The fate of farmed fish after escape is poorly understood. The extent to which these fish might impact freshwater ecosystems is dependent upon their survival and distribution in the wild. I simulated small- and large-scale escape events from two commercial aquaculture operations in Lake Huron over 2 years. I combined the use of telemetry (120) and Floy (1000) tags to determine the fate of escaped farmed rainbow trout (Oncorhynchus mykiss). Once released, escapees dispersed rapidly, showed low site fidelity (~15% after 3 months) and were capable of long distance movements (up to 360 km). Rainbow trout experienced low survival (~50%) but maintained high growth rates both at and away from the farms. The results of this study provide a strong basis for understanding the potential risks that farmed fish may pose to the Lake Huron fish community and ecosystem in an escape event.

This thesis investigates the comparative growth and mortality of a naturalized (wild) and domestic (aquaculture) strain of rainbow trout (Oncorhynchus mykiss) common to Lake Huron. I first conducted a laboratory-based experiment, comparing the growth rates of the two strains. Under optimal and competition treatments, the domestic strain achieved a body weight ~2x that of wild conspecifics. Next, I conducted a replicated, whole-ecosystem study comparing the same strains. Both strains experienced equally low survival and the domestic strain segregated into a fast-growing group, (~3x growth relative to the wild strain), and a slow-growing group that had a lower growth rate than wild trout. A high growth rate for fast-growing domestic trout was achieved by a reliance on high energy prey as well as through low metabolic costs relative to wild strains. Together, these results demonstrate that aquaculture strains of rainbow trout have greater growth potential relative to wild conspecifics and may outcompete them in nature.

Open net-pen aquaculture allows for free exchange of materials between farm and wild environments. Increased habitat complexity in the form of farm infrastructure produces effects similar to fish aggregating devices and artificial reefs, altering the distribution and abundance of fish species within the greater area. The continuous input of nutrients via fish waste and uneaten food pellets can amplify such effects, leading to large and persistent aggregations of wild fish near aquaculture sites. These aggregations have been quantified in numerous geographical locations but data are lacking for salmon farms in coastal British Columbia. The footprint of the attractive effects is also poorly understood in all cases as research has focused on fish populations directly associated with the infrastructure. In this study wild fish populations were quantified at shallow rocky ecosystems adjacent to salmon farms in the Broughton Archipelago and compared to paired reference sites with similar habitat characteristics to test for aggregating effects. Two SCUBA divers performed visual surveys along six 25x4x4m transects at each site, three at each of two depth ranges: deep (12-16m) and shallow (6-10m). Species, abundance, and estimated total length, as well as temperature, salinity, rugosity, and visibility were examined. A combination of multivariate and univariate statistical analysis were performed to compare the physical characteristics, community composition, number of individuals, and biomass between farms and reference sites. The overall community composition was significantly different at farm sites despite no difference found in the physical habitat characteristics between treatments. This difference was predominantly driven by five fish species, yellowtail rockfish (Sebastes flavidus), copper rockfish (Sebastes caurinus) quillback rockfish (Sebastes maliger), shiner perch (Cymatogaster aggregata) and striped perch (Embiotoca lateralis). Presence/absence data showed no significant difference in species identity between farms and references, implying that the difference in community composition was primarily driven by changes in abundance rather than species identity. The total number of fish and biomass of all fish species was also significantly higher at farms. These results suggest that salmon farms in the Broughton Archipelago alter the community structure and increase the abundance of near-field wild fish populations. The aggregating effects are asymmetric within the community, with higher trophic level species showing the greatest increases in abundance. The potential implications of these results include a greater risk of disease and parasite transfer between farm and wild fish, as well as within each population. The ecological relationships among species may also be compromised with predator amplified communities potentially exhibiting top-down effects on the rest of the food web. Changes to wild fish communities seen up to 170m away from farm infrastructure suggest that the mechanism of the attractive effects may be driven more by nutrient subsidies than the presence of infrastructure. This work underscores the need to determine the full spatial extent and mechanisms of attractive effects as well as the ecological implications of persistent aggregations of wild fish near salmon farms. / Graduate

Biofouling in salmon aquaculture is an important issue. The use of copper based antifoulants contributes to marine pollution and managing biofouling on untreated nets incurs a heavy cost on the industry. What is needed is an antifoulant coating that balances the needs of the industry with good environmental practices. This study describes the effectiveness of seven alternative netting treatments and two copper based treatments as compared to an untreated nylon net. Effectiveness was measured in terms of percent net occlusion, percent cover of major fouling groups and biomass. Following eight months immersion, results show that the alternative treatments did not out-perform the untreated nylon control, and that the two copper treatments significantly outperformed the control and all of the alternative treatments tested in this study. The results demonstrate that the alternative treatments tested in this study were unable to meet the performance standards set by industry, that more research is needed into alternative antifoulant coatings for aquaculture, and that the effectiveness of copper based treatments will continue to be a barrier to the implementation of alternative antifouling treatments. / Graduate

