An alternative to dolphin oil as a fish attractant in the Ganges River system: conservation of the Ganges River dolphin

Oil extracted from blubber of the Ganges River dolphin, Platanista gangetica, is used as a fish attractant in India and Bangladesh. This oil fishery is associated with the mortality of hundreds of dolphins every year. Oil from fish scraps was field tested for 121 days during 1997-1999 in the Ganges at Patna and was a very effective alternative to dolphin oil as a fish attractant. Fishing with fish oil resulted in higher catches and greater income per person per hour (Rs. 17.8±12.5) than fishing with dolphin oil (Rs. 11.6±9.3). However, there is no statistically significant difference between the results from fishing with dolphin and fish oil. Oil from fish scraps is inexpensive and can be made readily available to all the fishermen. Its widespread use would help in conserving the endangered Ganges River dolphin.     

Site fidelity and along-shore range in Hector's dolphin, an endangered marine dolphin from New Zealand

To document site fidelity and the alongshore range of individual Hector's dolphins we analysed sightings of 32 photographically identified dolphins, each seen ?10 times at Banks Peninsula, New Zealand, between 1985 and 1997. The furthest two sightings of an individual were 106 km apart. All other individuals ranged over less than 60 km (x?=31.0 km, SE=2.43) of coastline. Gender did not significantly influence alongshore range (female x?=30.4 km, SE =3.21, n=18; male x?=27.4 km, SE=5.68, n=5). Site fidelity was high: for example, on average, individuals were seen in Akaroa Harbour for about two thirds of the years they were known to be alive. These data suggest that impacts on Hector's dolphins are most appropriately managed on a small spatial scale.     

Surface water and ground-water thresholds for maintaining Populus-Salix forests, San Pedro River, Arizona

Ground-water and surface flow depletions are altering riparian ecosystems throughout the southwestern United States, and have contributed to the decline of forests of the pioneer trees Populus fremontii (Fremont cottonwood) and Salix gooddingii (Goodding willow). On some rivers, these forests have been replaced by shrublands of Tamarix ramosissima (tamarisk), a drought-tolerant species from Eurasia. The physiological response of these three riparian plant species to decreases in water availability is well studied, but little attention has been given to shifts in community and population structure in response to declines in surface flow and ground-water levels. Based on study of 17 sites spanning a hydrologic gradient, this research identified hydrologic thresholds above which P. fremontii-S. gooddingii maintain tall dense stands with diverse age classes, and above which they are more abundant than T. ramosissima stands along the San Pedro River in Arizona. Surface flow permanence was the hydrologic variable that explained most of the variance in species abundance and relative importance, with inter-annual ground-water fluctuation and depth to ground water also contributing. P. fremontii and S. gooddingii were dominant over T. ramosissima at sites where surface flow was present more than 76% of the time, inter-annual ground-water fluctuation was less than 0.5 m, and average maximum depth to ground water was less than 2.6 m, during a two-year period of data collection. Because T. ramosissima is a shrub species with smaller leaves and lower canopy heights than P. fremontii and S. gooddingii, these shifts in species composition corresponded to decreases in maximum canopy height and upper stratum (above 8 m) vegetation volume as site water availability declined. As well, sites with deeper water tables and more intermittent flows had greater areal coverage of shrublands and less of woodlands. The altered vegetation structure along dewatered rivers may lower wildlife habitat quality. This study provides river managers with quantitative hydrologic guidelines for conserving tall dense P. fremontii-S. gooddingii stands and emphasizes the importance of maintaining long-term hydrologic conditions that are favorable to these species. The study also has implications for riparian restoration and invasive species management by suggesting that desired outcomes may be achieved through restoration of physical processes.     

Status and recent trends of the great bustard (Otis tarda) population in the Iberian peninsula

We present an updated estimate of the great bustard population in the Iberian peninsula. The sum of the most recent counts was 20,243, and the estimated total, 24,490 birds. During the last two decades bustards increased at five intensive study areas, remained stable at two, and declined or became extinct at eight. These population changes were determined by both variations in breeding success at each area and migration of birds between areas. Our results suggest that the population is probably concentrating at high quality areas, and disappearing from poor quality ones. We also identified 29 areas where bustards have become extinct during the last four decades, mostly due to hunting and agricultural transformations. In conclusion, although the population is apparently not decreasing at present, the concentration trend described could lead to a higher species’ vulnerability, a loss of genetic diversity, and a further isolation of marginal groups. Strict conservation measures should thus be directed at preventing the decrease of the number of extant leks.     

