The impact of Atlantic salmon S. salar farm escapes/intentional releases of non-native salmon and stocking of fertile farm/hatchery reared individuals on the genetic integrity, fitness and long-term viability of wild populations has been the focus of considerable debate. In this study, the consequences of both a S. salar supplemental stocking programme and the long-term consequences of farm escapes are assessed. AS. salar supplemental stocking programme was established in 1996 in the River Bush, Northern Ireland, in an effort to increase the diminishing adult returns. Capitalising on this programme, in this study, 40 wild males and 40 wild females were selected as broodstock. Eggs were stripped from females and fertilized in vitro to produce 40 unique families. Resulting eggs were reared under hatchery conditions. ~90,500 un-fed fry were stocked into areas with limited spawning potential. >2,400 smolts were intercepted and genotyped for a suite of microsatellite markers and assigned to the parental broodstock. Analysis revealed that the overall percentage survival of the stocked hatchery-reared fish was 0.66%. Results are considered in terms of costs (e.g. potential genetic consequences related to mate choice) & benefits (e.g. increased production). In two classic studies, Clifford et al. (1998a, 1998b) investigated large S. salar escapes, involving adult and juvenile individuals, and their impacts on wild populations. Based on their findings the authors demonstrated that only a small proportion of adult escapes managed to successfully breed in the wild. They have also suggested that escaped juvenile farm salmon can potentially complete their life cycle, breed and interbreed with native fish upon their return to the river. In the current study, the sites of Clifford's studies were revisited 20 years later. New samples were collected and screened alongside the samples used in Clifford's studies, as well as additional samples not screened at the time. In total over 3,000 S. salar were screened for 25 microsatellites and one mitochondrial DNA marker, known to be associated with farmed fish. Results of analyses confirm limited impact of adult salmon escapes on wild populations and provide good evidence for the establishment of a farm derived population in the wild.

This thesis focuses on diversification in mastacembelid or spiny eels (Teleostei: Synbranchiformes: Mastacembelidae) from Lake Tanganyika (LT). LT is the oldest and deepest of the East African Rift Lakes, and is a world-renowned biodiversity hotspot. Chapter One introduces Mastacembelus and the concept of adaptive radiation theory. Chapter Two focuses on the origin and diversity of LT Mastacembelus, including 48% of the African non-LT species. A dated molecular phylogeny demonstrates the monophyly of the endemic Mastacembelus, which colonised LT 7-8 Ma and subsequently underwent rapid radiation forming five main lineages. Chapter Three is a comparative account of pectoral fin diversity within LT, and includes a description of a new species of endemic LT Mastacembelus lacking pectoral fins. Chapter Four incorporates two datasets to address whether LT Mastacembelus exhibit the signature of an adaptive radiation. Firstly, stable isotope analyses are used to estimate trophic niche utilisation and compare how trophic ecology is linked to phylogenetic history. Secondly, morphological diversity of LT Mastacembelus crania is assessed using 3D micro-computed tomography, and compared to the ecological data to test whether morphological traits are correlated to trophic niche exploitation and/or phylogenetic history. Chapter Five builds upon the molecular phylogeny of Chapter Two, by substantially increasing the taxonomic sampling of African species, which is now ~70% complete. This allows the endemic LT radiation to be viewed in the context of almost complete African Mastacembelidae diversity. Extended taxonomic sampling resolves a Congo species within the LT flock; this highlights the affinity of LT and the Congo Basin, and is potentially representative of an emigration and subsequent diversification of an endemic LT species in to the Congo River system. The Congo Basin taxa show high levels of diversity, and are not monophyletic. Chapter Six draws together conclusions about mastacembelid diversity and adaptive radiation, and raises areas for future research.

No description available.

No description available.

As feeding is fundamental to any animal, this thesis examined constraints on foraging behaviour from the point of view of a predatory fish, the threespine stickleback, encountering prey sequentially and simultaneously. Subsequent to prey detection, the fish orientated towards the prey and then decided to attack. The probability of attack reduced with a decrease in fish size, an increase in the size of the prey and the fish's stomach fullness and was dependent on the presence of competitors. During the attack, if the fish hung midwater the probability of successful prey capture was greater. Hanging was more likely to occur with smaller fish and when larger prey were encountered and was also longer in duration when prey were encountered simultaneously. When handling the prey, the fish made a decision to eat within the first few seconds. All of the fish ate to fill their stomachs, with the critical factors involved in prey choice being the size of the prey in relation to the size of the fish's mouth and the stomach fullness of the fish. With an empty stomach, the fish ate whatever prey was encountered. As stomach fullness Increased the fish became selective against large prey with high handling costs, depending on the availability of alternative prey. Those prey selected for had low handling costs and were successfully captured whenever encountered. Prey with a width 0.6 of the fish's jaw width were found to be the best option in terms of costs and benefits to the fish. Selectivity was, however, also a function of the capacity of the fish's stomach. The thesis demonstrates how the behavioural response of the foraging stickleback is dynamic, dependent on a number of factors external to and internal of the fish.

