The effects of metal contamination on larval white sturgeon in the upper Columbia River

Sturgeon populations are imperiled worldwide. Declines are attributed to many factors including habitat degradation and alteration, overexploitation, and contamination. In North America, white sturgeon (Acipenser transmontanus) populations in the upper Columbia River (UCR) face many of the same factors. White sturgeon in this system have been declining for decades due to a lack of recruitment to the population, despite evidence of spawning and early larval survival in the wild. Early life stage white sturgeon are among the most sensitive of aquatic species to copper. The UCR has been contaminated with metal laden slag and liquid effluents from smelter and mining activities, resulting in UCR sediment metal concentrations, including copper, being elevated. The goal of my dissertation was to understand the potential role of metal contamination in the decline of white sturgeon in the UCR. This effort included toxicity tests with copper contaminated water as well as sediments collected from the URC, with a focus on the behavioral responses of exposed fish as a consequence of sublethal exposures. In chapter 1, I exposed early life stage white sturgeon to sublethal concentrations of copper, one of the contaminants of concern in the UCR, to characterize and quantify the effects of copper on swimming and feeding behavior. I found that changes in larval sturgeon swimming behavior were apparent up to seven days earlier than mortality and that copper exposure reduced food consumption in juvenile sturgeon. Critical swimming performance, however, was not affected by copper exposure. While not directly lethal, these alterations in behavior would impair a sturgeon's ability to locate, capture, and consume prey, thus impacting survival. In chapter 2, I evaluated the toxicity of metal contaminated sediments from the UCR to larval white sturgeon. Sediment was collected from six sites in the transboundary reach of the UCR. All six sites had elevated metal concentrations above equilibrium partitioning sediment benchmarks, which would suggest the metals could pose a risk to benthic invertebrates. The overlying water metal concentrations were also above water quality criteria levels in three of the six sites. I found sediment at one site reduced survival and affected swimming behavior of larval sturgeon.In chapter 3, I provide a synthesis evaluation of white sturgeon life history with what has been reported about metal contamination in the UCR, including documented concentrations from the river, and what we know about how metals affect larval sturgeon behavior and survival. Of particular concern are reported field observations of large numbers of sturgeon larvae with empty guts at a critical point in their life cycle. By putting all these pieces together, I found that metal contamination in the UCR could be reducing the prey base of larval sturgeon, altering swimming behavior to increase likelihood of starvation or predation, and evidence of an additional exposure route when larval sturgeon ingest sediment. Thus, the most important findings from my dissertation include 1) low, environmentally relevant concentrations of copper alter swimming behavior of larval sturgeon indicative of sublethal injury, 2) sediments collected from the UCR can affect larval sturgeon survival and swimming behavior, and 3) metal concentrations measured at some sites in the UCR are above effect concentrations from laboratory studies. These findings suggest that metal contamination could be a factor in the decline of the upper Columbia River white sturgeon, and should be considered in recovery efforts for the population

Early Life History Dynamics Of Lake Sturgeon

Thesis (Ph.D.) University of Alaska Fairbanks, 2009Populations of lake sturgeon Acipenser fulvescens in the Laurentian Great Lakes have not recovered after dramatic declines in the late 1800s despite the implementation of numerous recovery plans. Although extensive lake sturgeon research has and continues to occur, critical knowledge gaps remain. Recruitment of lake sturgeon is variable, but the extent of that variation, its limiting factors, and mortality rates experienced by early life stages are unclear. The purpose of this study was to increase our understanding of lake sturgeon early life stages by examining characteristics of a remnant population in the Peshtigo River, Wisconsin. Specifically, this research sought to empirically estimate rates of early life stage mortality, describe the vertical distribution of drifting larvae, evaluate the impacts of predation on recruitment, and describe patterns in movement and abundance of age-0 juveniles. Extensive sampling of lake sturgeon eggs, larvae, age-0 juveniles, and potential predators occurred during 2006 and 2007. Although drifting lake sturgeon larvae were captured in all parts of the water column, more were found near the surface than the substrate. After drifting to nursery areas, individuals exhibited variable movement patterns. Some fish were never recaptured more than 10 m from the initial capture site, while other individuals moved more than 9 km. Even though absolute abundance of juveniles differed by an order of magnitude between 2006 and 2007, a pattern of steady decline during the summer months was similar during both years. This downstream movement may have resulted in emigration from the Peshtigo River, as there was no evidence of predation on this life stage. Overall mortality from the egg to age-0 juvenile life stage exceeded 99.9% in both study years. Predation on eggs was extensive by both crayfish and fish (white sucker Catostomus commersonii ), but was minimal on other life stages. These results suggest that recruitment can vary significantly, and predation is likely only limiting at the egg life stage. These results will allow more effective monitoring and management of lake sturgeon early life stages, thereby promoting population recovery

