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A problem commonly encountered in stock assessments of tropical marine resources in developing countries is data paucity, which invariably results from the lack of both human and economic capacity within the government to implement and maintain programmes for data collection and analysis. With special reference to the demersal fishery of Brunei Darussalam, this thesis examines approaches for extracting useful information from data-poor fisheries to assess the state of resources and inform fishery management actions. By using official fishery statistics, augmented by local ecological knowledge (LEK) obtained from fishers engaged in either the large-scale (LS) or small-scale (SS) fisheries in Brunei, changes in demersal fishery resources over the years were assessed. The sustainability of Brunei’s demersal capture fishery was evaluated in the face of its ongoing development and climate change. Using trophodynamic indicators such as mean trophic level (MTL), Fishing-in- Balance (FiB), trophic spectra (TS) and community structure analyses, LS fishery catches of Brunei between 2000 and 2009 revealed a deteriorating state of the coastal demersal ecosystem. Closer examination of the abundance of overall demersal finfish stocks, using the Catch-Per-Unit-Effort (CPUE) index – standardised for other factors not related to abundance – indicated a declining trend, even when total catches remained stationary, although trends in abundance of the different demersal fish families varied. This rapid significant change in recent years is further supported by fishers’ LEK on relative abundance of Brunei marine resources. The study on LEK has also revealed the ‘shifting baseline syndrome’ (SBS) among currently active fishers and their exploited populations, a phenomenon not previously reported for Brunei fisheries. Findings from the study are synthesised with other information, where a number of key issues and policy options are discussed, and recommendations for the management of the fishery are made. This thesis demonstrates that researchers in data-poor fisheries can utilise different assessment tools, given the resources at their disposal, to assist in the management of marine resources.

published_or_final_version / Zoology / Master / Master of Science

The purpose in this thesis was to undertake a bioeconomic analysis of the fisheries of the English Channel. An economic survey of the fishery was undertaken to establish the economic and financial performance of the various fleet segments in the fishery in 1994-95. It was found that the fishery as a whole was producing negligible levels of resource rent, although some boat owners were receiving intra-marginal rents. Long run equilibrium models of sole and plaice were developed and the optimal (profit maximising) level of effort (in beam trawl hours equivalent) was estimated. It was found that the optimal level of effort was substantially lower than the current level of effort expended on these two species. A method for estimating surplus production models which incorporate decreasing returns to effort was also developed and applied to the fishery. A linear programming (LP) model was also developed which incorporate the multi-species and multi-gear features of the fishery. The model was used to estimate the maximum level of profits that could be achieved in the fishery given existing stock conditions. It was found that profits could be increased substantially, but at the cost of a large reduction in fishing employment. A compromise `optimal' was estimate using multi-objective (goal programming) techniques. The LP model was also used to estimate the effects of a restriction on days at sea and reduced total allowable catches of sole and plaice. It was estimated that these policies would impose additional costs on various segments of the fishery, particularly the trawl segments to which they are targeted. Benefits, if any, were likely to be negligible as the policies were estimated to result in increased discarding rather than decreased catch. The model results suggest that the long term level of effort may be more effectively reduced through implementing a charge on access to, or use of, the resource.

<p> In Arctic Alaska, Dolly Varden <i>Salvelinus malma </i> is highly valued as a subsistence fish; however, little is known about oceanic dispersal or ecology. This study addresses this knowledge gap, by using a fisheries independent method, pop-up satellite archival tags (PSATs). In spring of 2012 and 2013, we attached 52 PSATs to Dolly Varden in a river in northwestern Alaska, which flows into the Arctic Ocean, to examine the marine dispersal, behavior and habitat occupancy of this species. Tagged Dolly Varden demonstrated two types of dispersal, including offshore and nearshore dispersal. The offshore type was the first documented northwesterly dispersal and occupancy of Outer Continental Shelf (OCS) areas of the Russian Chukchi Sea. While occupying this area, tagged Dolly Varden demonstrated affinity for the first 5 m of the water column, diel patterns in depth occupancy, and dive depths of up to 50 m, while experiencing a thermal environment of generally 3&ndash;7&deg;C. During the nearshore dispersal type, Dolly Varden transited in coastal areas of northwest Alaska, likely returning to their natal rivers to spawn. While in nearshore areas, tagged Dolly Varden always occupied shallow waters (&lt; 6 m), and experienced a rapidly changing thermal environment (&plusmn; 15&deg;C), including some waters temperatures cooler than -1&deg;C. This study demonstrates that PSATs offer an alternative and effective platform with which to study several aspects of large adult Dolly Varden dispersal and ecology in areas where it is not practical or feasible to capture these fish, such as in coastal and offshore regions of Arctic Alaska. Additionally, the results of this study have increased our knowledge of the summer marine distribution, behavior and thermal environment of Dolly Varden in Arctic regions of Alaska, and this knowledge is important to several stake holders for the conservation of this important subsistence species.</p>

