Thesis (M.Sc.-Res.)--University of Wollongong, 2007. / Typescript. Includes bibliographical references: p. 69-83.

Thesis (M.Sc. (Ichthyology & Fisheries Science)) - Rhodes University, 2008.

Thesis (Ph.D.)--Memorial University of Newfoundland, 2002. / Bibliography: leaves 11-1-11-48.

Thesis (M.Sc.)--Memorial University of Newfoundland, 1999. / Restricted until November 2001. Includes bibliographical references.

Thesis (M.Sc.)--Memorial University of Newfoundland, 2003. / Bibliography: leaves 88-93. Also available online.

The panga, Pterogymnus laniarius (Cuvier, 1830), is a South African endemic sparid fish species. On the Agulhas Bank, South Africa it is a commercially important species, caught as bycatch in the hake directed trawlfisheries and targeted by offshore hook-and-linefishers. Recently there has been considerable interest shown in directing further fishing effort on this species. The lack of a suitable management procedure for teleost bycatch in South Africa was the principal reason for undertaking this study. This thesis investigates aspects the panga's life history, particularly those aspects that have management implications. A full knowledge of this species' distribution and abundance was necessary as this could highlight the existence of any nursery areas, ontogenetic migratory patterns and areas of high spawner biomass. The derived parameter estimates were then included as inputs into stock assessment models to determine the status and productivity of the resource. Growth studies based on sectioned sagittal otoliths revealed that the panga was a relatively slow growing fish with ages of 16 years being recorded. Growth was best described by the von Bertalanffy growth model as Lt=379.4(1-e⁻°·¹³⁽t ⁺ ¹·⁷⁸⁾). Total, natural and fishing mortalities were estimated at 0.36 year⁻¹, 0.28 year⁻¹ and 0.08 year ⁻¹, respectively. Detailed histological examination of the gonads revealed that panga is a late gonochorist, males and females maturing after a non-functional intersexual stage. Females mature at approximately 200 mm fork length or 4 years of age. Reproduction occurs throughout the year although there is a slight peak in winter. Gametogenesis was found to be similar to that of other sparid fishes and marine teleosts in general. The panga feeds predominantly on crustaceans with a distinct ontogenetic shift in feeding habits. Juvenile fish feed predominantly in the water column on mysids after which they move to the benthos. Subadult fish feed principally on ophiuroids and amphipods. Adult fish remain on or near the benthos, feeding predominantly on crabs, and on polychaetes, ophiuroids and fishes to a lesser extent. Several aspects of the panga's biology contribute to its ability to sustain a higher fishing pressure than other sympatric sparid species. These include its late gonochoristic reproductive style, protracted spawning season, maturation before recruitment and preference for soft substratum prey that enables it to utilise large areas of the Agulhas Bank. The panga's longevity, slow growth and low natural mortality rate, however, mitigated against these factors and were considered in the stock assessments. A heterogeneous Geographical Information System (GIS) was developed to analyse the distribution and abundance patterns of the panga. The GIS developed in this thesis makes a significant contribution towards the development of a South African Fisheries Information System to analyse and manage fish resources in general and bycatch resources in particular. The GIS developed in this study combines statistical Generalized Additive Modelling and standard GIS methods. Analysis of fourteen biannual fishery independent biomass surveys, disaggregated by life history stage, revealed that a nursery area for immature fish (<23 cm TL or < 4 years of age) exists on the Central Agulhas Bank. After sexual maturation, approximately 40% of the biomass migrated eastwards, colonising large areas of the Eastern Agulhas Bank.ilie location of the nursery area appears to be a result of the pelagic eggs and larvae being advected towards the coast in an anti-cyclonic gyre, stemming off the Agulhas current and later deposited over the Central Agulhas Bank. The weak bottom currents on the Central Agulhas Bank prevented juvenile loss to the Benguela system. The eurytopy of adult fish to various physical variables such as temperature, dissolved oxygen and stronger currents enabled it to reduce conspecific competition and migrate eastwards with distribution primarily determined by depth. Relative biomass estimates revealed a gradual increase in biomass of 5.5% per annum between 1988 and 1995. Predictions from yield-per-recruit, biomass-per-recruit and spawner biomass-per-recruit analyses showed that there was scope for further exploitation. A FSB₅₀ fishing strategy was considered to be the most appropriate fishing strategy as it did not reduce the spawner biomass-per-recruit to less than 50% of unexploited levels. Effort control was considered the most effective management tool as the age-at-50%-selectivity occurred after age-at-sexual maturity and releasing undersized fish was undesirable due to heavy mortalities resulting from severe barotrauma. The panga resource was also assessed using an age-structured production model. The values for the free parameters of the model were estimated using biomass indices derived from fishery-independent trawl surveys. Although the data were fairly uninformative about the productivity of the resource, the results indicated robustly, that the population has recovered from low levels in the mid-1970's and could sustain higher levels of fishing intensity. Risk analysis calculations were used to assess the sustainability of different catch scenarios. The level of sustainable catch was found to be sensitive to the selectivity pattern of the gear utilised. Both stock assessment methods used in this study to investigate the status of the panga resource showed that the resource could theoretically sustain higher catches. It was found that although the stock could be harvested using available fishing methods, the sympatry of this species with other commercial species was of concern as the latter would form a significant bycatch in a panga directed fishery. The failure of current harvesting methods to address the bycatch problem highlights the management problem in South Africa and stresses the need for creativity by both scientists and fishers in designing new and improved methods for selectively harvesting bycatch fish resources. Considering that no suitable method is currently available to fish the panga stock in a directed fishery the fishery should be managed as status quo until some suitable and efficient gear is developed.