Etude expérimentale des effets des conditions environnementales (température, oxygène, polluants) sur la survie, le développement et le comportement des stades embryo-larvaires d'esturgeon européen, Acipenser sturio

The European sturgeon Acipenser sturio is a diadromous species which has exibited a drastic decline during the 20th century. Its last population lives in the Gironde-Garonne-Dordogne (GGD) catchment where the last documented reproduction occured in 1994. Individuals released in the context of restocking actions are expected to re-enter the system for reproduction in the next few years. Because of global changes and human activity evolution, environmental conditions have changed from the last reproduction. Improved knowledge on the sensitivity of the European sturgeon to temperature, dissolved oxygen and pollutant is required to evaluate its capacities to recolonize the GGD catchment. Sentivity to present and future, considering global changes, oxygen and temperature conditions were evaluated as well as quality of the substratum of potential spawning grounds. The sensitivity of the early stages toward a mix of pollutants found in the GGD catchment was evaluated. Results obtained show a high sensitivity of the young stages of this species to oxygen concentration. Thermal optimum, optimal and critical tolerance windows were determined. Sensitivity to pollutants mixtures found in the GGD was relatively low. Dordogne river substratum was globally more toxic than Garonne river substratum. Beauregard and Pessac-sur-Dordogne were tested respectively as the best and the worst potential spawning ground for the development of the European sturgeon early stages according to their toxicological effects. Current conditions in the GGD catchment seems to be sustainable for European sturgeon early stages. Data from this study would be useful for further restocking programs in the historical european sturgeon reproduction area.L'esturgeon européen Acipenser sturio est un poisson migrateur amphihalin qui a connu un fort déclin au cours du 20ème siècle. La dernière population vit dans le bassin Gironde-Garonne-Dordogne (GGD) et sa dernière reproduction connue date de 1994. Les individus relachés lors de repeuplements sont supposés venir se reproduire prochainement. Du fait du changement global et de l'évolution des activités humaines, une meilleure connaissance de la vulnérabilité des jeunes stades de A. sturio vis-à-vis de la température, de la disponibilité en oxygène et des polluants s'est avérée nécessaire. La sensibilité aux conditions oxythermiques actuelles et à venir a été évaluée ainsi que la qualité des sédiments des frayères. Enfin, la sensibilité des jeunes stades de cette espèce à des mélanges de polluants représentatifs du bassin GGD a été également évaluée. Une forte sensibilité des jeunes stades de A. sturio au taux d'oxygène a été mise en évidence. Les fenêtres optimales et critiques de tolérance ont été estimées. La toxicité des sédiments de frayères de Dordogne est globalement supérieur à celle des sédiments de frayères de Garonne. Beauregard et Pessac-sur-Dordogne semblent être respectivement les sites les plus favorables et défavorables aux jeunes stades. La sensibilité de A. sturio aux polluants rencontrés dans le bassin est relativement faible. Les conditions environnementales actuelles du bassin GGD semblent globalement satisfaisantes pour accueillir le développement de jeunes stades de A. sturio. Les données collectées dans cette étude pourront servir pour d'autres programmes de réintroduction de cette espèce

Life History Analysis of James River Atlantic Sturgeon (Acipenser oxyrinchus oxyrinchus) with Implications for Management and Recovery of the Species

