Conservation of freshwater fish in the British Isles: Proposals for management

1. Recent checklists of the freshwater fish of the British Isles have included 42 native and 13 introduced species. Of the former, however, two are extinct now and eight are threatened in various ways. In addition there are several important stocks of common native species under threat. 2. Protection for British fish exists mainly through legislation and protected sites of various designations. The legislation is inadequate in some respects and very few of the protected sites were actually established for their fish interest. Nevertheless, in Great Britain, 37 species of fish occur in National Nature Reserves. The overall status of fish in Sites of Special Scientific Interest is unknown. 3. The main conservation options for managing freshwater fish resources are habitat restoration, stock transfer to new sites, captive breeding and cryopreservation. The first two of these are regarded as the most useful for the long-term conservation of threatened species. Improved legislation would also help, especially in relation to preventing the import and transfer of potentially harmful species. 4. As well as the implementation of conservation management programmes for rare fish, research and monitoring studies are also needed in order to aid management and maintain a watch on populations of important species. In addition, national fish databases and registers of important stocks are an important background for overall fish conservation and management.     

Distribution and establishment of the alien Australian redclaw crayfish,Cherax quadricarinatus,in the Zambezi Basin

1. Crayfish are invasive polytrophic keystone species, which are phylogenetically unique on the African continent. The Australian redclaw crayfish Cherax quadricarinatus is invasive in southern African freshwater systems including the Zambezi River Basin. Surveys conducted across the Zambezi Basin (Botswana, Zimbabwe, Namibia and Zambia) between 2017 and 2019 showed that C. quadricarinatus is broadly distributed across the Upper and Middle Zambezi and is rapidly spreading through natural and human-mediated means across several ecoregions.
2. The probability of capture (P_capture), catch per unit effort (CPUE) and population characteristics of C. quadricarinatus from the recent Barotse floodplain invasion were compared with older invasions from Lake Kariba and Kafue River.
3. The P_capture and CPUE of C. quadricarinatus in the recently invaded region of the Barotse floodplain were similar to those of the older invasions. Mass and carapace length of C. quadricarinatus from the Barotse floodplain were significantly lower than those of C. quadricarinatus from the older invasions. Sex ratios differed significantly between the three invasive populations. The Barotse floodplain population had a disproportionate investment in females (65.3%) and intersex individuals (8.4%). No crayfish were detected in the Zambezian Headwaters or the Okavango Floodplains ecoregions, but current spread rates are 49 km yr⁻¹ downstream and 12 km yr⁻¹ upstream.
4. Investment in population management and the prevention of spread will have high conservation value across the invaded regions in order to restrict crayfish ecological impacts via direct predation and competition. In areas where crayfish are in high abundance, existing fisheries are affected through damage to nets, leading to increased net abandonment and ghost gear pollution in invaded regions.
5. The emphasis should be on developing cohesive transboundary biosecurity policies in southern Africa to limit further spread that will threaten the integrity of freshwater ecosystems. However, long-term monitoring is needed to gauge invasion risk to sensitive areas such as the Okavango Floodplains ecoregion and determine field-based ecological impacts.

     

The relationship between water quality and indigenous and alien crayfish distribution in the Czech Republic: patterns and conservation implications

相似文献   

Conservation of freshwater fish in the British Isles: the status of fish in national nature reserves

