Browsing by Author "Cockcroft, Andrew"

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    Assessment of predation by the West Coast rock lobster (Jasus lalandii) : relationships among growth rate, diet and benthic community composition, with implications for the survival of juvenile abalone (Haliotis midae)
    (1998) Mayfield, Stephen; Branch, George M; Cockcroft, Andrew
    This thesis focused on two aspects of predation by the West Coast rock lobster (Jasus lalandii). These were (1) the problem of slow growth currently observed in adult male rock lobsters and the putative link between growth rate and food availability, and (2) the influence of rock-lobster predation on the benthos, but more specifically on sea urchins and juvenile abalone.
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    Biology and ecology of the deep-water rock lobsters Palinurus gilchristi and Palinurus delagoae in relation to their fisheries
    (2000) Groeneveld, Johan Conrad; Branch, George M; Cockcroft, Andrew
    Recent declines in the biomass of the closely-related deep-water rock lobsters Palinurus gilchristi and P.delagoae off South Africa suggest that both these resources are currently overfished, and that the existing management procedures are inadequate. A lack of detailed fisheries, biological and ecological knowledge is partly to blame, as this deficiency limits the scope and utility of resource assessments, and impairs the capacity of managers to forumulate species-specific management strategies. This thesis aimed to expand the biological and ecological bases on which effective resource assessment rests, and to recommend methods to improve the management of these deep-water rock lobster populations. The steps taken were: (1) determination and interspecies comparison of biological parameters, including spatial and temporal size composition trends, somatic growth rates, size at sexua maturity, female fecundity, mortality rates, moulting, recruitment and migration; (2) assessment of the effect of fishing with different gear types or arrays on abundance and its indices; and (3) incorporation of new information into resource assessments, with recommendations aiming to improve the management of the fisheries.