Sturgeon species (family Acipenseridae) are threatened globally due to habitat destruction, pollution, and overfishing. The Atlantic sturgeon Acipenser oxyrinchus oxyrinchus was listed as a federally endangered species in 2012. Atlantic sturgeon have a complex life history that utilizes a wide range of habitats. Timing of life history varies in different areas requiring each population to be studied. Very little work has been published on Atlantic sturgeon reproduction in the James River, Virginia. To aid the recovery of James River Atlantic sturgeon, aspects of life history need to be addressed. To increase understanding of Atlantic sturgeon life history a length at age model was created to show population structure and age of sexual maturity. Telemetry experiments were conducted to determine what types of boats are likely to cause boat strike mortalities of adult fish during a spawning season. Morphometrics, sperm characteristics, and telemetry data were used to determine if Atlantic sturgeon have a fall spawning season. Strontium/calcium ratio analysis was conducted on Atlantic sturgeon fin spines to better understand migration patterns. Cortisol levels were examined in Atlantic sturgeon exposed to MS222, electronarcosis or no anesthetic 1 and 24 hr after a small incision mimicking tag implantation. I also determined the feasibility of using electronarcosis in the field and the effect of salinity on electronarcosis. The length at age data show male Atlantic sturgeon beco,e sexually mature at age 10 y and females around age 15 y. Telemetry data showed that deep draft ocean-cargo ships are most likely responsible for boat strike mortalities and there is a greater chance of Atlantic sturgeon being hit in the narrow portion of the river. Electronarcosis is an effective anesthetic and has various attributes that make it better suited for field applications then frequently used chemical anesthetics. The data generated from this research will help management produce effective recovery plans and create a safer research environment for both the fish and researcher

Optimisation of common snook Centropomus undecimalis broodstock management

Advances in aquaculture technologies are being investigated to support the replenishment of local fisheries, develop marine food fish farming opportunities and to increase seafood production globally. In order to promote the expansion and development of aquaculture technologies required to raise new finfish species, a number of key bottlenecks restricting commercial-scale culture need to be addressed, including the ability to control fish reproduction in captivity and to produce high quality seeds. One candidate species for large-scale production, and the focus of this work, is common snook. Prized as a food fish in Mexico, Central and South America and as a popular game fish along the Gulf coast of the United States; common snook are economically important having both a high market value and recreational demand. Despite recent advances in captive spawning, a number of reproductive bottlenecks still need to be addressed such as lack of spontaneous spawning in captivity, poor fertilization rates and inconsistent production of high quality eggs and larvae. Therefore, the overall aim of this thesis was to better understand the reproductive biology of common snook in order to develop protocols to improve the reliability of captive spawning in closed recirculating aquaculture systems and the quality of eggs produced as a basis for commercial scale cultivation. First, this PhD project described oocyte development in common snook and validated a non-invasive method for assessing reproductive condition in wild and captive stocks (Chapter 2). This was done by using a tiered and adaptable staging scheme to compare the wet mount technique with histological preparations of ovarian biopsies. When compared with histology, the wet mount provided an immediate and precise method for determining whether female broodstock were candidates for hormonal induction. In fishery biology, an understanding of fish reproductive success and population reproductive potential is critical for designing and implementing effective fisheries management strategies. The wet mount technique provides a tool for non-lethal, low-cost determination of reproductive status in wild fish stocks. The next research chapter focused on spawning induction of captive snook populations. The first trial compared the effects of slow and regular release GnRHa implants whereas the second trial investigated the effects of GnRHa, alone or in combination with the dopamine antagonist, pimozide (PIM), on milt characteristics and plasma steroid levels in captive male common snook broodstock (Chapter 3). In an effort to better enable reliable control of reproduction under captive conditions, the annual plasma sex steroid profile of captive male and female broodstock maintained under natural photo-thermal conditions was also examined. When possible, milt samples were collected pre and post implantation; sperm density, sperm motility and spermatocrit were documented among individual males. The assigned treatments appeared to have no or little effects on milt production in male broodstock although plasma steroid levels were found to be significantly elevated in individuals treated with GnRHa in combination with the dopamine antagonist, pimozide. At the time this work was performed, no data on spawning dynamics, including individual spawning performance, had been reported for common snook in captivity. Mass spawning tanks are complex systems where fish are left to spawn naturally and fertilized eggs are collected with little or no control over the mating of the animals. Therefore, the third part of this thesis explored the potential of DNA profiling for monitoring mating outcomes in captive broodstock by employing eight microsatellite markers to detect and quantify individual parental contributions for 2,154 larvae obtained from the three broodstock tanks (Chapter 4). The panel of loci was generally robust and allowed unambiguous assignment of 89% of larvae to a single family. Overall, spawn contribution data 1) provided a confirmation of GnRHa treatment efficacy in female snook with a minimum stage of oogenesis (late secondary growth-SGl) required for successful spawning, 2) identified a potential impact of handling on maturation and spawning of captive broodstock and 3) confirmed that, through photothermal conditioning, captive broodstock can spawn over consecutive days and several times per year including outside of their natural spawning season. The exogenous cues that tropical species use to synchronize key life events like reproduction remain largely unstudied, therefore, my PhD project also investigated the influence of tidal cycle on reproductive activity in common snook (Chapter 5). Real-time quantitative RT-PCR assays were developed and validated to measure the temporal expression patterns of gonadotropin genes (fshβ and lhβ) during the reproductive cycle in males and females. These were evaluated in relation to sex steroid production, LH blood plasma levels, gonadal development and tidal cycle. The phylogenetic analysis of the deduced amino acid sequence of common snook for fshβ and lhβ revealed strong identity with other teleosts (75-90%). Additionally, the mRNA profiles of fshβ and lhβ in the pituitary of females displayed a clear pattern of expression concomitant with histological changes in oocyte development. Histological observations of gonads suggested a circa-tidal rhythm of follicular development. The findings, as a whole, provided new information supporting the role of tidal cycle on the entrainment of gametogenesis allowing for a better understanding of the environmental control of reproduction in common snook. Although the primary research emphasis in this PhD was on broodstock spawning and gamete quality, the final chapter focuses on larval ontogeny. The goal of this research was to gain improve understanding of the early life history characteristics of common snook in order to improve larval culture technologies. To do so, a combination of digital photography and histological techniques were used to document the embryonic and early larval development (0 to 14 days post hatch-DPH) of hatchery-reared individuals (Chapter 6). Larvae hatched 15 h after fertilization at 28°C, lacked pigmentation, had a rudimentary digestive tract and undeveloped visual system. Development was rapid and by 3 DPH larvae had almost doubled in length, the yolk sac was nearly exhausted, the mouth was open and eyes were pigmented with a well-structured retinal layer. The alimentary canal was differentiated into three distinct sections including the foregut, midgut and hindgut. Food was observed in the gut (rotifers) and structural epithelium organelles, such as the nucleus, mitochondria, and dark vesicles, were all present in high numbers. The swim bladder was formed and inflated. In summary, understanding early ontogenetic development in common snook can help provide information needed to address key bottlenecks seen in captive cultivation, such as the high incidence of larval mortality observed during the transition from endogenous to exogenous feeding. Overall, this doctoral work 1) validated molecular and endocrine analytical tools for future studies of common snook reproductive physiology, 2) provided a better understanding of both broodfish requirements in tank systems as well as the endocrine control of reproduction and spawning at the level of the brain-pituitary-gonadal axis, 3) increased our knowledge in genetic management of captive broodstock, in terms of parentage assignment and 4) offered new insight into wild population reproductive strategy as well as how reproduction is entrained through environmental cues and the pathways leading to oocyte recruitment and maturation. The new information presented here can be used to conserve wild snook stocks through production of farm raised individuals as a sustainable source of seafood and for fisheries enhancement