1. To consider fully the conservation management of freshwater fish, it was important to know which fish were already in the protected environment of National Nature Reserves (NNRs) — the principal sites for nature conservation in Great Britain. For this reason, 235 NNRs declared by the Nature Conservancy Council (NCC) were surveyed for freshwater fish between 1987 and 1990 by questionnaires to the wardens, by compiling data from other sources, and, where necessary, by field sampling. The presence of fresh waters (as lakes, ponds, rivers and streams) was also recorded. The survey was organized to follow the country and regional structure by which nature conservation was administered by the NCC so that the results could be considered accordingly. 2. Seventy five percent of NNRs contain fresh waters and, of these, just over 20% have no fish. Of the 51 fish species available 37 (73%) were recorded in NNRs. NCC regions with most fish species are: SW Scotland, West Midlands and East Anglia, but NW Scotland has the highest total of species occurrences in NNRs. In terms of both the numbers of species and their frequency of occurrence, NW and NE England are notably the lowest. The most common fish in NNRs are Eels, Brown Trout and Three-spined Sticklebacks. 3. The results for species and for sites (NNRs) are discussed from the viewpoint of fish conservation. The majority of fish in NNRs are those most common in Great Britain. Two of the species recorded (Powan and Smelt) are currently important for conservation, but several of those most threatened do not occur in NNRs. A number of NNRs have diverse fish communities, but only six have significant fish conservation value, of which Loch Lomond NNR is outstanding. 4. There is considerable scope through NNR management to improve fish conservation and it is suggested that the acquisition of new reserves for threatened species should be considered.     

Conserving the freshwater pearl mussel (Margaritifera margaritifera L.) in the British Isles and Continental europe

1. This paper reviews the status of the freshwater pearl mussel (Margaritifera margaritifera L.) in the British Isles and Continental Europe. 2. The mussel has continued to decline in recent decades throughout the European range, apparently caused mainly by pollution (especially by organic enrichment) and, in the British Isles, by a combination of this and overfishing for pearls. 3. Of particular concern is the almost complete absence of juveniles in most populations, with these occurring in numbers only in a very few rivers in remote locations. 4. M. margaritifera is now completely protected in most European countries and in Britain the government has recently made it an offence to kill or harm the mussel. However, it will still be permitted to take the mussel, examine it carefully for pearls, and then to return it unharmed to the river. This may prove difficult to enforce and it is concluded that it will be ineffective and that complete protection may still be needed. 5. There is no current monitoring programme for M. margaritifera anywhere in its range and without continuing evidence on its status and further research on the habitat requirements of the juveniles, it is difficult to be optimistic about its survival.     

Conservation of freshwater fish in the British Isles: The current status and biology of threatened species

1. The objective of this paper is to review the status of all freshwater fishes in the British Isles and to identify theatened species, races and communities which are in need of conservation. 2. Using objective criteria to assess the degree of threat, two of the 55 freshwater species known in the British Isles are thought to be extinct here and eight are believed to be under significant threat. 3. The biology of these ten species is reviewed. They are: Sturgeon Acipenser sturio, Allis Shad Alosa alosa, Twaite Shad Alosa fallax, Arctic Charr Salvelinus alpinus, Houting Coregonus oxyrinchus (extinct), Powan Coregonus lavaretus, Pollan Coregonus autumnalis, Vendace Coregonus albula, Smelt Osmerus eperlanus and Burbot Lota lota (extinct). 4. In addition, there are several races of commoner species which are believed to be worthy of special conservation measures. These fish include the purely freshwater race of River Lamprey Lampetra fluviatilis in Loch Lomond, dwarf Brook Lampreys Lampetra planeri in the Inner Hebrides, spineless Three-spined Sticklebacks Gasterosteus aculeatus in the Outer Hebrides and a number of important races of Brown Trout Salmo trutta in various waters in Ireland and Scotland. 5. There is also a range of fish communities in individual rivers and lakes which merit conservation attention. These are important for a variety of reasons, including high (and very low) diversity, unique assemblages, pristine stocks and highly characteristic communities. 6. The major threats to these species and communities include industrial and domestic pollution, acidification, land use changes, river barriers, drainage, fish farming, fishery management and the introduction of new species. 7. The identification of these threatened fishes and important freshwater sites provides a foundation for a review of existing protection in the British Isles and a major fish conservation management programme. These will be described in subsequent papers.     

