Thesis (Ph.D.)--Aberdeen University, 2008. / Title from web page (viewed on Apr. 20, 2009). Includes bibliographical references.

The population, reproductive biology and physical habitat requirements of endangered freshwater pearl mussel (<I>Margaritifera margaritifera</I> (L.)) populations in Scotland were investigated. Surveys of viable populations revealed overall densities, based on 1m² quadrat counts, of 0.27-7.98 mussels.m^-2. Total estimates for rivers, based on extrapolations of 50m transect counts, ranged from 2,000 to 0.9-3.7 million mussels. The expected predominance of young mussels was not achieved in any population. In order to test a hypothesis that juveniles were under-represented in samples, six populations first studied in 1984/85 were re-investigated in 1996/97. The relative numbers of 11-20y old individuals found in 1996/7 were consistently larger than those of 1-10y olds found a decade earlier. This provides strong evidence of sampling bias. <I>M.margaritifera</I> grow in an approximately asymptotic fashion and the von Bertalanffy equation is an appropriate descriptor. Growth may be influenced by temperature. In general, large mussels grow in large, cold rivers and vice versa; although there are exceptions, which suggest that additional factors may be involved. The timing of annual reproduction seems to be related to temperature. Mussels in the warmest rivers tend to spawn earliest. The prevalence and magnitude of natural parasitic mussel larval (glochidial) infections in wild salmon (<I>Salmo salar</I> L.) and trout (<I>S.trutta</I> L.) stocks were comparable to those reported elsewhere. Older fish seem to be less susceptible to glochidiosis than 0+ fish. Some trout stocks appear to be under-utilised by <I>M.margaritifera</I>, possibly due to differences in behaviour and/or place of origin. River bed substratum characteristics appear to be the best physical parameters for describing <I>M.margaritifera</I> habitat. Boulder-stabilised refugia, which contain enough sand/gravel for borrowing, are ideal habitats for juveniles.

The age structures of several populations have been recorded at ten year intervals for the past 20 years.  The changes in the age structures of these populations indicate that small mussels are often under recorded due to sampling bias.  Some populations show unchanged age structures indicating that levels of recruitment have been maintained, whereas others show aging population structures, with very few young mussels being recruited to the population. The habitat requirements were modelled using a number of techniques.  All the models indicate that, in Scotland, physical habitat parameters are the most important for determining habitat suitability at the between river scale.  Models of habitat requirements for juvenile mussels indicate that the sediment variables, particularly the amount of silt present, are most important, while models for adult mussels also include macrohabitat variables.  However, the resolution of these models is compromised by the effects of pearl fishing, which has reduced the densities or removed mussels from areas of otherwise suitable habitat, thus resulting in a lack of differentiation between suitable and non suitable sites. The genetic diversity and differentiation within and between populations was examined and showed that Scotland contains some populations with a high genetic diversity when compared to other populations studied in Europe.  Some populations, however, were shown to be lacking diversity, and had a small effective population size, making them vulnerable to the effects of inbreeding depression and genetic drift.  Differentiation between rivers showed that rivers geographically close were not always the most genetically similar.  This may have implications during translocation or restocking programmes. Recommendations are made for future conservation efforts.

No description available.

<p>The two papers presented in this thesis focus on population genetic study on freshwater pearl mussel populations in Sweden, using RAPD method. In paper I, I examine genetic variation within and between 5 populations in a single drainage area in south western Sweden. In paper II, I study the evolutionary relationship, and how genetic variation is related to population size, age structure and geographic isolation in 14 populations of freshwater pearl mussel in south central Sweden. In both papers I and II, I found that genetic variation was larger than found in previous studies using other techniques, and variation was larger between than within populations. I did not found any correlation between geographic and genetic distance, which indicates that mussel populations have been adapted locally to environmental factors in a relatively short time. In paper I, I found that genetic distance between populations was greater than found in other studies, despite small geographic distances. In paper II, I found that populations were highly differentiated indicating little gene flow between them. There was no significant positive relation between genetic variation and population size or age structure but there was a significant positive relation between mean age and population size indicating that many populations have gone through bottlenecks recently.</p>

The two papers presented in this thesis focus on population genetic study on freshwater pearl mussel populations in Sweden, using RAPD method. In paper I, I examine genetic variation within and between 5 populations in a single drainage area in south western Sweden. In paper II, I study the evolutionary relationship, and how genetic variation is related to population size, age structure and geographic isolation in 14 populations of freshwater pearl mussel in south central Sweden. In both papers I and II, I found that genetic variation was larger than found in previous studies using other techniques, and variation was larger between than within populations. I did not found any correlation between geographic and genetic distance, which indicates that mussel populations have been adapted locally to environmental factors in a relatively short time. In paper I, I found that genetic distance between populations was greater than found in other studies, despite small geographic distances. In paper II, I found that populations were highly differentiated indicating little gene flow between them. There was no significant positive relation between genetic variation and population size or age structure but there was a significant positive relation between mean age and population size indicating that many populations have gone through bottlenecks recently.