Mitigating the impacts of river flow regulation and barriers to fish spawning migrations

Globally, migratory fish are threatened by anthropogenic modification to rivers. These create barriers that prevent fish accessing spawning grounds required for completion of life cycles. In order to make informed decsions, for mitigating the associated negative impacts, an understanding migratory behaviour when reaching barriers during the spawning migration is required. That said, there is a lack of information about the response of migratory fish to operational regimes in regulated rivers and the areas occupied, delays caused and routes taken around infrastructures. This study investigated the behaviour of three migratory fish species under operational regimes of three different infrastructures during each species’ respective spawning season. The efficiency of a bypass channel that utilised the relationship between migratory behaviour and flow was also investigated for a further species.The literature was reviewed to identify the different types of migratory life histories of fish, the impact of different riverine modification on the respective spawning migrations and how this can be mitigated. Fish have evolved in direct response to the natural flow regime and connectivity of riverine habitats, but barriers to migration exist from source to sea. This regulates or disrupts the flow regime and connectivity that fish depend upon, which has had considerable detriment to many migratory fish species globally. The main conclusion of the review was that knowledge gaps exist for the target species, and understanding the behaviour of the study species during the spawning migration is essential to improve access to spawning grounds in regulated rivers and ultimately conserve populations.The effects of timing, magnitude and duration of eleven artificial flow (freshet) releases from two impounding reservoirs on river-resident brown trout (Salmo trutta L.), a species known to undertake spawning migrations, was investigated using radio telemetry in a regulated upland river in northern England. Most did not perform movements characteristic of spawning migrations; all were located within 10 m of the location occupied before freshets, and fish in a control reach behaved comparably. The largest unidirectional movements mostly occurred during elevated river level due to rainfall and reservoir overtopping events; other varied length movements occurred during natural peaks or low flow, indicating artificial freshets were not directly responsible, and may not be suitable to stimulate migration in river-resident fish in regulated rivers.An acoustic telemetry study was conducted to determine the impact of a high- head hydropower station, associated diversion weir and spillway on downstream migrating shortfin eel (Anguilla australis) in the regulated Wairua catchment, Northland, New Zealand. Despite the diversion weir providing an alternative route, 88% (n = 21) of tagged eels that were detected here entered the power station forebay; of these, 52% were impinged onto intake screens, always when turbines were operating at greater than 3.04 MW/day. The rest (48%) passed the spillway and continued their migration, sometimes after long delays and having spent time immediately upstream of the intake where fitness could have been reduced due to high flows. Based on findings, the most effective mitigation here and at similar power schemes is considered to be operational or physical changes at the diversion weir to minimise entry of downstream migrating eels into the power canal during the migration period. Also discussed as potential solutions are turbine shutdowns, ensuring the spillway is available and provision of a bypass channel in the forebay.At a pumping station in the Anglian region, UK, where the upstream river level is maintained primarily by a co-located gravity sluice door, route choice and behaviour of downstream migrating European eel (Anguilla anguilla) (n = 7) immediately upstream of both routes was investigated using acoustic telemetry. During the study, three eels passed through pumps despite only operating for 8% of the time the gravity sluice was open, and only two passed through the gravity sluice after arriving when it was closed; the remaining two retreated upstream. No eels were detected within 15 m of the gravity sluice when it was open and eel behaviour was indicative of reluctance to pass through pumps. Findings are discussed in terms of water resource management to implement operational changes, to make the gravity sluice an attractive downstream passage route for migrating eels and thus reduce passage through hazardous pumps.The efficacy of two bypasses in attracting and passing downstream migrating American eels (Anguilla rostrata), designed to utilise the relationship between eel migratory behaviour and flow through two methods of flow creation, i.e. an airlift and a siphon, was tested in a simulated forebay environment, as a potential remediation measure at infrastructures requiring eel passage. Under entrance velocity of 1.2 m/s in eight test runs, both bypasses performed comparably and eels tested in each readily located, entered and passed. Test findings are discussed in relation to real-world application at sites with different characteristics, and the suitability of each design in successfully providing a safe route for downstream migrating eels