<p>Aquatic food webs are comprised of complex spatial and temporal interactions within and among trophic levels. Human manipulations, such as construction of reservoirs, enhance uncertainties in our understanding of aquatic food web structure. Reservoirs are novel ecosystems which contain a unique composition of species. Species introductions into reservoirs may disrupt interactions within an already complex and poorly understood food web. In Scofield Reservoir in central Utah, a rapidly expanding population of Utah chub poses a detrimental threat to the blue-ribbon trout fishery. The Utah Division of Wildlife Resources has recently stocked cutthroat trout and tiger trout (a brown trout x brook trout hybrid) to potentially reduce Utah chub numbers as well as to enhance the sport fishery. I used standard fisheries techniques to describe food web interactions and to assess the potential for these piscivorous trout to control the expanding Utah chub population, as well as to determine sport fish performance and quantify diet overlap amongst top predators. Using bioenergetic modeling, I estimated very high rates of Utah chub consumption by cutthroat trout and tiger trout. These two species collectively display control of Utah chub, as the chub population is no longer exponentially increasing. Cutthroat trout and tiger trout are likely not food limited and convincingly exhibit high performance, as abundance of Utah chub is still extremely high. Both diet and stable isotope analysis showed significant overlap between these top piscivores in the reservoir, but also substantial overlap between cutthroat trout and rainbow trout with respect to Utah chub. Analysis of rainbow trout suggested this species is performing poorly; rainbow trout had extremely low catch rates and never switched to a piscivorous diet at larger sizes. Utah chub and rainbow trout had similar diet compositions, and thus rainbow trout may be competing (poorly) for food and space resources. This study contributes to our understanding of interspecific interactions among these unique assemblages of top predators in this artificial system. This research also provides knowledge to fisheries managers tasked with providing optimal sport fisheries in these artificial and dynamic systems, as well as expanding on our extremely limited knowledge of tiger trout ecology.

Most of the scientific knowledge on the pelagic fish (the clupeids Stolothrissa tanganicae and Limnothrissa miodon and the centropomid Lates stappersii) of Lake Tanganyika is from research carried out in localised areas. This makes it difficult to extend the results to the whole lake. Consequently, there is the need to study the pelagic fish resources on a lake-wide basis using the same data collection procedures. Within the framework of an international fishery research project, data from the commercial fisheries targeting the pelagic fish stocks were simultaneously collected at various sampling sites in the riparian countries. Fishery-independent data were also obtained from lake-wide research surveys. The life histories of the three fish species appear to be similar throughout the lake. However, fish distribution across the lake is very uneven. The clupeid S. tanganicae mostly occur in the northern half of the lake and is much reduced in southern areas. This appears to be a recent contraction of the distribution range of this species. Limnothrissa miodon is more evenly distributed than S. tanganicae. The two species have a different inshore-offshore, size-related distribution across the lake. Nursery grounds of the first are close to the shore while those of S. tanganicae are in open, pelagic waters. With increase in size, S. tanganicae tend to move inshore while large L. miodon display the opposite movement. Lates stappersii stock, although relatively common, tends to be at higher concentration in the deep, steep central and southern basins. The feeding ecology of L. stappersii varies depending on the area and prey availability, but is mainly based on S. tanganicae and pelagic shrimps. Local occurrence of S. tanganicae is associated with that of copepod prey. The fish stocks experience different exploitation rates across the lake. While the fishing pressure is not excessive in the most of the lake areas, in others local overfishing is taking place. The biological characteristics of the pelagic fish species are discussed for the management of the lake fisheries. Fisheries management options are formulated on the basis of the assessment of the current exploitation levels.