No description available.

No description available.

No description available.

The status of "wild" brown trout (Salmo trutta, L. 1758) populations in the UK is increasingly giving cause for concern (Giles, 1989; Crisp; 1993). Declines in freshwater stocks are often associated with anthropogenic influences destructive to river channel structure and ecosystem function which are contributing to widespread loss of salmonid habitats (Crisp, 1989; White, 2002). Chalk streams are subject to considerable habitat degradation such that rehabilitation requires management actions which better integrate habitat and ecological processes operating to influence fish populations. The influence of local meso-scale habitats upon brown trout population dynamics in two contrasting sectors of the River Piddle, Dorset, UK was quantified using the Physical Habitat Simulation Model (PHABSIM). Sectors examined represented 'typical' semi-natural chalk-stream conditions in the Piddle/Frome catchment area. Spatial availability and temporal variations in habitat quality (WUA) were modelled and tested for correlation against age-specific trout densities obtained from eight years quantitative electro-fishing data. Analyses indicated; (1) availability of marginal habitats associated with abundant bank-side cover was critical to adult over-winter survival and was a key factor determining local carrying capacity , (2) abundance of juvenile trout was strongly related to critical periods for spawning and rearing habitats, (3) low habitat durations during the first summer acted as a bottleneck at the juvenile life stage and (4) a variety of different meso-habitat types was important to juvenile recruitment dynamics. The implications of these findings are explored in the context of management of chalk rivers with respect to;- (i) habitat factors limiting trout recruitment dynamics (ii) utility of PHABSIM as a management tool for identifying population bottlenecks and (iii) potential for river rehabilitation strategies to effectively manipulate natural mechanisms regulating brown trout populations in chalk streams.

Sandeels comprise a quarter of North Sea fish biomass and are vital prey for a number of marine mammals and birds. However, in recent decades there have been significant declines in sandeel abundance and energy value. These declines have been linked to climate change, however, it is unclear what the relative influence of changes in food and temperature is. Here we examine the role of these factors on different aspects of the sandeel lifecycle and determine how robust sandeels are to expected climate warming. First, we review the evidence for climate impacts on sandeels and discuss the implications for higher trophic levels with particular reference to seabirds. Evidence summarised demonstrates that sandeels are a critical food source for many seabirds, and that declines in sandeel populations have negatively impacted seabird breeding populations. Lack of existing quantitative understanding of the influence of food and temperature on sandeels demonstrates the need for a new mathematical model to predict the outcome of climate warming on sandeel stocks. Second, we model changes in spawning and hatch dates off the Scottish east coast, which have been proposed as a contributor to the long-term decline in sandeel energy content. Results indicate that spawning and hatch dates do not explain this decline. Instead, the timing of both lifecycle events is relatively fixed and is governed by predictable environmental cues. Moreover, given the weak temperature effect on spawning and hatching, future temperature rises appear unlikely to significantly affect hatch date. The central part of this thesis is the development and use of a new dynamic energy budget model to unravel the influence of food and temperature on sandeel abundance and energy content. An important application of the model was the examination of mortality rates between 2001 and 2007, a period of pronounced stock decline off the Scottish east coast. The model was driven by food and temperature. Support was found for the hypothesis that overwinter starvation mortality contributed towards a recent decline in sandeels in northern UK waters. Highest over-winter mortality rates were recorded for juveniles and not individuals aged 1 or over due to the effect of weight-specific metabolism. However, a sensitivity analysis of the model suggests that mortality rates are more sensitive to changes in copepod abundance in the build up to overwintering rather than temperature during overwintering. We suggest that food-driven size-selective starvation mortality may have contributed to the stock decline off the Scottish east coast. We therefore conclude that indirect food web effects of climate change are likely to be greater than direct physiological effects on sandeels.