Pharmaceuticals in the environment : occurrence and exposure effects in non-target fish species

A contaminação por fármacos nas zonas costeiras constitui um problema ambiental emergente, onde os fármacos neuroativos são de particular importância porque bioacumulam em espécies não-alvo, afetando o sistema nervoso central e causando efeitos ao nível das populações. Os resultados demonstram, na literatura existente, os diversos efeitos adversos da exposição de fármacos neuroativos em peixes, apesar de incidir sobre poucos compostos e maioritariamente espécies de água-doce. A bioconcentração é também insuficientemente considerada e raramente estudada em combinação com outras respostas biológicas, dificultando a conjugação entre concentração interna e efeitos observados. A estimativa da bioconcentração dos fármacos neuroativos através da sua lipofilicidade não é direta e depende de múltiplos fatores experimentais, o que dificulta a previsão de risco. Contudo, concentrações ambientais de nove fármacos neuroativos excedem ou estão próximas de concentrações que causam efeitos deletérios em peixes. Dados ambientais, com a deteção de até 28 fármacos neuroativos em águas superficiais e peixes, evidenciam a ubiquidade e diversidade destes compostos em estuários, sendo que o padrão de bioacumulação em sete espécies de peixes foi independente da lipofilicidade dos compostos, do uso do habitat ou do nível-trófico das espécies, com maior frequência e concentrações observadas no cérebro, seguido do fígado e músculo. Experiências de curta e longa exposição a fármacos neuroativos com duas espécies estuarinas/marinhas demonstraram a toxicidade de fármacos com diferentes modos-de-ação, revelando maior acumulação e toxicidade do fármaco neuroativo, fluoxetina, em comparação com outros fármacos frequentemente detetados. As respostas sub-individuais revelaram efeitos em processos essenciais (e.g. mecanismos antioxidantes, biotransformação, metabolismo energético), enquanto efeitos individuais de relevância ecológica (e.g. crescimento, comportamentos alimentares e locomotores) ocorreram após exposição crónica, ou aguda a concentrações mais elevadas. Em suma, novos conhecimentos relativos à presença, acumulação e efeitos da exposição em peixes, demonstram a necessidade de priorizar a investigação e monitorização dos fármacos neuroativos em ecossistemas costeiros.Pharmaceutical contamination in coastal ecosystems is an emerging environmental issue, with neuroactive pharmaceuticals of particular concern as they bioaccumulate in non-target fish, affect the central nervous system and can trigger population-level effects. The presented outcomes disclose recent research efforts, revealing multiple adverse effects of exposure to neuroactive pharmaceuticals in fish, albeit skewed data concerning few neuroactive compounds and largely freshwater species exist. Moreover, bioconcentration is seldom considered and rarely determined in combination with other endpoints, hampering the link between internal dosage and effects. Also, estimating the bioconcentration of neuroactive pharmaceuticals through lipophilicity is not straightforward, depending on multiple experimental factors. Here, nine neuroactive compounds were signalled as potentially threatening in aquatic ecosystems due to environmental concentrations either exceeding or near thresholds known to significantly affect fish behaviour, growth and condition or reproduction. Up to 28 neuroactive pharmaceuticals were detected in estuarine surface waters and seven fish species demonstrating the diversity and pervasiveness of neuroactive compounds in both high and slightly impacted coastal ecosystems. Bioaccumulation among all species revealed no clear pattern linked to compounds lipophilicity, species habitat use or trophic level, with higher frequency and concentrations observed in the brain, followed by liver and muscle tissues. Acute and chronic exposure experiments with two estuarine/marine fish species evidenced the toxicity of three pharmaceuticals with different modes-of-action, highlighting higher uptake and toxicity of the neuroactive com-pound fluoxetine in comparison to other frequently detected compounds tested. Sub-individual measurements revealed effects on critical processes (e.g. antioxidant and biotransformation mechanisms, or energetic metabolism), whereas individual-level effects of higher ecological relevance (e.g. alterations to growth, feeding or activity behaviours) followed chronic exposure or acute exposure at higher concentrations. Overall, critical insights on environmental fate and exposure effects in fish are provided, highlighting the need for priority research and continuous monitoring of neuroactive pharmaceuticals in coastal ecosystems