<p>With the increasing global population, providing sufficient food to meet the rising demand has become a great challenge to food-producing sectors. Aquaculture is one of the food sources which produces varieties of seafood. Shrimp is the most popular seafood in the US, and its production plays an important role in the aquaculture industry. However, shrimp farming causes various types of pollution to damage the environment and aquatic biodiversity, the associated impacts must be mitigated to ensure the sustainability of shrimp production. This study performed a life cycle assessment (LCA) on different shrimp production chains from cradle to the market in Midwestern US covering three farming systems and eight shrimp feed formulas. Midpoint environmental impacts including acidification potential (AP), eutrophication potential (EP) and global warming potential (GWP) were determined. Feed production was identified as the main contributor to the AP and GWP for both the intensive and semi-intensive production systems (SPS), regardless of the feed formula. While the environmental performance of feed production highly depended on the feed conversion ratio, feed ingredient was another determining factor in which animal protein sources, including poultry by-product meal and fishmeal, showed high contributions to the AP and GWP. However, plant proteins such as soybean, wheat, and corn gluten meals produced higher EP, therefore, substituting plant-based ingredients for animal-based ones in shrimp feeds did not all result in positive environmental consequences. Shrimp farming was the hotspot of all the three impacts, especially accounting for the highest EP. Among the three farming systems studied here, the SPS caused the highest environmental burdens due to the intensive uses of chemicals and fertilizers. On the contrary, the extensive farming was found to be the most sustainable system because no inputs of feeding and additional materials and energy are required for its operation. The LCA model developed in this study is expected to serve as US shrimp farmers’ decision-making guidelines to adapt farming practices with lower environmental footprint.<br><a></a></p>

Globally, the status of many fish stocks remains unknown, of which the majority fall under data-limited small-scale fisheries. Management decisions in most of these fisheries are difficult due conflicting objectives and views from fisheries managers and scientists. In South Africa, the traditional boat-based ‘linefishery’ provides such an example of a small-scale, multi-species fishery with a long history. The historical de facto open access nature of this fishery resulted in continuous declines in catches of many linefish species, and in 2000 the fishery was declared to be in a state of emergency. This led to a reduction of up to 70% within the fishery, among other measures, such as introductions of size and bag limits. Assessing the status of linefish species is difficult due to a lack of reliable long-term data for the majority of species. The aims of this study were therefore: (1) to quantify the stock status for all linefish species with available life history and size composition information, (2) compare current and historical stock levels to ascertain if the reduction in effort facilitated any recovery in linefish species and (3) correlate the current stock status estimates to life history traits to identify simple indicators of resilience to exploitation. For this purpose, length frequency data from 1988-1990 and 2008-2010 and biological parameters sourced from literature were used to conduct per-recruit analysis to estimate spawner biomass depletion (SBD) for both time periods. The majority of the 26 species analyzed, (68%) showed improvements in spawner biomass between the two time periods, with 12 species undergoing a change in stock status (i.e. improving from collapsed or overexploited). Specifically, increases in length-at-capture (Lc) as well decreases in fishing mortality (F) facilitated recovery for many species. Asymptotic length (L∞), as well as the ratio between Lc / L∞ and Lc / Lopt (where Lopt is the optimum length) were found to be significantly correlated to spawner biomass depletion. Kruskal Wallis analyses revealed that only movement pattern had a significant relationship to SBD, more specifically, migratory species were significantly more depleted than resident ones. This study identifies simple indicators that, in the absence of conventional stock assessments, provide fisheries managers with a fundamental understanding of a species’ susceptibility to overexploitation – offering another decision making tool for use in data poor fisheries such as the South African linefishery.