Interaction between the soil yeast Rhodotorula mucilaginosa and the arbuscular mycorrhizal fungi Glomus mosseae and Gigaspora rosea

The effect of the soil yeast, Rhodotorula mucilaginosa LBA, on Glomus mosseae (BEG n°12) and Gigaspora rosea (BEG n°9) was studied in vitro and in greenhouse trials. Hyphal length of G. mosseae and G. rosea spores increased significantly in the presence of R. mucilaginosa. Exudates from R. mucilaginosa stimulated hyphal growth of G. mosseae and G. rosea spores. Increase in hyphal length of G. mosseae coincided with an increase in R. mucilaginosa exudates. No stimulation of G. rosea hyphal growth was detected when 0.3 and 0.5 ml per petri dish of yeast exudates was applied. Percentage root length colonization by G. mosseae in soybean (Glycine max L. Merill) and by G. rosea in red clover (Trifolium pratense L. cv. Huia) was increased only when the soil yeast was inoculated before G. mosseae or G. rosea was introduced. Beneficial effects of R. mucilaginosa on arbuscular mycorrhizal (AM) colonization were found when the soil yeast was inoculated either as a thin agar slice or as a volume of 5 and 10 ml of an aqueous solution. R. mucilaginosa exudates (20 ml per pots) applied to soil increased significantly the percentage of AM colonization of soybean and red clover.     

Non-pathogenic Fusarium strains protect the seedlings of Lepidium sativum from Pythium ultimum

Two root-colonizing Fusarium strains, Ls-F-in-4-1 and Rs-F-in-11, isolated from roots of Brassicaceae plants, induced the resistance in Lepidium sativum seedlings against Pythium ultimum. These strains caused an increase in the content of benzyl isothiocyanate, and of its precursor glucotropaeolin, in the roots of the host plants. The increased isothiocyanate content is one of the factors contributing to the resistance of L. sativum against P. ultimum. To be transformed into the fungitoxic compound benzyl isothiocyanate, glucotropaeolin has to be hydrolyzed by myrosinase, which can be produced either by plants or microorganisms. The Fusarium strain Ls-F-in-4-1 has a myrosinase activity but the strain Rs-F-in-11 has not. These results suggest that both strains are able to trigger the metabolic pathway leading to benzyl isothiocyanate production in the plant. In the case of the myrosinase-negative strain Rs-F-in-11, hydrolyzation into isothiocyanate is only due to the myrosinase activity of the plant, and in the other case, the myrosinase produced by the strain Ls-F-in-11 also would contribute to the production of isothiocyanate. This paper reports a new mode of action of non-pathogenic Fusarium strains in controlling P. ultimum.     

Distribution, status, and conservation needs of the golden-crowned sifaka (Propithecus tattersalli)

The golden-crowned sifaka is considered one of the world's most endangered primates. To evaluate the species' current conservation status we established its actual distribution and abundance, and assessed current threats that affect its survival. Study methods involved direct sifaka observations and interviews to local villagers. Propithecus tattersalli's distribution is restricted to the region comprised between the Loky and Manambato rivers. Throughout its range, the species is abundant and it can even be found in small forest fragments, although it was never observed at elevations above 700 m.a.s.l. Major threats to the species include habitat destruction through slash-and-burn agriculture, grass fires, wood and gold extraction, and poaching. Total population estimates range from 6100 to 10,000 individuals, with an effective population size of approximately 2500-4000 sifakas. Though sensitive to forest destruction, the species seems to be resilient to current levels of landscape fragmentation. We recommend the establishment of a system of protected areas throughout the Loky-Manambato region and the implementation of a “Flagship Species Program” utilizing the golden-crowned sifaka as a catalyst for a regional Conservation Management Plan.     

