Trophic relationships of hake (Merluccius capensis Castelnau, 1851 and M. paradoxus Franca 1960) from the Northern Benguela current ecosystem (Namibia) : inferences from stable isotopes and fatty acids

Two species of hake (Merluccius capensis and Merluccius paradoxus) account for most of Namibia’s fisheries catch, and they are important secondary consumers in the Benguela Current ecosystem. Inferences on their trophic relationships have been based mainly on stomach content analyses. However, such data are limited temporally because they represent only snapshots of recent feeding, and are quantitatively biased because of variation in the digestion rates of different prey. The principal aim of the thesis was to understand the trophic relationships of two hake species relative to each other, their known prey and top predators (demersal sharks) in the northern Benguela Current ecosystem (Namibia), using time-integrating trophic biomarkers. By using stable isotope (carbon and nitrogen) and fatty acid signatures of their muscle tissues, my overall objectives were to produce new knowledge about 1) hake ontogenic trophic relationships, 2) the contributions of different prey to hake diets, 3) hake dietary differences, and 4) some aspects of hake’s trophic relationships with demersal sharks. Tissues of hake (n=358), their potential prey (n=455), and demersal sharks (n=42) were collected between 2008 and 2012 during demersal bottom trawl surveys off Namibia, for stable isotope and fatty acid analyses. And more..

Demographic and business features of SMEs in Windhoek, Namibia: implications for bank financing and economic growth

This study examined the demographic and operational attributes of Small and Medium Enterprises (SMEs) in Windhoek, Namibia, and their ramifications for bank funding. The study analysed a sample of 66 small and medium-sized enterprise (SME) owners and operators, focussing on gender, education, age, company experience, yearly income, sector type, and business registration status. Findings indicate a prevalence of female entrepreneurs, a well-educated business populace, and an emphasis on middle-aged business proprietors. The data indicates that although a considerable number of SMEs were in the nascent phases of operation, the majority of enterprises were registered with the Business and Intellectual Property Authority (BIPA). The findings highlighted the capacity of financial institutions (FIs) to offer customised assistance to SMEs, particularly in varied and non-traditional industries, to foster sustainable economic growth in Windhoek. The study finishes with recommendations for banks to enhance services and assess the funding requirements of these enterprises according to their distinct characteristics and challenge

Trophic relationships of hake (Merluccius capensis and M. paradoxus) and sharks (Centrophorus squamosus, Deania calcea and D. profundorum) in the Northern (Namibia) Benguela Current region

The trophic relationships of two hake species (Merluccius capensis and M. paradoxus) and three shark species (Centrophorus squamosus, Deania calcea and D. profundorum) were investigated using nitrogen and carbon stable isotope signatures (15N and 13C) of their muscle tissues. The sharks were more enriched in 15N than the hake, an indication of the apex predator status of sharks. Among the sharks considered, C. squamosus occupied the highest trophic level and fed primarily on benthic prey. The two species of shark from the genus Deania were not different based on 15N or 13C, so they had similar diets. The 13C signatures indicated that M. capensis and sharks fed on prey derived from similar basal resources. However, there was a significant difference in 13C between M. paradoxus and all other species examined, suggesting that they occupied different feeding niches. Isotope-based populationmetrics showed narrower trophic ranges in sharks than M. capensis. Carbon and nitrogen ranges indicated that hake fed on a more diverse pool of carbon sources and had generally more enhanced trophic diversity in their feeding patterns than sharks. Among the species considered, C. squamosus occupied a unique isotopic space. Our results supported the hypothesis there are trophic overlaps among these species, but some interesting differentiation was revealed

Contribution of fish to food and nutrition security in Southern Africa: challenges and opportunities in fish production

This study investigated the role of fish in addressing food and nutrition security challenges in Southern Africa, focusing on 10 countries including Angola, Zambia, Malawi, Mozambique, Namibia, Botswana, Zimbabwe, Lesotho, Eswatini, and South Africa. It examined the current state of food and nutrition security, fish production, and fish consumption patterns. Additionally, the study investigated the challenges and opportunities to enhance fish production in these countries thereby enhancing food and nutrition security. The findings revealed persistent challenges such as a high prevalence of food insecurity and malnutrition throughout the region. Fish production is hindered by overexploitation of fishery resources, inadequate fisheries management, susceptibility to climate-related shocks, limited investments in aquaculture, and inadequate access to input supplies such as quality fish seed and feed. Despite these obstacles, opportunities exist to promote sustainable fish production to enhance food security and nutrition. Countries endowed with extensive coastlines and inland waters exhibit significant potential for fishery development, while landlocked nations are increasingly exploring aquaculture as a viable solution. Addressing the challenges in fish production and capitalizing on opportunities requires comprehensive governance, technological innovation, policy interventions, and investment to ensure the sustainability and resilience of the fisheries and aquaculture industries in the region

