Browsing by Subject "hake"

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    A history of recent bases for management and the development of a species-combined Operational Management Procedure for the South African hake resource
    (National Inquiry Services Centre, 2010) Rademeyer, Rebecca A; Plagányi, Éva E; Butterworth, Doug S
    The bases for historical catch limits placed on the hake fishery are reviewed in brief for earlier years and then in some depth over the period from 1991 when the Operational Management Procedure (OMP) approach was introduced for this fishery. The new OMP implemented from 2007 was the first to be based on the use of rigorous species-disaggregated assessments of the resource as Operating Models. The paper describes the Reference Set and range of robustness trials, together with the associated Operating Models, which were used for the simulation testing of the new OMP. Performance statistics for a number of candidate OMPs are compared, and the two key trade-off decisions in the selection process discussed (substantial Merluccius paradoxus and catch per unit effort [CPUE] recovery, and total allowable catch [TAC] stability constraints). Details of the OMP adopted and how its formulae depend on recent trends in CPUE and survey estimates of abundance are provided. OMP-2007, which is tuned to a median 20-year recovery target of 20% of pristine spawning biomass for M. paradoxus and a 50% increase in CPUE over the next 10 years, has been adopted for recommending hake TACs over the 2007–2010 period until the next scheduled major review. A set of general guidelines adopted for the process of possible overruling of recommendations from OMPs or bringing forward their reviews within an otherwise intended four-year cycle is detailed.
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    Incorporating cannibalism and inter-species predation effects into the hake assessment model: Methods and some preliminary results
    (2013) Ross-Gillespie, Andrea; Butterworth, Doug S
    Hake cannibalism and inter-species predation is modelled explicitly using a Type II functional response. Because of the fast dynamics of predation compared to other processes, the standard hake assessment model is converted from a yearly to a monthly time-step. Convergence of model fits is difficult to achieve both because of providing good estimates for starting values and of the tendency of the model towards oscillating behaviour. Thus far satisfactory fits have been obtained only from a somewhat reduced level of predation compared to that thought to occur. These results suggest that both hake species are at higher levels relative to pristine than for the standard assessment.
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    An initial attempt at a spatially structured stock assessment for the South African hake resource including movement based on a gravity model.
    (2014) Rademeyer, Rebecca A
    The movement model for assessing the South African hake populations which was presented to last year’s review workshop is simplified by applying the “gravity” method to model movement. This reduces the numbering of movement parameters estimated from 234 to 68. This results in recent biomass estimates which are slightly more precise and somewhat lower in both absolute terms and relative to estimated pre-exploitation levels. Areas for possible future research are discussed briefly.
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    Overview of the South African west coast rock lobster, hake and pelagic resources and fisheries
    (2007) Johnston, Susan J; Cunningham, Carryn L; Rademeyer, Rebecca A; Butterworth, Doug S
    The commercial fishery for Jasus lalandii, the South African West Coast rock lobster, began in the late 1800s and at its peak in the early 1950s yielded an annual catch of 17 000t. Although this annual catch has dropped to only some 2000t over recent years, the fishery remains South Africa’s third most valuable in terms of landed value. Figure 1 illustrates the historic catch trend.