Quantification of Wautersia [Ralstonia] basilensis in the mycorrhizosphere of Pinus thunbergii Parl. and its effect on mycorrhizal formation

The bacterium Wautersia [Ralstonia] basilensis has been shown to enhance the mycorrhizal symbiosis between Suillus granulatus and Pinus thunbergii (Japanese black pine). However, no information is available about this bacterium under field conditions. The objectives of this study were to detect W. basilensis in bulk and mycorhizosphere soils in a Japanese pine plantation in the Tottori Sand Dunes, determine the density of W. basilensis in soil, and determine the optimal cell density of W. basilensis for mycorrhizal formation in pine seedlings. We designed and validated 16S rRNA gene-targeted specific primers for detection and quantification of W. basilensis. SYBR Green I real-time PCR assay was used. A standard curve relating cultured W. basilensis cell density (10³-10⁸ cells ml⁻¹) to amplification of DNA showed a strong linear relationship (R = 0.9968). The specificity of the reaction was confirmed by analyzing DNA melting curves and sequencing of the amplicon. The average cell density of W. basilensis was >4.8 × 10⁷ cells g⁻¹ of soil in the mycorrhizosphere and 7.0 × 10⁶ cells g⁻¹ in the bulk soil. We evaluated the W. basilensis cell density required for mycorrhizal formation using an in vitro microcosm with various inoculum densities ranging from 10² to 10⁷ cells g⁻¹ soil (10⁴-10⁹ cells ml⁻¹). Cell densities of W. basilensis of >10⁶ cells g⁻¹ of soil were required to stimulate mycorrhizal formation. In vivo and in vitro experiments showed that W. basilensis was sufficiently abundant to enhance mycorrhizal formation in the mycorrhizosphere of Japanese black pine sampled from the Tottori Sand Dunes.     

Extirpation and reintroduction of fishers (Martes pennanti) in Oregon: implications for their conservation in the Pacific states

Prior to extensive European settlement, the fisher (Martes pennanti) occupied most coniferous forest habitats in Washington, Oregon, and California. Human activities since that time have resulted in the apparent extirpation of fishers throughout much of their historical range in the Pacific states. Fisher extirpations in California and Washington have been documented previously, but no comprehensive assessments of the distribution of fishers in Oregon, the history of their translocation into Oregon, or the conservation of fishers in the Pacific states have been conducted. Our objectives are to (1) review historical information on potential causes for fisher population losses in Oregon, (2) document the history of their translocation into Oregon, (3) describe the distribution of fishers in Oregon relative to those translocations and determine if any were successful, and (4) discuss the implications of our findings for the conservation of fishers in the Pacific states. Our results show that extant populations of fishers in Oregon are restricted to two disjunct and genetically isolated populations in the southwestern portion of the state: one in the southern Cascade Range and one in the northern Siskiyou Mountains. In addition, historical changes in the distribution of fisher occurrence records in Oregon and geographic variation in the genetic composition and size of fishers occurring in southwestern Oregon, show that the population in the southern Cascade Range is reintroduced and is descended from fishers that were translocated to Oregon from British Columbia and Minnesota. The loss of fisher populations from central and northern Oregon and throughout Washington has resulted in the isolation of extant populations in Oregon by >650 km from those occurring in southern British Columbia. Our results demonstrate that the historical continuity in fisher distribution that once provided for genetic interchange among fisher populations in the Pacific states no longer exists.     

Effects of Medicago sativa, Taraxacum officinale and Bromus sterilis on the density and diversity of Collembola in grassy arable fallows of different ages

The density and diversity of Collembola of nine grassy arable fallows of different ages were investigated in a factorial design with the factors ‘plant species’ (legume: Medicago sativa, herb: Taraxacum officinale, grass: Bromus sterilis) and ‘age class’ (2-3, 6-8 and 12-15 years) including the random effect ‘site’ (1-9). In May 2008, four plots were selected randomly at each fallow. Within each plot five M. sativa, T. officinale and B. sterilis plants were extracted with their associated soil using steel cylinders. The material from each plant species was used for extraction of Collembola and for determination of environmental parameters. Thus, the new aspect of the present study compared to other field studies investigating the relationships between plant and Collembolan communities is the focus on the “micro-scale”, investigating the Collembolan communities of the soil associated with single plants.We found that species richness and density of total and euedaphic Collembola were significantly higher in B. sterilis than in T. officinale samples with the M. sativa samples being intermediate. Fine-root feeding euedaphic Collembola particularly benefited from the higher amount of fine roots in B. sterilis samples. We also discovered that the age of the fallows had no significant influence on the number of Collembolan species and the density of the Collembolan groups. Notably, however, species of the epedaphic genera Lepidocyrtus and Sminthurinus were associated with the 12-15 year-old fallows and presumably benefited from the high number of plant species in the old fallows. Finally, canonical correspondence analysis (CCA) indicated that the soil organic matter content and the microbial biomass, both potential food sources for many Collembolan species, were important structuring forces for the Collembolan communities.     