Meat yields in the introduced freshwater crayfish, Pacifastacus leniusculus (Dana) and Astacus leptodactylus Eschscholtz, from British waters

The freshwater crayfish industry in Britain is based on two species, Pacifastacus leniusculus (Dana) and Astacus leptodactylus Eschscholtz, which were introduced during the 1970s and 1980s. The former is widely cultivated but both are also established in the wild, from where they are harvested. Very few studies have been made of the meat yield in these two species and none on British populations. Two essentially wild populations were assessed for their meat yield. Due to its more massive claws male P. leniusculus had a higher meat yield than male and female A. leptodactylus and female P. leniusculus in both winter and summer months. Less difference was found between the yield of tail meat between the sexes and species. Compared with other studies, meat yield in the two British populations of P. leniusculus (11–15%) and A. leptodactylus (9–13%) would appear to be lower; possible reasons for this are discussed. However, expressing meat yield as a percentage of wet body weight, although useful for comparative purposes, can give conflicting results – examples of this are given. Meat yields from the claws of the two species indicated that positive allometric growth continued after sexual maturity.     

The use of anglers' catches to monitor fish populations in large water bodies, with particular reference to the River Derwent, Derbyshire, England

Abstract. Nearly 2000 marked coarse fish of four species were introduced into a stretch in the middle reaches of the River Derwent. Derbyshire, England in an attempt to estimate the fish population size from catch returns. It was estimated that 800 dace, 1975 roach, 1481 chub and 366 bream were present in the reach and the density of the fish population (0·35 fish m^?2) was low. The validity of employing anglers as samplers in a mark-recapture exercise to estimate fish population size in large fisheries is discussed. Angler catch data were collected from angling clubs holding competitions on the Hoveringham Fishery on the lower reaches of the River Derwent over the period 1973/1974 to 1983/1984 to assess the impact of achange in management strategy on the fishery in 1979. Catch rates improved gradually until 1979/1980 when a dramatic increase occurred. This elevated catch rate, in excess of 400 g man-h^?1, was maintained and, in recent years, further enhanced (>500 g man-h^?1). The improvement was the result of a strong year-class of chub entering the catchable cohort and dominating anglers' catches and not the change in management policy.     

Effects of dietary protein level on muscle cellularity and flesh quality in Atlantic salmon with particular reference to gaping

Growth performance, muscle cellularity and flesh quality were investigated in Atlantic salmon (Salmo salar L.) fed either of two diet ranges [high protein (HP), or low protein (LP)], which differed in digestible protein/digestible energy ratios but were of equivalent digestible energy content (21.4 MJ kg⁻¹ wet weight). Smolts from an early maturing (Lochy) and a late maturing (Mowi) strain were PIT-tagged and reared together in duplicate 5×5×5-m sea cages for each diet. The Lochy and Mowi fish were harvested in May and August, respectively, after 417 and 515 days in seawater. The average body weight of fish in each cage at harvest was in the range 3.8–5.4 kg, with no significant difference between diets. The total cross-sectional area of white muscle and the number and diameter of muscle fibres was determined at the level of the first dorsal fin ray. The distribution of muscle fibre diameters was investigated using nonparametric smoothing and bootstrapping techniques. Diet had no effect on fibre size distribution or fibre number in the Mowi strain, and small but significant effects for the Lochy strain. At harvest, in Lochy salmon of average fork length 69 cm there were around 15% more fibres in fish fed the HP than LP ratio diets. However, the 50th percentile of fibre diameter was 20% greater in fish fed the LP than HP diets, such that the total muscle cross-sectional area was similar. The lipid content (14.1–15.3% wet mass), astaxanthin pigment concentration (7.0–8.5 mg kg⁻¹ wet mass) and colour (RocheSalmoFan™ and Minolta Chromatometer readings) of the flesh were similar for both strains and diets. There was no significant difference in the average muscle fibre density between strains and diet, which varied between 60 and 140 fibres mm⁻² muscle cross-sectional area. Gaping during processing of the fillet was in part related to muscle cellularity. Little or no gaping was observed in any fish with a fibre density in excess of 95 fibres mm⁻² muscle. It was concluded that individual variation in fibre density is important in the development of gaping, but that muscle cellularity and flesh quality are relatively insensitive to the protein to energy ratio in the diet over the range studied.     

