Volume 7 (ISTJN)

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http://hdl.handle.net/11070/1750

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Browsing Volume 7 (ISTJN) by Author "Iitembu, Johannes A."

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    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
    (University of Namibia, 2016) Iitembu, Johannes A.
    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.
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    Trophic relationships of three deep-sea crustacean species (Aristeus varidens, Plesionika martia and Funchalia woodwardi) off Namibia
    (University of Namibia, 2015) Endjambi, Tobias; Iitembu, Johannes A.; Nashima, Festus P.
    Trophic ecology of deep-sea crustaceans in the marine waters off Namibia is not well understood, although they form part of diets of important commercial species off Namibia. Study of their trophic relationships enhances our understating of the functioning of marine food webs and avail information needed for consideration of trophic interaction in fisheries management decisions. This study aimed at investigating the trophic relationships of striped red shrimp (Aristeus varidens), golden shrimp (Plesionika martia) and Woodward’s pelagic shrimp (Funchalia woodwardi) using stable isotope (nitrogen 15N) measurements of their muscle tissues. Samples were collected during the 2010 annual hake biomass survey off Namibia. Significant differences were observed in the mean trophic levels and nitrogen (15) measurements of the three species. Funchalia woodwardi showed a negative linear relationship between size and 15 and between depth and 15. Aristeus varidens and P. martia showed no significant linear relationship between 15 and depth or size. This work is the first to examine trophic relationships of the three deep sea crustaceans in the Northern Benguela current ecosystem using stable isotope analysis.