detailed studies of the macroinvertebrate benthos and zooplankton communities in Loch Leven, the largest shallow lowland lake in Scotland, UK, were carried out from 1966 to 1973 as part of the International Biological Programme (IBP). The results revealed a reduction in species diversity that was attributed to increasing eutrophication. This work provides a baseline against which the response of the invertebrate communities to subsequent changes in management can be assessed. This article compares macroinvertebrate benthos and zooplankton data from the IBP study with the post-IBP era during which changes at Loch Leven included a 60% reduction in the phosphorus input from external sources and variations in fish stocking rates. Only in recent years has there been evidence of ecological recovery by the invertebrate communities: the number of macroinvertebrate and zooplankton taxa has increased (including taxa considered to be sensitive to nutrient enrichment) and invertebrate abundances have declined. These changes appear to reflect the improvements in water quality and habitat conditions at Loch Leven that have occurred as a result of the recent reduction in nutrient loads, albeit with a substantial delay before any ecological response could be detected. This time lag in recovery has important implications for assessing improvements in the ecological status of other lake systems, as is required by the EU Water Framework Directive.

Freshwater fish in Scotland in the 18th, 19th and 20th centuries

Abstract Information on the distribution of freshwater fish in Scotland, published in old accounts (particularly around 1790 and 1880 ), is compared with that of a recent survey (around 1970 ). Several changes are evident over the 180 years concerned, the main one being a northward extension of the distribution of a number of species, several apparently new to Scotland. Some of this dispersal is probably natural, but the main factor appears to be introduction by man — both from further south in Great Britain and from abroad. A number of unsuccessfull introductions of other species have been made. The future fish fauna of Scotland is discussed in the light of past and present events.