Effects of temperature and water calcium concentration on growth,survival and moulting of freshwater crayfish,Paranephrops zealandicus

Two 3-month experiments were conducted to investigate the effects of temperature and water calcium concentrations on growth, survival and moulting of freshwater crayfish (Paranephrops zealandicus). Both experiments were conducted using three replicates of five treatments (water temperatures of 14, 16, 18, 20 and 22 °C for Experiment 1 and water calcium concentrations of 0, 5, 10, 30 and 80 mg/L for Experiment 2). Growth rates increased with water temperature (maximum specific growth rate = 0.57) but were unchanged with increased water calcium concentration. Variability in growth rates decreased with increased water calcium concentrations. Survival decreased as water temperatures exceeded 16 °C and increased with water calcium concentrations above 10 mg/L. Inter-moult period decreased from > 90 ± 20 days at water temperatures of 14 °C to ∼ 40 ± 10 days at water temperatures > 20 °C. Moult increment of the crayfish was unaltered by either water temperature or water calcium concentrations. The optimum water temperature for productivity under conditions employed was 16 °C.     

Incisor ridge modification of the mandibles in freshwater crayfish, Astacus leptodactylus

The differences in the ridge structure of the mandibles of different size Astacus leptodactylus (32–80 mm carapace length, CL) were investigated. The results showed that a modification occurs with an increase in size in the incisor ridge of mandibles in A. leptodactylus. The results also showed that A. leptodactylus possesses four different types of ridge structure in the mandibles. These are: (1) Incisor ridge with big teeth (dentate crenate), (2) Blade-like incisor ridge with numerous small teeth, (3) Blade-like ridge (toothless), (4) Blunt ridge. In conclusion, it is thought that the incisor ridge modification of the mandibles may cause the difference in the food choice of different size A. leptodactylus, because, crayfish possessing different ridge structures of the mandible may probably feed on different type of food.     

Non-specific defence mechanisms in fish, with particular reference to the reticuloendothelial system (RES)

An efficient clearance and degradation system may be needed during microbial invasion which otherwise would lead to severe inflammation and eventually death. Non-specific defence mechanisms in fish play an important role at all stages in infection. The non-specific humoral defence including proteases, lysins and agglutinins, for example, in mucosal secretion is the first line of defence, whereas mucosal lining cells function as the second barrier against invasion. Blood cells, especially granulocytes and monocytes, may destroy microbes present in the circulation and may function as the third line of defence. Finally, endocytically active cells such as endothelial cells, macrophages and granulocytes in organs and tissues may take up and degrade microbes or microbial products. The endocytic and degradation processes strongly depend on the effectiveness of the reticuloendothelial system which consists of endothelial cells and macrophages that line small blood vessels (e.g. sinusoids and ellipsoids). Potentiation of non-specific defence mechanisms may occur during microbial invasion, leading to more efficient clearance and destruction of pathogens or other harmful substances. In microbial invasion, an inflammatory response such as elevated production of antimicrobial substances is often encountered. Central cells in the production of antimicrobial substances are macrophages and granulocytes, and microbial products in inflammation may alter the cells function to a more activated state in vivo. Activated cells may enhance their antimicrobial capacity and efficiency by producing higher amounts and more active antimicrobial agents. This review concerns the non-specific defence system and gives an introduction to some of the known non-specific humoral substances and their induction/suppression, and provides a more extensive introduction to cytokine research and immunomodulation. Cellular aspects of non-specific defence, including macrophages and their products, are discussed in the light of their function in the reticuloendothelial system in fish.     