Stock assessments are statistical models which characterize the state of a population of fish. Data for stock assessment models of West Coast nearshore groundfish come largely from fisheries-dependent sources. Incorporating fisheries-independent data would increase data availability. A potential source of fisheries-independent data which is comparable to existing fisheries-dependent data is the California Collaborative Fisheries Research Program (CCFRP), a Marine Protected Area (MPA) monitoring study. We are interested in understanding the context in which CCFRP could be implemented into assessments of nearshore groundfish, specifically rockfish. To investigate this, we used management-relevant metrics to examine three questions concerning the implementation of CCFRP as a data source: whether the scope of the project captures the core depth distribution of a species, whether the methodology of the project affects assessment metrics, and how the presence of data from MPAs affects assessment metrics. Comparisons were made for three species with different life histories and desirability in the recreational groundfish fishery: Blue rockfish (Sebastes mystinus), Vermilion rockfish (S. miniatus), and Gopher rockfish (S. carnatus). Based on these metrics and comparisons, we found that the specific method of potential implementation of fisheries-independent data into stock assessments is highly species dependent, but all species could benefit. Implementing this data will lead to better-informed management, ensuring that these populations persist.

Blue Catfish were introduced in the tidal tributaries of the Chesapeake Bay in the 1970s and 1980s to establish new fisheries during a time period when many fisheries were in decline due to pollution, habitat alteration, disease, overfishing, and environmental catastrophes. Having expanded their range to most Bay tributaries, the species has drawn concern from many stakeholders and scientists for its effects on at-risk and economically important native and naturalized species. My study focused on understanding the dynamics of this species based on multiple long-term monitoring data and evaluating potential management strategies to meet stakeholder needs. I sought to understand how is growth variability was partitioned over time and space, how Blue Catfish populations changed from 1994 to 2016, and how predation on native species and fishery-based performance measures may respond to management intervention. As Blue Catfish length-at-age is exceptionally variable in Virginia tributaries of the Chesapeake Bay, I evaluated the variability in growth using candidate non-linear mixed effects models that described variability in growth over time and space. Linear trend tests supported declines in growth over time within river systems, but did not support the presence of synchronous growth responses among river systems. To better understand population dynamics of Blue Catfish in the Chesapeake Bay watershed, I developed a statistical catch-at-length model for the James River to estimate population size, instantaneous fishing mortality, and size structure over time. The statistical catch-at-length model estimated that Blue Catfish abundance increased slowly and peaked in the mid-2000s before undergoing a recent decline. The model estimated a large spike in abundance due to an estimated large recruitment event in 2011, but may be an artifact of missing data in 2012 in both relative abundance indices examined. The newly developed statistical catch-at-length model provides most detailed information on population dynamics of Blue Catfish in the James River and can be expanded and updated as new data become available. Based on results of the statistical catch-at-length model, I examined population responses to unregulated, maximum length limit (60 cm), and harvest slot limit regulations (harvest allowed 25 –60 cm) in a management strategy evaluation framework. The management strategy evaluation supported that the James River Blue Catfish population could be reduced with increased harvest, but trophy-size fish would decline. Consequently, fishery managers tasked with invasive species management must consider this tradeoff of fishery economic benefits and predation on native populations, especially those prey in which population sizes are unknown. / Doctor of Philosophy / Blue Catfish are non-native to the Chesapeake Bay watershed, but were stocked in the 1970s and 1980s to provide fishing opportunities to the region. Unknowingly, Blue Catfish expanded downstream and beyond the boundaries of the rivers to which they were originally stocked and now exist in extremely dense populations in places. This expansion in population size and distribution has generated concern for the health of the Chesapeake Bay and calls for population control. I wanted to learn more about Blue Catfish in Virginia, specifically Blue Catfish growth rates, population dynamics, and how they might respond to control efforts. I examined Blue Catfish growth rates and found growth rates differed over time and across river systems. Blue Catfish tended to grow more slowly over time as their populations matured. As growth rates declined, population size increased with maximum population sizes in the late 2000s in the James River with a subsequent decline in abundance. Many invasive species exhibit this sort of phenomenon, where population sizes increase and reach a maximum before declining. Finally, I looked at Blue Catfish responses to different fishing regulations and harvest levels, finding that increased harvest could help control Blue Catfish population sizes. However, Blue Catfish management objectives are in conflict as regulations that limit predation of native species of interest also reduce the proportion of large fish in populations. Blue Catfish management will require stakeholder-driven approaches to ensure buy-in and reduce user conflicts.