Inferring species distributions in the absence of occurrence records: An example considering wolverine (Gulo gulo) and Canada lynx (Lynx canadensis) in New Mexico

Information about geographic distributions is required for species conservation and management. Ultimately, this information is derived from records of occurrence. However, the reliability and availability of occurrence records are variable. A conceptual framework for evaluating the reliability of occurrence records is provided. Only records associated with physical evidence, especially a museum voucher specimen, are considered verified. However, errors in species identification or location are possible even for verified records. In addition, biases exist in occurrence records because they generally are collected haphazardly. Other sources of bias include sampling error associated with small areas or range limits and aspects of the species’ biology that make it unlikely to be documented. A practical method is provided for interpreting a species’ distribution in a particular area given a paucity of reliable occurrence records. Factors that must be considered for including such areas of interest within the range of a species include: (1) plausible reason for the paucity of records; (2) continuous suitable habitat between the area of interest and localities of reliable occurrence; and (3) absence of biogeographic breaks in the distribution of other organisms with similar evolutionary histories. The possible distribution of wolverine (Gulo gulo) and Canada lynx (Lynx canadensis) in New Mexico provides a case study of this approach. It is concluded that the mountains of north-central New Mexico should be considered within the natural range of wolverine and Canada lynx.     

Status and conservation of the grey seal, Halichœrus grypus, in France

We investigated the status of the grey seal in the Molène archipelago, western Brittany, where a Marine National Park is planned. We combined regular censuses, photo-identification and satellite telemetry to investigate trends in grey seal abundance, site fidelity, individual movements and haulout site use. Individual movements and seasonal variations in abundance suggest that the seals used the Molène archipelago alternatively with other haulout sites of the South-west British Isles during their annual cycle. Nine out of 16 seals fitted with Satellite Relay Data Loggers (SRDLs) moved to the Isles of Scilly, English Cornwall, Wales or the Channel islands. On average the seals spent 85% of their time Near Haulout, 56.8% of which in the Molène archipelago. Overall the seals spent 66% of their tracking time within the boundaries of the Marine National Park. From 1997 to 2000 in the Molène archipelago, we observed a peak in number during the moulting season (mean = 49.8 seals) and a lower abundance during the breeding season (mean = 38.3 seals). The sex ratio was strongly skewed towards males during the moult (between 3.1 and 5.3-1), and was close to 1:1 during the summer. Inter-annual site fidelity outside the breeding season was very high, varying from 70% to 95% of identified seals, suggesting that the observed movements constitute rotations rather than random dispersion. From 1991/1994 to 1997/2000, the mean number of seals counted at haulout sites increased by 7%, close to the rates of increase observed in the core population of the British Isles at the same period. The Marine National Park may be too restricted for the overall conservation of the population but management plans should be aimed at preserving the characteristics of the habitat for the grey seal.     

Lotononis angolensis forms nitrogen fixing, lupinoid nodules with phylogenetically unique, fast-growing, pink-pigmented bacteria, which do not nodulate L. bainesii or L. listii

Root-nodule bacteria that nodulate the legume genus Lotononis are being investigated to develop new forage species for agriculture. Bacteria isolated from nodules of Lotononis angolensis were fast-growing, highly mucoid and pink-pigmented, and on the basis of 16S rRNA phylogeny <94% related to other genera in the Alphaproteobacteria. Root-nodule bacteria isolated from other Lotononis species (L. bainesii, L. solitudinis and L. listii) resembled the more common dry, slow-growing, pink-pigmented rhizobia previously described for L. bainesii. These isolates could be attributed to the Methylobacterium genus, although not to the type species Methylobacterium nodulans. Further differences were uncovered with nodulation studies revealing that nodule isolates from L. angolensis were effective at nitrogen fixation on their host plant, but could nodulate neither L. bainesii nor L. listii. Reciprocal tests showed isolates from L. bainesii, L. listii and L. solitudinis were incapable of nodulating L. angolensis effectively. Nodule morphology for L. bainesii, L. angolensis and L. listii was characteristically lupinoid, with little structural divergence between the species, and with nodules eventually enclosing the entire root.     