Distribution and feeding of juvenile Pacific salmon in freshwater tidal creeks of the lower Fraser River, British Columbia

Abstract This study examined juvenile salmonid use of a freshwater tidal creek system draining a wetland on the floodplain of the lower Fraser River, British Columbia, Canada. Chum, Oncorhynchus keta (Walbaum), chinook, O. tshawytscha (Walbaum), and sockeye, O. nerka (Walbaum), salmon fry were abundant in the tidal creeks in spring. The fry were found in non-natal habitat up to 1.5 km from the main channel of the river. The salmon fry ate dipteran adults, larvae and pupae, cyclopoid and harpacticoid copepods, and Collembola. Mysids Neomysis mercedis Holmes (Walbaum), and amphipods, Crangonyx richmondensis occidentalis (Hubricht and Harrison), were also consumed. The upper reaches of an undisturbed creek were the winter rearing habitat for presmolt coho salmon, O. kisutch (Walbaum), where this species ate dipteran pupae and larvae as well as a freshwater isopod, Asellus communis Say (Walbaum).     

Genetic implications of translocation and stocking of fish species, with particular reference to Western Australia

Species or strains of fish may be translocated for farming, where the only access to the wild is via inadvertent escapes, or for stocking, where deliberate releases are undertaken. In either case, it is important that the translocated animals are representative of the donor population(s) in terms of genetic composition and level of variability. Many studies have shown that this ideal is difficult to achieve, the major reason being the use of inadequate numbers or composition of broodstock as founders of a strain. Also, where more than one conspecific population is involved, there may be outbreeding depression problems. In the case of farming, measures to improve the introduced strain genetically are likely to be undertaken, e.g. breeding programmes, manipulation of sex and ploidy, transgenic techniques. Such approaches are necessary economically, but can alter genetic make‐up. Thus, stringent attempts must be made to minimize escapes or reduce their impact should they occur. With stocking, genetic change during captive rearing should be avoided. No strain manipulation should be undertaken, and other agents of change should be minimized. Stocking may result in hybridization with related species or with endemic populations of the same species. In either case, there can be detrimental genetic effects on the native forms. To be able to identify subsequently any genetic changes in reared strains, whether intended for farming or stocking, wild population composition should be determined, using appropriate molecular techniques. Such molecular methods will demonstrate the degree of interpopulation differentiation and, thus, reproductive isolation. The same markers should then be used in each subsequent generation (in the hatchery and after escape or reintroduction to the wild) to monitor any changes in genetic composition or variability. Markers should include microsatellite DNA loci, but the inclusion of more than one type of marker is recommended. However, as the aforementioned markers are not considered to be influenced by natural selection, they give no information on the adaptive nature of such differences. For this reason, it is suggested that markers influenced by selection should be investigated. Monitoring a strain subsequent to deliberate or inadvertent release can be undertaken using genetic markers, either deliberately enhanced by breeding or occurring naturally. Highly variable minisatellite DNA loci have been used as family markers in farmed escape studies with Atlantic salmon. These investigations have demonstrated significantly superior survival of native strains compared with farmed salmon in natural stream conditions. These latter results, demonstrating fitness differences, were strongly indicative of local adaptation. Thus, methods exist to monitor the genetic effects of translocation and stocking. However, a holistic approach should be taken to such exercises, where genetics forms part of a wider suite of considerations.     

The harvest of the freshwater crayfish <Emphasis Type="Italic">Astacus leptodactylus</Emphasis> Eschscholtz in Turkey: harvest history,impact of crayfish plague,and present distribution of harvested populations