The general aim of this thesis was to examine the merits of ex-situ vs. in-situ strategies for the conservation of the endangered freshwater pearl mussel, Margaritifera margaritifera, and to investigate the relationship of the larval parasitic stages of the mussel (glochidia) with the salmonid hosts. To this end, I critically reviewed the literature on conservation of freshwater mussels, developed methods for quantifying the behaviour and activity patterns of adult mussels in captivity, experimentally studied host specificity, and quantified the physiological and behavioural effects of glochidia upon salmonid hosts. The results indicate that the conservation of the freshwater pearl mussel is probably best addressed at the watershed scale, and will benefit from a combination of ex-situ and in-situ techniques, as well as from a more critical assessment of findings, many of which are only reported in the grey literature. Empirical, peer-reviewed data are badly needed to inform current conservation efforts. Novel Hall-effect magnetic sensors were used to quantify and characterise discrete mussel behaviours without adversely affecting the welfare or survival of adult mussels, and these hold considerable potential for determining optimal rearing conditions for ex-situ conservation. Arctic charr was shown to be a potentially suitable host for M. margaritifera, and occupied an intermediate position in host suitability between brown trout and Atlantic salmon. Physiological impacts of glochidia upon brown trout included swelling of secondary lamellae and spleen enlargement, but the latter tended to be slight and was restricted to 1 month post-exposure. Glochidia encystment had no significant effect on blood haematocrit, respiratory performance, or cryptic colouration of brown trout hosts. The behavioural effects were more subtle and glochidiosis made brown trout more risk-averse and less willing to explore a novel habitat, without affecting the host's ability to chemically recognise and avoid cues from a predator. Overall, the results of this thesis indicate that the impacts of glochidia upon salmonid hosts are probably slight and temporally variable, and may perhaps lead to increased host survival, which would support the symbiosis-protocooperation theory of glochidia-salmonid interaction.

Mussel populations diminished from freshwaters in Europe during the 20th century, both due to human harvest and hydropower constructions. Therefore, substantial efforts have been dedicated towards restoration and reintroduction operations. Nevertheless, few studies have assessed mussel behavior in response to substrate and within stream preferences, which makes reintroduction operations uncertain and short of scientific guidelines. The aim of this study was to evaluate the importance of environmental factors for pearl mussel habitat selection and thus, provide knowledge that may make mussel introduction more successful. I investigated the behavior of freshwater pearl mussels (Margaritifera margaritifera) following introduction in a stream (Gäddbäcken) in Northern Sweden. Here, I used short behavioral trials and stream surveys to assess pearl mussel habitat preference (substrate, stream depth and water velocity) when introduced in novel environments. When comparing juvenile and adult pearl mussel behavior in my laboratory trials, I found that juvenile pearl mussels are more active (faster to do their first move) than adult mussels. In the within stream experiment, I found that there was a high correlation between water velocity and remaining pearl mussels, where mussels were more common in water with a velocity of 0.5 m/s than at lower velocities. Also, there was a positive correlation between water depth and remaining pearl mussels, where pearl mussels increased in abundance at depth over 0.3 m. My results suggesting that within stream conditions (water depth and stream velocity) can to a large part explain the pearl mussel presence at different localities in the stream. In other words, to increase the likelihood of successful introduction of pear mussels, my study indicate that individuals should be introduced to stream velocities of around 0.5 m/s and a water depth of 0.3 - 0.45 m.

