Browsing by Author "Champion, Harold"

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    Acoustic investigation of the shoaling dynamics of sardine sardinops sagax populations : implications for acoustic surveys
    (1997) Coetzee, Janet Claire; Field, John G; Champion, Harold
    The total allowable catches (TA Cs) of both anchovy and sardine in South Africa are determined by assessment methods which rely on absolute estimates of recruitment and spawner biomass each year. The validity of the TAC set for each species each year is heavily dependent on the accuracy and precision of the biomass estimates. The method used for both anchovy and sardine has been acoustic surveys on a random stratified grid covering the known range of the species. These surveys have, however, been designed according to the life history patterns of anchovy, which result in a particular occupation of the pelagic environment. This study investigated the shoaling dynamics of sardine at various scales in both the horizontal and vertical dimension in an attempt to ascertain whether these surveys are adequate to characterise the occupation of space by sardine. Hydro-acoustic data collected during 5 meso-scale surveys in 1994 and 1995 was used to study the shoaling dynamics of sardine, Sardinops sagax on the western Agulhas Bank of South Africa. Results of this study indicate the presence of spatial structure in sardine aggregations at both the shoal and meso-scale level.
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    Water quality requirements for first-feeding in marine fish larvae of the Cape of Good Hope, with description of developmental stages
    (1979) Brownell, Charles L; Brown, Alec C; Field, John G; Champion, Harold
    The tolerance of marine fish larvae to NH₃, NO₂⁻, NO₃⁻, H⁺, OH⁻, O₂, and CO₂ was investigated using the decrease in first-feeding incidence following a 24-h exposure as the criterion of response. Ten species, all hatched from pelagic eggs collected at sea, were used in the studies: two soleids (Heteromycteris, Synaptura), a cynoglossid (Trulla), a gadid (Gaidropsarus), a congiopodid (Congiopodus), four sparids (Diplodus, Lithognathus, Pachymetopon, and an unidentified species), and a centracanthid (Pterosmaris). Concentrations that inhibited first-feeding are compared to 24-h LC 50's for the same species, and to concentrations that are known to induce lethal and sublethal responses in other teleost species. Judging from their effect on first-feeding, un-ionized ammonia, elevated pH, and reduced oxygen concentration are considered to be potential hazards in the rearing tank. NO₂⁻, NO₃⁻, H⁺, and free CO₂ are nontoxic at levels likely to be encountered in practical fish culture. There are only minor inter-specific differences in calculated 24-h first-feeding EC 50's (concentration that reduces first-feeding incidence by 50%), which suggests general applicability of the results to a wide variety of first-feeding marine fish larvae. Data are presented on the age at first-feeding and point-of-no-return. The suitability of assorted micro-particles (including the rotifer, Proales, and Pine pollen) as experimental foods is discussed.