This review focuses on the present distribution of populations of the crayfish Astacus leptodactylus that are harvested in Turkey. It also examines the history of this harvest and the impact that crayfish plague has had on them. Crayfish plague, caused by the fungus-like organism, Aphanomyces astaci Schikora, 1906, is a severe parasite of freshwater crayfish and has caused a lot of damage to A. leptodactylus populations in Turkey since 1984. Turkey was the largest provider of A. leptodactylus to Western Europe from 1970 (or possibly earlier) until 1986. For example, the peak production was reached in the early 1980s, with over 5,000 tonnes being exported in 1984. On the other hand, as a result of the crayfish plague the harvest of A. leptodactylus was reduced severely in most populations in Turkey after 1985. The harvest was only 320 tonnes in 1991. After the occurrence of crayfish plague in Turkey, in order to increase crayfish production uncontrolled A. leptodactylus stockings have been carried out in many waterbodies throughout Turkey. These introductions have caused an increase in the number of A. leptodactylus populations, but exploitation of A. leptodactylus is still under the pressure of the plague, although there has been a steady increase in crayfish production in recent years. The harvest increased to 2,317 tonnes in 2004. Fortunately, among those populations affected by crayfish plague, large amounts of A. leptodactylus can still be harvested from three lakes, ?znik (Bursa), E?irdir (Isparta) and Çivril (Denizli). Thus, it seems that A. leptodactylus has a degree of resistance to crayfish plague. It is therefore interesting to investigate the resistance of A. leptodactylus caught from these populations to crayfish plague.     

Inheritance of molecular markers and sex in the Australian freshwater crayfish, Cherax destructor Clark

Inheritance of three kinds of molecular genetic markers (mtDNA, random‐amplified polymorphic DNAs (RAPDs) and allozymes) and sex were investigated in crossbreeding experiments between three populations of the Australian freshwater crayfish Cherax destructor. Crossbreeding did not disrupt the ively maternally inherited, and allozyme and RAPD markers were transmitted following expected Mendelian principles for co‐dominant and dominant traits respectively. Unlike these three markers, sex ratios were found to be distorted by crossbreeding in some families. Two crossbred families produced only females. The implications of these findings for freshwater crayfish population genetics, taxonomy and aquaculture are discussed.     

Aspects of the population genetics of herring,Clupea harengus,around the British Isles and in the Baltic Sea

Electrophoretic variation within and among Clupea harengus L. samples taken from 10 locations in the northwest region of the British Isles and from a spawning site in the Baltic Sea and Thames Estuary were studied. Sixteen enzyme systems, coded by a putative 30 loci, were examined. Twelve loci were found to be polymorphic and were considered usable for population surveys. The proportion of polymorphic loci varied between 0.115 and 0.230 (0.95 criterion) and between 0.308 and 0.461 (0.99 criterion); average heterozygosity was 0.045 ± 0.02. Differentiation among samples was found to be low, even between samples from the west of Ireland and the Baltic Sea. The average Nei's genetic distance was 0.0004 and F_ST value was 0.002. The magnitude of genetic differentiation between stocks, as indicated from genetic distance values, is within a much narrower range than found between geographically isolated populations of other fish species. Temporal stability over three different development stages and eight overlapping year classes of North Irish Sea herring was demonstrated.     

Mating and spawning of freshwater crayfish, Austropotamobius pallipes Lereboullet, under laboratory conditions

Abstract. The study includes mating and spawning data of freshwater crayfish, Austropotamobius pallipes Lereboullet, obtained in four consecutive years (1987–1990). A total number of 586 wild-caught female A. pallipes in the 21·65 mm to 45·60mm carapace length (CL) size were held under laboratory conditions at different dates in September–October. Initial densities at mating time were 21 and 24 crayfish/m² with a 1:2 male:female ratio. High percentages of mating were obtained (97·4–100%) except in 1989 (57·5%). In all years, most of the matings (90%) were concentrated in a period of 8–12 days with mean water temperatures between 12°C and 13·5°C. Spawning took place a few days after mating (minimum 2 days, maximum 14 days) at mean water temperatures between 8·2°C and 10·8°C. In the first 3 years, almost 100% of mated females spawned. However, in the fourth year (1990), when the mean size of crayfish was smaller, only 72·4% of mated females spawned. The mean number of pleopodal eggs was 64 (maximum 220, minimum 18). Egg diameter ranged between 2·30 and 3·25 mm (mean value 2·78 mm). Pleopodal egg number was positively correlated with carapace length ( r = 0·72).