Philippine aquaculture is a dynamic industry and a fast growing sector of the economy. Tremendous progress in production and technology has been achieved during the past decade. However, the country is experiencing a fish production shortfall which the aquaculture sector is expected to address. Given the proper support and direction, the aquaculture industry in the Philippines has great potential for growth and development. The Philippines has the principal attributes necessary for expansion of aquaculture production (e. g. important aquaculture species, ideal climatic conditions, existing fish farms and large water resources, expertise and manpower, markets, technologies). As part of the present research, several production-oriented studies were conducted for the development of the brackishwater aquaculture sector. The studies have shown that aquaculture technologies are available (e. g. milkfish - semi-intensive culture in ponds and marine cage culture, salt-tolerant tilapia hybrid - pond-based and marine-based cage culture, grouper - pond culture, shrimp - semiintensive culture) which are technically feasible and financially viable under present economic and environmental conditions. However, there are several important aquaculture constraints (e. g. seed supply and quality, feed supply and quality, government policies, marketing and post-harvest, environmental degradation and diseases, aquaculture credits) that must be overcome in order for the country to attain the maximum benefit from the potential of aquaculture. The study also identifies the important socio-economic benefits that can be derived (e. g. contribution to Gross Domestic Product, fish food supply, foreign exchange earnings, employment opportunities, tax revenues) from the development of the aquaculture sector. Finally, the study provides some strategies for the development of the brackishwater aquaculture sector with emphasis on the culture of milkfish, salt-tolerant tilapia hybrid, grouper and shrimp.

The biological characteristics of the adult sea trout stock in the River Tywi were examined between 1988 and 1992 by sampling catches from a temporary main-river trap, and the commercial seine, commercial coracle and recreational rod fisheries. Radio tracking of adults during the spawning season investigated behavioural activities and their possible effects on stock characteristics. Catch effort data from angler log books assessed the annual performance of the rod fishery between 1990 and 1993. The effects of ameliorating the impact of acidification on water quality, benthic macro-invertebrates and juvenile salmonids, through reservoir liming, was studied.

The crabs Cancer pagurus (L) and Necora puber (L) are exported live, in bulk, from the UK to various continental countries. The success of this relatively new trade is marred by the incidence of mortalities and impaired quality of the delivered product. These studies addressed various causes - procedural and biological - of these events.Descriptions are given of detailed examinations of handling and other marketing protocols for both species from point of capture to arrival at continental dealer's premises. Such examinations were made with the help of a number of major dealers in the UK, Spain and France and included studies of handling, packing, holding and transportation methods, physical damage assessments before and after consignment, and chemical and biochemical analyses of seawater and blood samples.Dissolved ammonia levels were found to increase greatly in the fixed volume water of vivier tanks and this was found to be matched by correspondingly high blood ammonia values of the contained animals. The measurement of both free ammonia and ionic ammonia efflux rates of juvenile and adult Cpagurus and Npuber in media with high dissolved ammonia levels was investigated and was found to be related to concentration gradients between the internal and external media. The fluxes could be explained on the basis of diffusion down concentration gradients. When animals were transferred to media with higher ammonia levels than those in blood, a cessation of efflux, or even a net influx of ammonia (NH4+) occurred.During emersion, blood ammonia concentration rose. Such accumulated ammonia was very rapidly off loaded when the animals were re-immersed.The data produced has been discussed in the context of crustacean physiology and of improving the expectations of delivering a live, quality product after journeys of several days.

Of all the corporate tasks facing government agencies and business enterprises, none is more challenging or has received more attention than those involving the management of capital. This is as true for fisheries as any other sector of the economy. However, a fishery is the meeting place of many disciplines and the complex interactions that result from the biological, legal, social, psychological, political, technological and engineering problems within it, intensify the difficulties in the search for ideas and solutions for the rational economic management of capital investment.In spite of the complexities a rational approach is needed involving the location and evaluation of all the opportunities for development across the whole of a fishery now or in the future. Capital investments dictate the entire pattern of production of fish and fish products and decisions taken in this area are usually irreversible. It is therefore, undesirable to allow the situation to develop as a random process.No system of capital budgeting will substitute for the final judgements that have to be made regarding fishery investment decisions. They can provide systematic approaches to reducing available information into patterns that suggest particular decisions'and strategies and an outstanding requirement is to determine in which sectors and to what extent they can assist with these problems.The benefits that can be obtained from the ability to programme capital investments which will secure improvements in the utilisation of capital labour and other resources have not been investigated within a comprehensive framework. A number of theoretical studies have been published and in a few cases have been validated on actual fisheries. Some of them are well developed but have generally considered the problems of sections of the industry in isolation.This thesis is concerned with the development of the methodology; techniques, criteria and data that will assist with management decision-making in this field and, also with an assessment of the relative contributions that result. The particular approach is to consider a completely integrated national fisheries system and investigate the overall problems that develop and then consider the independent sections of fisheries in order to investigate the specific problems that are peculiar to those sections.It is essential for work of this kind, that a theoretical study of the methodology, techniques and criteria should be developed within a realistic environment. For this reason, all the cases examined are based on actual fishery problems.