Browsing by Author "Armstrong, M J"

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    Birthdate distribution of juvenile anchovy, Engraulis capensis caught in the Southern Benguela ecosystem
    (Elsevier, 1992) Waldron, M E; Armstrong, M J; Roel, B A
    Birthdate distributions of anchovy recruits caught during research surveys in June 1985 and June 1989 were compiled from weighted length frequency distributions, aged samples and length frequencies from commercial catches. Birthdates ranged from July to March with a peak in October for both year-classes. However, birthdate distribution for the 1989 year-class showed comparatively few fish spawning after October 1988. Also, the growth rate of recruits was slower in 1989 than in 1985. It is proposed that the very weak 1989 year-class of anchovy and the low spawning biomass subsequently observed were a result of poorer-than-average egg production and survival of prerecruits spawned after October 1988, and the slow rate of growth of juvenile anchovy recruited till June 1989.
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    Growth of juvenile round herring Etrumeus whiteheadi in the Benguela system
    (National Inquiry Services Centre (NISC), 1991) Waldron, M E; Prosch, R M; Armstrong, M J
    The clupeoid Etrumeus whiteheadi, known locally as the round herring, is an important component of the commercial purse-seine catch off South Africa. Three methods are employed to estimate the growth of juvenile round herring: examination of annual hyaline rings on fish otoliths, examination of daily growth increments on the otoliths, and analysis of length frequency distributions. The results show that fish smaller than 120 mm are less than one year old and that analysis of daily growth increments is unreliable for bigger fish. The problems of determining the age of fish on the basis of counts of the number of hyaline rings is also addressed by reference to a model which can be applied to any species with a protracted spawning period.