Browsing by Subject "poaching"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Restricted
    A spatial- and age-structured assessment model to estimate the impact of illegal fishing and ecosystem change on the South African abalone Haliotis midae resource
    (National Inquiry Services Centre, 2010) Plagányi, Éva E; Butterworth, Doug S; ;
    The management of abalone stocks worldwide is complicated by factors such as illegal fishing combined with the difficulties of assessing a sedentary (but not immobile) resource that is often patchily distributed. The South African abalone Haliotis midaefishery is faced with an additional problem in the form of a relatively recent movement of rock lobsters Jasus lalandii into much of the range of the abalone. The lobsters have heavily reduced sea urchin Parechinus angulosus populations, thereby indirectly negatively impacting juvenile abalone which rely on the urchins for shelter. A model is developed for abalone that is an extension of more standard age-structured assessment models because it explicitly takes spatial effects into account, incorporates the ecosystem change effect described above and estimates the magnitude of substantial illegal (‘poached’) catches. The model is simultaneously fitted to catch per unit effort and Fishery-Independent Abalone Survey abundance data, as well as to several years of catch-at-age (cohort-sliced from catch-at-size) data for the various components of the fishery and different spatial strata. It constitutes the first quantitative approach applied to the management of this commercially valuable resource in South Africa and has provided a basis for management advice over recent years by projecting abundance trends under alternative future catch levels.
  • Thumbnail Image
    Item
    Open Access
    Summary of estimates of recent trends in abalone poaching
    (2011) Maharaj, G; Butterworth, Doug S
    Preliminary analyses using three separate indices to estimate the trend in poaching suggest that the target of a 15% per annum reduction commencing October 2009 in poaching has not been reached. In fact, all indices suggest an increase in poaching. The 15% per annum decline was the key criterion for rebuilding the abalone resource and was amongst the conditions set by the Minister associated with reopening the fishery.