Browsing by Subject "results"

Now showing 1 - 5 of 5
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    Analyses of the results from the island closure feasibility study for the Dassen/Robben and St Croix/Bird Island Pairs
    (2014) Robinson, William M L; Butterworth, Doug S; Furman, Liam B
    The results from the Island Closure Feasibility Study are analysed using the GLMs as set out at the 2010 international stock assessment workshop. Estimates of residual variance for a random year effects GLM for the various penguin response variables are considered to be sufficiently precise to enable power analyses to be conducted to contribute to the evaluation of whether to transition to a full experimental closures programme, so that the feasibility study may be considered successfully concluded. For the Dassen and Robben Islands about 80% of the estimates of the fishing effect parameter λ are positive, with this same proportion maintained for those (about one sixth) of these estimates which are significant at the 5% level. Thus the preponderance of the evidence from these analyses is that the impact of fishing around these islands has been positive. The rather fewer instances available to analyse for the Eastern Cape colonies suggest a weakly positive effect at Bird Island, but a somewhat stronger negative effect at St Croix. The power analyses suggest that in cases for Dassen and Robben Islands where further data collection might render currently non-significant λ estimates significant at the 5% level within the next two decades, the likely period required for such further collection would typically be in the vicinity of five years. The advantage provided by continuing the closure programme itself seems however to be slight, as the natural variation over time in normal catches would be sufficient to provide the contrast to achieve such results with only typically two years’ extension to those five years. For the two Eastern Cape islands, it seems that results which are statistically significant at the 5% level seem unlikely to be achieved in the foreseeable future – a result which may be a consequence of the relatively low levels of sardine catches typically taken close to those islands.
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    Detailed methodology and results for the final reference set of the South African Merluccius paradoxus and M. capensis resources for use in OMP testing
    (2006) Rademeyer, Rebecca A; Butterworth, Doug S
    This document gives detailed methodology, data and results for the final Reference Set for the joint assessment of the South African M. paradoxus and M. capensis resources that will be used in OMP testing.
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    Open Access
    Overall results for the effect of the presence of an observer on catches made by the pelagic fleet
    (2005) Somhlaba, S; Brandão, Anabela; Butterworth, Doug S
    The analysis of the observer data for the pelagic fishery is taken further for the complete data base from 1999 to 2004. Previously the analysis had been based on steel vessels (Somhlaba et al., 2005); those findings showed that there were statistically significant positive effects on catches given the presence of an observer on the steel vessels. The results below include the analysis of the combined data for all three categories of vessels: bait, ordinary and steel vessels. Sardine and anchovy data were analysed in detail using one model but with two different error structures: one lognormal (henceforth termed LogCPUE) and the other Poisson (henceforth termed catch).
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    Open Access
    Preliminary results of observer effect on pelagic fleet taking into account observer data from 1999 to 2011
    (University of Cape Town, 2014) Somhlaba, S; Brandão, Anabela; Butterworth, Doug S; van der Westhuizen, J
    A detailed update of the study of the data collected by scientific observers onboard the pelagic vessels is currently underway. The use of small pelagic commercial data base and an observer data base to investigate the effect of observers onboard commercial vessels has been an ongoing study since the mid-2000s (e.g. see Somhlaba et al, 2005, 2006, 2007). This paper updates those studies by including data from the more recent years 2008 to 2011.
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    WCRL area-disaggregated OMP output: task group results
    (2007) Johnston, Susan J; Butterworth, Doug S
    These results are for the “OMP2” presented in WG/04/07/WCRL1. Results have been updated using the “observed” 2005 somatic growth data provided by James Gaylard. (Note: 2005 refers to the 2005/06 season.) The previous program also had an “error” in that it added “noise” to all (1993+) trap and hoop CPUE input data into the OMP, instead of treating the 1993-2004 values as “observed” and only adding noise to the 2005+ generated data. The OMPs presented here are meant to be tuned so that the average commercial TAC over the 10-year period is either 2000 MT, 2200 MT or 2400 MT. Due to lack of time, the current tuning is approximate in these values being 2028 MT, 2244 MT and 2395 MT.