A global perspective on the trophic geography of sharks

Sharks are a diverse group of mobile predators that forage across varied spatial scales and have the potential to influence food web dynamics. The ecological consequences of recent declines in shark biomass may extend across broader geographic ranges if shark taxa display common behavioural traits. By tracking the original site of photosynthetic fixation of carbon atoms that were ultimately assimilated into muscle tissues of 5,394 sharks from 114 species, we identify globally consistent biogeographic traits in trophic interactions between sharks found in different habitats. We show that populations of shelf-dwelling sharks derive a substantial proportion of their carbon from regional pelagic sources, but contain individuals that forage within additional isotopically diverse local food webs, such as those supported by terrestrial plant sources, benthic production and macrophytes. In contrast, oceanic sharks seem to use carbon derived from between 30° and 50° of latitude. Global-scale compilations of stable isotope data combined with biogeochemical modelling generate hypotheses regarding animal behaviours that can be tested with other methodological approaches

A global perspective on the trophic geography of sharks

Sharks are a diverse group of mobile predators that forage across varied spatial scales and have the potential to influence food web dynamics. The ecological consequences of recent declines in shark biomass may extend across broader geographic ranges if shark taxa display common behavioural traits. By tracking the original site of photosynthetic fixation of carbon atoms that were ultimately assimilated into muscle tissues of 5,394 sharks from 114 species, we identify globally consistent biogeographic traits in trophic interactions between sharks found in different habitats. We show that populations of shelf-dwelling sharks derive a substantial proportion of their carbon from regional pelagic sources, but contain individuals that forage within additional isotopically diverse local food webs, such as those supported by terrestrial plant sources, benthic production and macrophytes. In contrast, oceanic sharks seem to use carbon derived from between 30° and 50° of latitude. Global-scale compilations of stable isotope data combined with biogeochemical modelling generate hypotheses regarding animal behaviours that can be tested with other methodological approaches.This research was conducted as part of C.S.B.’s Ph.D dissertation, which was funded by the University of Southampton and NERC (NE/L50161X/1), and through a NERC Grant-in-Kind from the Life Sciences Mass Spectrometry Facility (LSMSF; EK267-03/16). We thank A. Bates, D. Sims, F. Neat, R. McGill and J. Newton for their analytical contributions and comments on the manuscripts.Peer reviewe

An attempt at modelling the diets of two sympatric species of hake (Merluccius capensis and Merluccius paradoxus) off the coast of Namibia: Isotope mixing model approach

Two species of hake, Merluccius capensis and Merluccius paradoxus, are the most important secondary consumers in the Benguela current ecosystem. To better understand hake diets in the northern Benguela (Namibia), the stable carbon (13C) and nitrogen (15N) isotope ratios of their muscles, and that of their prey (Hake, n = 115 and prey, n=299) were analysed. Results indicated that their diets were dominated by Plesionika martia, Chlorophthamus agazizi, Myctophids and Euphausiids. The highest contributor to the diet of M. paradoxus varied with length, while the diet of M. capensis was dominated by myctophids at all length classes. Cannibalism accounted for less than 6% and less than 4% in the diets of M. capensis and M. paradoxus respectively. Isotope based estimates of prey dietary contributions differed from that of previous gut content analyses. Overall, the results support the hypothesis that the two species have similar diets. Application of a Bayesian mixing isotope model can be improved to allow for improved hake consumption (i.e. annual) estimates to be made

Analysis of marine aquaculture developments in Namibia. Environmental, economic and legislative considerations

This multidisciplinary analysis of Namibia marine aquaculture developments has found it to have a good potential. Existing Namibian aquaculture laws are comprehensive in nature controlling aspects such as water, land, public health, sanitation and disease, however they ignore fish welfare. Mean temperature of Namibian marine coastal waters in the150 m water depth strata has averaged at 14.07 oC for the last eleven years (1993-2003). The marine waters in the central area of Namibian coastline are colder than the waters both northward and southward. Temperature decreased with water depth at a gradient of about 0.1oC/m in the 100 m water depth strata. Mean salinity averaged at 34.89‰ with low variation in the 100 m water depth column. Species which are considered for aquaculture are ranked on the scale of one to ten according to their respective potentials based on both environmental and economic issues: Oysters (Crassostrea gigas and Ostrea edulis) are ranked at 9/10, Abalone (Haliotis midae) 8/10, Mussels (Mytilus galloprovincialis) 8/10, Rock lobster (Jasus lalandii) 7/10, Rainbow Trout (Oncorhynchus mykiss) 6/10, Hake (Merluccius capensis) with 5/10 and Cobia (Rachycentron canadum) 3/10. Despite the fact that most of the species considered can live within temperature and salinity ranges of Namibian marine coastal waters at different latitudes and depths, their respective farming successes can be enhanced by research to investigate specie-specific conditions that promote their yields. Economically farming of shellfish has better potential than finfish due its low production costs which is partly a result of adjacent nutrient rich Benguela ecosystem and promising investment returns as a result increasing shellfish product demands and prices