Rapid identification and discrimination among Egyptian genotypes of Rhizobium leguminosarum bv. viciae and Sinorhizobium meliloti nodulating faba bean (Vicia faba L.) by analysis of nodC, ARDRA, and rDNA sequence analysis

Twenty-eight Rhizobium strains were isolated from the root nodules of faba bean (Vicia faba L.) collected from 11 governorates in Egypt. A majority of these strains (57%) were identified as Rhizobium leguminosarum bv. viciae (Rlv) based on analysis of a nodC gene fragment amplified using specific primers for these faba bean symbionts. The strains were characterized using a polyphasic approach, including nodulation pattern, tolerance to environmental stresses, and genetic diversity based on amplified ribosomal DNA-restriction analysis (ARDRA) of both 16S and 23S rDNA. Analysis of tolerance to environmental stresses revealed that some of these strains can survive in the presence of 1% NaCl and a majority of them survived well at 37 °C. ARDRA indicated that the strains could be divided into six 16S rDNA genotypes and five 23S rDNA genotypes. Sequence analysis of 16S rDNA indicated that 57% were Rlv, two strains were Rhizobium etli, one strain was taxonomically related to Rhizobium rubi, and a group of strains were most closely related to Sinorhizobium meliloti. Results of these studies indicate that genetically diverse rhizobial strains are capable of forming N₂-fixing symbiotic associations with faba bean and PCR done using nodC primers allows for the rapid identification of V. faba symbionts.     

Pre-symbiotic and symbiotic interactions between Glomus intraradices and two Paenibacillus species isolated from AM propagules. In vitro and in vivo assays with soybean (AG043RG) as plant host

Two indole-producing Paenibacillus species, known to be associated with propagules of arbuscular mycorrhizal (AM) fungi, were examined for their mycorrhization helper bacteria activity at pre-symbiotic and symbiotic stages of the AM association. The effects were tested under in vitro and in vivo conditions using an axenically propagated strain of the AM fungus Glomus intraradices and Glycine max (soybean) as the plant host. The rates of spore germination and re-growth of intraradical mycelium were not affected by inoculation with Paenibacillus strains in spite of the variation of indole production measured in the bacterial supernatants. However, a significant promotion in pre-symbiotic mycelium development occurred after inoculation of both bacteria under in vitro conditions. The Paenibacillus rhizosphaerae strain TGX5E significantly increased the extraradical mycelium network, the rates of sporulation, and root colonization in the in vitro symbiotic association. These results were also observed in the rhizosphere of soybean plants grown under greenhouse conditions, when P. rhizosphaerae was co-inoculated with G. intraradices. However, soybean dry biomass production was not associated with the increased development and infectivity values of G. intraradices. Paenibacillus favisporus strain TG1R2 caused suppression of the parameters evaluated for G. intraradices during in vitro symbiotic stages, but not under in vivo conditions. The extraradical mycelium network produced and the colonization of soybean roots by G. intraradices were promoted compared to the control treatments. In addition, dual inoculation had a promoting effect on soybean biomass production. In summary, species of Paenibacillus associated with AM fungus structures in the soil, may have a promoting effect on short term pre-symbiotic mycelium development, and little impact on AM propagule germination. These findings could explain the associations found between some bacterial strains and AM fungus propagules.     

Sampling on private property to evaluate population status and effects of land use practices on the gopher tortoise, Gopherus polyphemus

Although private properties are predicted to play an increasingly significant role in conservation, surveys of species of special concern are rare on these lands. We created a template for a multi-county survey of randomly selected sites and sampled for burrows of the gopher tortoise (Gopherus polyphemus) in south-central Georgia, USA. Current land use was strongly correlated with tortoise population condition. The highest densities of tortoise burrows were found on lands with open-canopied pine stands that were managed with prescribed fire, a practice associated with types of selection forestry and/or wildlife management. Agricultural sites and unburned areas provided poor habitat and pine plantations were only slightly better. Our estimates of tortoise population densities indicated that the current landscape supports less than 20% of the animals present before implementation of modern land use practices. In addition, our estimate for density of active burrows was approximately one third of that projected for the entire state range 20 years ago by Auffenberg and Franz [Auffenberg, W., Franz, R., 1982. The status and distribution of the gopher tortoise (Gopherus polyphemus). In: Bury, R.B. (Ed.), North American Tortoises: Conservation and Ecology (US Fish and Wildlife Service Wildlife Research Report 12). pp. 95-126]. However, some good sites for gopher tortoises remain in south Georgia and our data also suggested that extraordinary conservation actions may not be required if ways can be developed to retain traditional land management practices on private property.     