Biological invasions in brackish waters

Invasive non-native species (NNS) cause deleterious ecological, economic, social impacts worldwide. Brackish waters are transitional areas subject to invasion by taxa that may subsequently spread into adjacent freshwater and marine systems. The tendency for ports to be situated in brackish estuaries makes them particularly susceptible to ship-borne introductions of NNS. Despite being reported as heavily invaded ecosystems with a disproportionately high abundance of NNS, studies on biological invasion in brackish waters has received considerably less attention than truly freshwater and marine systems. In this thesis, I investigate the discovery, ecological impacts, and management of NNS in brackish waters. I begin by conducting a systematic review and meta-analysis comparing the ecological impacts of NNS in brackish, freshwater, and marine environments around the globe. I reveal that NNS have led to an overall decrease in the abundance and diversity of the resident communities in freshwater and marine environments, but not in brackish waters. NNS in brackish estuaries provide novel habitats, which can facilitate the establishment of other NNS, leading to an invasional meltdown. Next, I explore the first records of all freshwater, brackish and marine NNS in Great Britain and show that many NNS were first discovered in estuaries and often aggregated around the major shipping ports. This result provides support that many marine and freshwater NNS in Great Britain could have been introduced via international ships visiting brackish waters. I then focus on one NNS, the Gulf wedge clam, Rangia cuneata, which is a brackish water bivalve currently invading European waterways. I show that the growth and feeding rates of R. cuneata differed at the two extremes of salinity tolerated by this species, and consider how this intraspecific variation might drive context-specific ecological impacts. I go on to demonstrate the potential detrimental impacts of R. cuneata as a result of their much higher feeding rates and greater functional responses compared to a sympatric, native unionid mussels. I finish by investigating two methods to control invasive species in brackish waters. I show that using saline, but not freshwater, shock could effectively control R. cuneata. I then demonstrate the effectiveness of two new formulations of microencapsulated biocides in controlling R. cuneata. Taken together, these studies provide important insights into the discovery, impacts and management of NNS in brackish waters. My findings demonstrate the need for greater monitoring for NNS in brackish systems, and especially those subject to high ship traffic. The control methods proposed here have wide application in many brackish systems and for many species, thus providing much needed effective tools for the rapid response to the discovery of high risk invasive NNS in this important but overlooked transitional habitat.This study is funded by a Gulbenkian Yuval Cambridge Studentship at Churchill College and a Graduate Scholarship from Natural Sciences and Engineering Research Council of Canada