Trophic relationships of hake (Merluccius Capensis Castelnau, 1851 and M. Paradoxus Franca 1960) from the Nothern Benguela current ecosystem (Namibia): Inferences from stable isotopes and fatty acids

A thesis submitted in fulfilment of the requirements for the Degree of Doctor of Philosophy (Science)Two species of hake (Merluccius capens is and Merluccius paradoxus) account for most of Namibia's fisheries catch, and they are important secondary consumers in the Benguela Current ecosystem. Inferences on their trophic relationships have been based mainly on stomach content analyses. However, such data are limited temporally because they represent only snapshots of recent feeding, and are quantitatively biased because of variation in the digestion rates of different prey. The principal aim of the thesis was to understand the trophic relationships of two hake species relative to each other, their known prey and top predators (demersal sharks) in the northern Benguela Current ecosystem (Namibia), using time-integrating trophic biomarkers. By using stable isotope (carbon and nitrogen) and fatty acid signatures of their muscle tissues, my overall objectives were to produce new knowledge about 1) hake ontogenic trophic relationships, 2) the contributions of different prey to hake diets, 3) hake dietary differences, and 4) some aspects of hake's trophic relationships with demersal sharks. Tissues of hake (n=358), their potential prey (n=455), and demersal sharks (n=42) were collected between 2008 and 2012 during demersal bottom trawl surveys offNamibia, for stable isotope and fatty acid analyses. Nitrogen isotopes (8 15N) showed a significant positive relationship with size in both M capensis and M paradoxus; however, the correlation slopes of size and 8 15N in the two species were significantly different, with M paradoxus displaying a steeper trophic shift. A significant increase in carbon isotope signature (8 13C) with size was observed in M capensis but not in M paradoxus. In all size classes (except 20-29 em) M capensis had significantly enriched 13C values, generally matching their respective adult shelf-slope distribution. Smaller hake from both species (20-39 em) were trophically indistinguishable, with trophic levels (TL) of3.3 indicating predominant zooplanktivory. The largest M capensis (60-70 em) had TLs of approximately 3.5- 3.6, whereas M paradoxus of the same size. were slightly higher at 3.7-3.8 TL, indicating greater piscivory in the latter. A Bayesian isotope mixing model indicated that teleosts Synagrops microlepsis and Chlorophthalmus agazizi, the shrimp Plesionika martia, myctophids and euphausiids dominated the diets of both hake species. The greatest contributor to the diet of M paradoxus changed depending on the body size of the hake, while the diet of all size classes of M cap ens is was dominated by myctophids. Cannibalism accounted for less than 6% and less than 4% of the diets of M capensis and M paradoxus respectively. Isotope-based estimates of prey dietary contributions differed from those of published accounts of gut content analyses, an indication of overestimation of the time-integrated diet by the latter. The fatty acid (FA) profiles of the two species (M paradoxus and M cap ens is) and potential prey were similar to those typically abundant in marine fish. Palmitic acid (16:0) was the dominant saturated fatty acid (SFA), oleic acid (18: ln-9) was the dominant monounsaturated fatty acid (MUFA) and docosahexaenoic acid (22:6n-3) was the dominant polyunsaturated fatty acid (PUF A) in both hake species. Fatty acid (FA) profiles in the neutral storage lipids of M paradoxus and M capensis were significantly different, an indication of hake species' dietary resource partitioning, although some overlap was apparent. There was a significant temporal effect on hake FA compositions, reflecting temporal variations in quantity and quality of dietary resources. Feasible contributions of hake to the diets of three demersal sharks indicated that hake are not major prey of Centrophorus squamosus, whose diet was dominated by crustaceans. However, there was an increased contribution of hake to the diets of Deania sharks. All three sharks studied (Deania calcea, D. profundorum and C. squamosus) potentially consumed upwards of 18 % (208 960 tonnes per year) of the hake biomass [2011 hake biomass estimates (1111 196.8 tonnes)]. The two Deania species were isotopically indistinguishable in terms of 815N, and fed on a prey composition that overlapped with that of M paradoxus. 813C values indicated that hake and sharks fed on prey from similar basal resources, with C. squamosus being significantly different from M paradoxus but not from M capensis. The range of 813C and 815N indicated that the two hake species had a higher range of carbon sources as well as enhanced trophic diversity in their feeding patterns than did the three shark species. This study is the first combined usage of stable isotope and fatty acid techniques to analyse trophic relationships of M capensis and M paradoxus in the northern Benguela Current (Namibia). The study contributes towards understanding of trophic interactions in Namibian waters, and can aid the implementation of a science-based ecosystem approach to fisheries management in the Northern Benguela Current region (Namibia). The extension of this analysis throughout hake distribution ranges will provide additional insights into the trophic dynamics of hake species in future, and my study represents a solid foundation from which to develop such extensions