<p>The number of species extinctions is increasing at an alarming rate. Long-lived freshwater mussels of the order Unionoida, which include a parasitic stage on a host fish, are highly threatened. Habitat degradation by turbidity and sedimentation is thought to be one major reason for their decline. The objective of this thesis was to examine recruitment patterns and identify the causes of the lack of recruitment in the threatened unionoid freshwater pearl mussel (Margaritifera margaritifera). In addition, I investigated the effects of turbidity on non-endangered dreissenid mussels, where turbidity was manipulated through use of bioturbating mayflies.</p><p>In a survey of 107 Swedish streams, mussel population size and trout density were both positively correlated to recruitment probability of M. margaritifera. A more in-depth study of the age-structure of nine populations revealed that four of these populations showed no signs of recruitment over the last ten years. Within-stream variation in recruitment was high as both mussels and trout had patchy distribution, and may be important for population regulation. Moreover, examination of different life stages revealed no differences in the gravid mussel stage or the stage when mussels infect salmonid fish. Instead, differences were observed for the juvenile, benthic stage, presumably related to differences in turbidity and sedimentation. High turbidity may affect filter-feeding efficiency of mussels and high sedimentation may reduce survival by clogging sediments, thereby altering, for example, oxygen and food conditions. In the study of the effects of turbidity, bioturbating mayflies increased turbidity and filter-feeding dreissenid mussels reduced turbidity. Mussel growth both decreased and increased with increasing turbidity, depending on sediment type.</p><p>Turbidity and sedimentation often impact entire stream systems, and a holistic, catchment-based management strategy may be needed to reduce the effects of sedimentation on freshwater pearl mussels. The effects of restoration take a long time and must start soon if recruitment of mussels is to be re-established. Restoration may also be more urgent in some streams than in others, as the maximum age of M. margaritifera populations in my study differed by as much as 60 years. As mussel and trout densities seem to be important for recruitment success, one conservation method may be to concentrate mussels into sites where trout density is high.</p>

<p>The freshwater pearl mussel (<em>Margaritifera margaritifera</em>) has declined dramatically throughout its range and is faced with recruitment problems in most of the streams where populations still persist. Human activities, such as forestry and agriculture, are thought to be the main reason for these problems. In this study, spatial information on landscape features along 38 streams with known recruitment status were analyzed in an effort to determine if GIS-tools could be used to identify streams with successful recruitment. Differences in the distribution of various landscape features, measured in stream corridors of 50 and 150 m, and differences in several water chemical factors between streams with and without recruitment were investigated. The distribution of landscape features was also compared with host fish (brown trout) density and any statistically significant water chemical factor.  Both mussel recruitment and trout density were found to be negatively related to clear-cuts, and mussel recruitment was also negatively related to high water color, which has been shown to be correlated with high nutrient content, one of several adverse effects of clear-cutting close to streams. Recruitment was expected to be negatively affected by roads, but no such relationship could be found. Instead, mussel recruitment was found to be positively related to the number of road crossings per kilometer, but the strength of this relationship was questionable. In addition, even though it was somewhat unclear, high proportions of lakes and ponds were found to be positive for both recruitment and high trout density. The results of the study indicate that GIS-tools can be used to find landscape features that affect recruitment of freshwater pearl mussel and they support the belief that forestry activities are an important cause for the decline of the species in Sweden. In addition, the results indicate that leaving protective zones of forest between streams and clear-cuts can be a possible conservation method for the freshwater pearl mussel.</p> / <p>Flodpärlmusslan (<em>Margaritifera margaritifera</em>) har minskat kraftigt i hela sitt utbredningsområde och i de flesta vattendrag där populationer finns kvar sker ingen rekrytering. Mänskliga aktiviteter, exempelvis skogsbruk och jordbruk, anses vara huvudorsaken för dessa problem. Syftet med den här studien var att undersöka om GIS-verktyg kan användas för att identifiera vattendrag med fungerande rekrytering. För att uppnå det analyserades geografisk information om landskapet längs 38 vattendrag med känd rekryteringsstatus. Skillnader i fördelningen av olika landskapsföreteelser, uppmätt i 50 och 150 meters buffertzoner, och skillnader i flera vattenkemiska faktorer mellan vattendrag med eller utan rekrytering undersöktes. Dessutom undersöktes även om det fanns något förhållande mellan landskapsföreteelser och tätheten av värdfisk (öring) och mellan landskapsföreteelser och signifikanta vattenkemiska faktorer. Både rekrytering av flodpärlmusslor och öringstäthet var negativt relaterad till kalhyggen. Rekrytering var också negativt relaterad till hög vattenfärg, som har visats vara korrelerat med högt näringsinnehåll, en av flera effekter kalhyggen nära vattendrag har. Rekrytering förväntades påverkas negativt av vägar, men inget negativt förhållande hittades. Istället hittades ett positivt förhållande mellan rekrytering och antalet vägkorsningar per kilometer, men styrkan av det förhållandet var ifrågasättbar. Dessutom var, om än något otydligt, andelen sjö och damm positivt för både rekrytering och hög öringtäthet. Studien indikerar att GIS-verktyg kan användas för att hitta landskapsföreteelser som påverkar rekryteringen av flodpärlmusslor och den stödjer bedömningen att skogsbruk är en av de viktigaste anledningarna till artens nedgång i Sverige. Dessutom indikerar resultaten att skyddszoner mellan kalhyggen och vattendrag kan vara en möjlig skyddsåtgärd för flodpärlmusslan.</p>