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    Distribution, feeding behaviour, and condition of Cape horse mackerel early life stages, Trachurus capensis, under different environmental conditions in the northern Benguela upwelling ecosystem (2015)
    Oxford University Press
    Details
    Publication Date: 2015-01-20
    Description: Early life history (ELH) traits are key to understand variable recruitment success and hence the stock size of marine fish. One of the currently most puzzling ecosystems in this regard is the northern part of the Benguela Current upwelling system off Namibia. Here, populations of the formerly dominant pelagic species, sardine and anchovy, failed to recover during the last three decades after a dramatic decline. In contrast, Cape horse mackerel, Trachurus capensis , maintained a constant population size. Warming of the system and shoaling of hypoxic zones together with feedback loops within an altered foodweb are discussed to be responsible for this regime shift. In this study, we address the role of larval traits for the successful performance of the T. capensis population under the present environmental conditions with the focus on feeding ecology. We investigated seasonal variations of the geographical distribution, growth rate, feeding ecology, and nutritional condition of their ELH stages and examined relationships with water temperature, dissolved oxygen concentration, and micro-zooplankton composition. T. capensis' ELH stages showed a wide spatial and seasonal distribution, a preference for higher water temperatures (18–21°C) and presence over a wide range of dissolved oxygen concentrations (0.13–6.35 ml O 2 l –1 ). Feeding success was high and mainly different groups of Copepoda were targeted, which were strongly size selected. The high dietary importance of micro-copepods during large parts of the larval phase indicates successful exploitation of this food source, which has increased in abundance during the last decade. It also explains observed best nutritional conditions at temperatures between 18 and 21°C, since these small copepods are commonly associated with warmer temperatures. Altogether, these traits enhance the species' probability to encounter suitable environments for the survival of their ELH stages, which is likely to lead to their high recruitment success in the northern Benguela ecosystem.
    Print ISSN: 1054-3139
    Electronic ISSN: 1095-9289
    Topics: Biology , Geosciences , Physics
    Published by Oxford University Press
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  • 2
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    Characteristics of survivors: growth and nutritional condition of early stages of the hake species Merluccius paradoxus and M. capensis in the southern Benguela ecosystem (2012)
    Oxford University Press
    Details
    Publication Date: 2012-04-10
    Description: Grote, B., Ekau, W., Stenevik, E. K., Clemmesen, C., Verheye, H. M., Lipinski, M. R., and Hagen, W. 2012. Characteristics of survivors: growth and nutritional condition of early stages of the hake species Merluccius paradoxus and M. capensis in the southern Benguela ecosystem. – ICES Journal of Marine Science, 69: 553–562. Larval mortality in marine fish is strongly linked to characteristic traits such as growth and condition, but the variability in these traits is poorly understood. We tried to identify the variability in growth in relation to conditions leading to greater survival chances for early stages of Cape hake, Merluccius paradoxus and M. capensis , in the Benguela upwelling ecosystem. During two cruises in 2007 and one cruise in 2008, hake larvae and juveniles were caught. Otolith microstructures revealed a larval age ranging from 2 to 29 days post-hatching (dph), whereas juvenile age was 67–152 dph. RNA:DNA ratios, used to evaluate nutritional condition, were above the relevant threshold level for growth. No strong coupling between growth and condition was detected, indicating a complex relationship between these factors in the southern Benguela ecosystem. Merluccius paradoxus juveniles caught in 2007 (the surviving larvae of 2006) had significantly higher larval growth rates than larvae hatched in 2007 and 2008, possibly indicating selection for fast growth in 2006. High selection pressure on growth could be linked to predation avoidance, including cannibalism.
    Print ISSN: 1054-3139
    Electronic ISSN: 1095-9289
    Topics: Biology , Geosciences , Physics
    Published by Oxford University Press
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
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