Distribution, status, and conservation of radiated tortoises (Geochelone radiata) in Madagascar

The radiated tortoise, Geochelone radiata, one of Madagascar’s four endemic tortoises, occupies a narrow band of xeric spiny forest along the island’s southwest coast. Traditionally avoided by indigenous tribes, these tortoises are now routinely harvested for food. An accurate assessment of human exploitation remains problematic, however, hindered by limited, dated statistics available on tortoise populations. To update the radiated tortoise’s status and distribution, we established a series of line transects at seven localities across its range and implemented a mark-recapture study at one of these localities (Cap Sainte Marie). Tortoises currently range from south of Tulear to east of Cap Sainte Marie, at density estimates spanning 27-5744 tortoises/km². The mark-recapture estimate for Cap Sainte Marie (1905-2105 tortoises/km²) was substantially higher than its transect estimate (654 tortoises/km²) though comparable to actual tortoise captures (1438) there. Thus, our transect density values probably err as underestimates, and from these data, we calculate a conservative total population size of 12 million radiated tortoises. We also examined mitochondrial DNA sequences (ND4 gene) for two individuals/locality in a preliminary assessment of genetic variation across the species’ range. Only two ND4 haplotypes were recovered, the more common haplotype representing 13 of the 14 individuals. We offer several conservation recommendations in light of our survey results.     

Potential gene exchange between Bacillus thuringiensis subsp. kurstaki and Bacillus spp. in soil in situ

The possible transfer of genes from Bacillus thuringiensis subsp. kurstaki (Btk) to indigenous Bacillus spp. was investigated in soil samples from stands of cork oak in Orotelli (Sardinia, Italy) collected 5 years after spraying of the stands with a commercial insecticidal preparation (FORAY 48B) of Btk. Two colonies with a morphology different from that of Btk were isolated and identified as Bacillus mycoides by morphological and physiological characteristics and by 16S rDNA analysis. Amplification by the polymerase chain reaction (PCR) of the DNA of the two isolated B. mycoides colonies with primers used for the identification of the Btk cry genes showed the presence of a fragment of 238 bp of the cry1Ab9 gene that had a similarity of 100% with the sequence of the cry1Ab9 gene present in GenBank, indicating that the isolates of B. mycoides acquired part of the sequence of this gene from Btk. No cells of Btk or B. mycoides carrying the 238-bp fragment of the cry1Ab9 gene were isolated from samples of unsprayed control soil. However, the isolates of B. mycoides were not able to express the partial Cry1Ab protein. Hybridization with probes for IS231 and the cry1Ab9 gene suggested that the inverted repeated sequence, IS231, was probably involved in the transfer of the 238-bp fragment from Btk to B. mycoides. These results indicate that transfer of genes between introduced Btk and indigenous Bacillus spp. can occur in soil under field conditions.     

The recent and rapid spread of the zebra mussel (Dreissena polymorpha) in Great Britain

This paper reviews the current, apparently rapid spread of zebra mussels (Dreissena polymorpha) in Britain, discusses the possible causes of this spread, considers the potential ecological consequences, and looks at what measures could be undertaken to minimise the impacts of zebra mussels and other invasive pests in Britain's freshwaters. Five out of 27 major water companies reported increases in their regions between 2000 and 2002 and a further three acknowledged their presence. Increases were also reported by the Environment Agency, Broads Authority, angling clubs and boatyards. No one interviewed reported a decrease in zebra mussels between 2000 and 2002. The most notable increases have been in southern, central and eastern England. A newly recorded population of zebra mussels in the River Darent, Kent, contained zebra mussels in dense mats of up to 11,000 individuals m⁻² and up to 20 cm in depth. There is evidence that the ecology of recently invaded sites has been deleteriously affected. A fishing lake in Lancashire has experienced increased water clarity and reduced fish biomass coincidental with the arrival of zebra mussels, while a newly recorded population in Barden Lake, Kent, appears to be having a deleterious impact on native unionid mussels, particularly the swan mussel (Anodonta cygnea) and, more, recently the painter's mussel (Unio pictorum). Repeated surveys in the River Thames, River Great Ouse and Barden Lake showed that the proportion of unionid mussels infested by zebra mussels had increased significantly in all sites studied during the past one to five years.