A windows based computer program to compute fish back-calculated lengths at age was created using Visual Basic 6.0© programming language. The objective of this project was to develop a computer program that is user-friendly and requires minimal user input to produce back-calculations. This program incorporates the familiar windows based graphical user interface and can compute up to 10,000 fish with a maximum age of 50 years. The input data can be imported from an Excel spreadsheet or manually entered directly to the program. Back-calculated lengths were computed using the traditional Lee method [ (L; = a + [ (L, - a) ( S; / Sc ) ]. Additional related statistical outputs are also included. The output data can be viewed using Excel where it can also be formatted for individual use. The program was compared with DisBcal using yellow perch age and length data. Results of the comparison were nearly identical with differences due to a rounding function of the output data. / Department of Biology

This thesis investigates agrarian transitions within aquarian contexts by investigating livelihood transitions in a small rural fishing village in central Vietnam. Examined are powers at play that inform livelihood transitions as fishers and fish farmers respond by moving in and out of different production systems in order to maintain their fishing and fish farming livelihoods. This research reveals that aquarian transitions in Vietnam could follow a similar trajectory of agrarian transitions whereby smaller, less efficient production systems make room for more efficient economies of scale. In conducting a thorough and detailed empirical analysis of production systems, the socio-economic relations that shape production systems, and natural resource governance within the Vietnamese context, this research contributes to a better understanding of the knowledge surrounding fishery resources and livelihood options.

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.

<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.

Cormorants are piscivorous birds with a daily food intake (DFI) of approximately 500 g. They are a protected species under the Wildlife and Countryside Act 1981. In the UK, the number of over-wintering, inland cormorants increased steadily between 1970 and 1987, at a rate of between 5 and 10 % per annum. An increase of 74 % occurred between winter 1987/88 and 1990/91, and the population is still believed to be rising. The population growth was observed in all regions of the UK, on all habitat types. As cormorants exploited new habitats, ornithologists welcomed their increased presence. This contrasts with the views of angling bodies, who assert that the presence of cormorants, feeding daily on their fisheries, has a damaging impact on fish stocks with inevitable financial losses. Due to a lack of effective non-lethal control methods, the angling bodies wish to see the cormorants removed from the protected species list so their inland numbers can be controlled. Ornithologists insist that there is no scientific evidence proving cormorants are damaging to inland fisheries and so are opposed to any culling. A review of previous cormorant studies was undertaken to evaluate information on their ecology, feeding behaviour and predation impact. The general conclusion was no study had been able to prove cormorant predation damages fish populations, because few studies had moved beyond determining the mass of fish removed by the birds over the particular study period. No assessment had been made of the impact of that fish removal on the fish population dynamics and the angling performance of the fishery. This highlighted the requirement for research into the impact of cormorant predation on inland fisheries. This study was formulated to estimate cormorant predation impact on fisheries in a more realistic and robust manner than had previously been undertaken. The principal objective of the study was to integrate fish population and cormorant feeding dynamics data on specific fisheries (study sites) in such a way as to quantify, where possible, the full impacts of the cormorant predation. This required the following criteria at each study site: - evaluation of the historical status of fish and cormorant populations; - determination of the population and community dynamics of the fish stocks; - analysis of the angling effort and angling performance; - identification of the species, and estimation of the numbers and sizes of fish consumed and wounded by cormorants, and comparison with the numbers and sizes of the fish populations present; - determination of the occupancy on, and use by, cormorants at the selected sites. The work programme ran between September 1995 and July 1998, covering three winters of cormorant predation. At each study site, the cormorant feeding dynamics were assessed by detailed feeding observations and cormorant counts. This enabled data to be collected on the species, size and amount of fish being ingested during each foraging bout, and the diurnal and seasonal patterns of cormorant occupancy. As feeding observations were unable to completed at each site everyday, a modelling system was designed, using a Monte Carlo Simulation (MCS), to estimate the number and mass of fish being removed from the site over the whole winter period. The fisheries data were collected by electric fishing, seine netting, hydro-acoustics and angler catch analysis. The actual methods used at each site were dependent upon the physical conditions present. The data were analysed for fish population dynamics, including length frequency of species, year class strength, natural mortality rate and growth indices; and for angling performance, including catch per unit effort and the relative importance of species. Combining site-specific data for the fish species composition, and the length frequency distribution from fisheries surveys and the cormorants' diet, allowed preliminary predation impact assessment. Reconstruction of life tables from the fisheries data allowed integration of the cormorant feeding data from the Monte Carlo Simulation to assess impact in terms of the numbers of fish consumed on subsequent population densities. This enabled the status of the fish population at each study site to be shown, with and without cormorant predation over the three-year period, resulting in a detailed predation impact assessment. The fisheries studied were located in two regions of the UK, the Midlands and the North West of England. This enabled the research to be completed in two distinct geographical areas, with known and established over-wintering cormorant roosts. The Midland study sites were Holme Pierrepont Rowing Course, Colwick Park Trout Lake and the River Trent. The North West study sites were the lower River Ribble and Grimsargh number 3 Reservoir. These sites encompassed cyprinid and salmonid fish populations, and covered riverine and lacustrine fisheries.

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.