<p> Arctic Grayling (<i>Thymallus arcticus</i>) are widely distributed on the Arctic Coastal Plain (ACP) of Alaska, and are one of the few upper level consumers in streams, but the trophic pathways and food resources supporting these fish are unknown. Grayling migrate each summer into small beaded streams, which are common across the landscape on the ACP, and appear to be crucial foraging grounds for these and other fishes. I investigated prey resources supporting different size classes of grayling in a beaded stream, Crea Creek, where petroleum development is being planned. The specific objectives were to measure terrestrial prey subsidies entering the stream, quantify prey ingested by Arctic Grayling and Ninespine Stickleback (<i>Pungitius pungitius </i>), determine if riparian plant species affect the quantity of terrestrial invertebrates ingested by grayling, and determine if prey size and type ingested were a function of predator size. Results indicated that small grayling (&lt; 15 cm fork length (FL)) consumed mostly aquatic invertebrates (caddisflies, midges, and blackflies) early in the summer, and increasing quantities of terrestrial invertebrates (wasps, beetles, and spiders) later in summer, while larger fish (> 15 cm FL) foraged most heavily on stickleback. Riparian plant species influenced the quantity of terrestrial invertebrates entering the stream, however these differences were not reflected in fish diets. This study showed that grayling can be both highly insectivorous and piscivorous, depending upon fish size class, and that both aquatic and terrestrial invertebrates, and especially stickleback, are the main prey of grayling. These results highlight the importance of beaded streams as summer foraging habitats for grayling. Understanding prey flow dynamics in these poorly studied aquatic habitats, prior to further petroleum development and simultaneous climate change, establishes essential baseline information to interpret if and how these freshwater ecosystems may respond to a changing Arctic environment. </p>

The fisheries resources of Lake Victoria support the livelihoods to the lakeside rural communities and are vital to the economies of Kenya, Tanzania and Uganda, especially through fish exports. Management decisions to enable long-term sustainable exploitation of these fisheries require appropriate knowledge of the fishing effort and catch statistics, as these are pertinent for evaluating the fish stocks and future prospects of the fishery. Catch assessment programmes in the Ugandan part of the lake, which should provide this type of information, collapsed in the late 1980s. This study evaluated the current status of fishing effort and fish catches and their implications for the management of the fisheries in the Ugandan part of Lake Victoria. Historical trends in fishing effort and fish catches, total fishing effort in 1990 and 2000, and the current status of fish catch-effort, in the Ugandan part of the lake, were examined.

The prevalence of Penaeus monodon baculovirus (MBV) in black tiger prawn (Penaeus monodon Fabricus) was investigated based on 372 diagnostic cases examined from October 1989, to December, 1990. Laboratory transmission of MBV to the different life stages of P. monodon and tolerance of MBV in infected hepatopancreatic tissues to chemicals and extreme environmental conditions were studied. A comparative assessment of the growth performance, survival and food conversion ratio between MBV-infected and non-infected populations of P. monodon was investigated and a new technology called Strategic Egg Prophylaxis (SEP) in the production of MBV-free P. monodon postlarvae was developed and tested. MBV was the most prevalent viral disease of P. monodon accounting for 67.1% of all diseases diagnosed in this species, and was widely distributed in all 12 major shrimp farming provinces in the Philippines throughout the year. The nauplii and zoea larval stages were refractory to MBV infection within 12 days post inoculation, but the mysis larval and the postlarval stages were susceptible to MBV infection within 6 and 2 days post inoculation, respectively. Cumulative mortality was significantly different (α = 0.05) between the MBV-infected and unexposed control groups of mysis larval and postlarval test shrimps. No significant growth rate differences were observed between the MBV-infected and unexposed control groups of larvae and postlarvae. MBV was resistant to 150 ppm iodine, 1:100 dilution of peroxygen/organic acid compounds and 10 ppm calcium hypochlorite at 240, 240 and 480 min of exposure, respectively, and to freshwater and at 37°C for 240 min. Direct exposure to sunlight for 240 min inactivated MBV in the hepatopancreatic tissues. In pond cultured P. monodon populations, the MBV negative stocks grew by as much as 43.4%, 20.8%, 13.7% and 13.7% more than the MBV-infected stocks at densities of 30/m², 20/m², 18/m², and 10/m², respectively over a 126 day growing period. Mortality was significant in MBV positive stocks affected with protozoan and bacterial shell disease. Food conversion ratio (FCR) was not a significant factor among MBV negative and the MBV infected populations. MBV negative P. monodon postlarvae were successfully produced using the Strategic Egg Prophylaxis (SEP) by washing and rinsing P. monodon eggs with iodine, benzalkonium chloride, calcium hypochlorite or ozone-treated seawater. The eggs washed with ozonized and benzalkonium chloride-treated seawater gave higher hatching rates of 72.4% and 60.3%, respectively. Postlarval survival at PL-7 was 67.6% in eggs washed with ozonized seawater and 42.3% in benzalkonium chloride-treated seawater. The unwashed control groups developed MBV infections starting at PL-7 stage.

Cholla Lake is a cooling reservoir for the coal-fired Cholla electrical generating plant. The lake provides recreational fishing and water contact recreation. The fish populations are self-sustaining. I collected water, sediment, and whole body fish samples to be analyzed for levels of some possibly toxic inorganic constituents. I also measured dissolved oxygen, pH, Secchi disk transparency. I compared current fish population structure, fish stomach contents, and the frequency of occurrence of benthos, with those same parameters in previous studies. Water temperature and turbidity have increased; catfish and bluegill have increased in their relative abundance; and the density of benthic invertebrates has decreased. Aquatic insects occur most commonly in the stomach contents of bluegill and filamentous algae in the stomachs of catfish. Selenium levels in all matrices exceed national averages and are above levels in a nearby reservoir unaffected by the power station.