Browsing by Author "Glazer, Jean"

Now showing 1 - 11 of 11
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    The 2018 Operation Management Procedure for the South African Merluccius paradoxus and M. capensis Resources
    (2019) Ross-Gillespie, Andrea; Butterworth, Doug S; Glazer, Jean; Fairweather, Tracey
    Specifications and projection results for the 2018 Operational Management Procedure used for setting South African hake Total Allowable Catches are provided along with various background information, including details of the metarule processes.
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    The 2018 Operational Management Procedure for the South African Merluccius paradoxus and M. capensis resources.
    (2018-10) Ross-Gillespie, Andrea; Butterworth, Doug S; Glazer, Jean; Fairweather, Tracey
    Specifications and projection results for the 2018 OMP used for setting SA hake TACs are provided along with various background information, including details of the metarule process.
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    2020 sole dynamic Schaefer production model results
    (2020) Glazer, Jean; Butterworth, Doug
    The sole resource is modelled by a dynamic Schaefer production model which allows for a drop in the value of the intrinsic growth rate parameter from 2000 onwards. The model is fit to the available CPUE and survey abundance indices. These data are not sufficiently informative to be able to distinguish amongst fairly wide ranges of pre- and post-2000 intrinsic growth rate parameters. Nevertheless, all suggest that the sole resource has never been substantially depleted (being well above its MSY level), and furthermore that the current replacement yield and MSY are reasonably robustly estimated in the ranges of 275-350 and 490-720 mt respectively. Given that this update 2020 assessment indicates slightly lower values for resource productivity than in 2019, consideration should be given to some reduction in the current TAC of 502 mt.
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    Adjustments made to recent catches and CPUE for West Coast Rock Lobster in Areas 3+4 and 5+6
    (2018-08) Butterworth, Doug S; Glazer, Jean; Johnston, Susan; van Zyl, Daniel
    During the 2017/18 fishing season, some catches made in Area 3+4 by trapboats were landed in Area 5+6 as hoopnet catches. This document reports the methodology used and the results obtained from an attempt to correct the catches reported for these super-areas to adjust for this malpractice.
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    Considerations on management of the chokka squid jig fishery with reference to the pending FRAP 2020 allocation of fishing rights and implementation of Small Scale Fisheries
    (2018-08) Mwicigi, Jean; Durholtz, Deon; Glazer, Jean; Butterworth, Doug S
    The South African squid jig fishery is primarily managed using effort control. The management objective for the fishery is to cap effort at a level that secures the greatest catch, on average, in the longer term without exposing the resource to the threat of reductions to levels which future recruitment success might be impaired or catch rates drop below economically viable levels. Assessments of the dynamics and status of the resource, and subsequent scientific advice on the management of the jig fishery targeting the resource (primarily expressed as a Total Allowable Effort recommendation), are based on an effort metric of person-days. The current TAE is set at 270 000 person-days. Fishing Rights are, however, allocated in terms of the number of fishers that are permitted to operate in the fishery (2 451 fishers). This mismatch has required that within the current structure of the fishery an additional closed season has had to be implemented to ensure that the management objective for the fishery is not compromised. The implications in terms of the pending 2020 allocation of fishing rights and establishment of a Small Scale Fishery are discussed, and alternative management scenarios are explored.
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    Exploratory analyses of the Agulhas sole assessment
    (2018-03) Glazer, Jean; Butterworth, Doug S
    A number of different production model approaches are considered for assessment of the Agulhas sole resource, Stationary models, either with observation error only estimation, or adding annual process error, exhibit systematic patterns in residuals. The best approach seems to be to postulate a non-stationary situation, with some change in the dynamics of the resource (or equivalently in the fishery catchability q) in the new century. Some initial comments are made as regards the next steps needed to advance this approach further.
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    Further sole dynamic Schaefer production model results
    (2019) Butterworth, Doug S; Glazer, Jean
    The sole resource is modelled by a dynamic Schaefer production model which allows for a drop in the value of the intrinsic growth rate parameter from 2000 onwards. The model is fit to the available CPUE and survey abundance indices. These data are not sufficiently informative to be able to distinguish amongst fairly wide ranges of pre- and post-2000 intrinsic growth rate parameters. Nevertheless, all suggest that the sole resource has never been substantially depleted (being well above its MSY level), and furthermore that the current replacement yield and MSY are reasonably robustly estimated in the ranges of 300-400 and 500-650 mt respectively.
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    Hake Data: problems, solutions and GLM CPUE sensitivity to alternate scenarios
    (2009) Fairweather, Tracey; Glazer, Jean; Leslie, Rob; de Decker, Michelle; Johnston, Susan; Butterworth, Doug S
    The checks carried out on the hake offshore trawl catch and effort data, which provide the basis to split the catches by species and to obtain GLM-standardised CPUE indices of abundance by species, have focused on two separate steps. The first was a re-extract of the data from the original files to check for possible errors in the earlier extracts (this applies to the subset of the data for which size composition information can be unambiguously extracted). The second step was to increase the proportion of the data utilised (and at the same time to check for possible selection biases in the existing sample) by assigning size composition to drags for which this information was not directly available, on the basis of the average for other vessels for which this was available for the area and time at which the fishing concerned took place. The first step revealed a problem with extractions over the last few years which at times for certain vessels had linked the accumulated catch for the day with only the effort for the last trawl of the day, rather than for all trawls that day combined.
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    South coast rock lobster OMP 2019
    (2019) Johnston, Susan; Butterworth, Doug S; Glazer, Jean
    This document provides the full specification and rationale for the south coast rock lobster OMP 2019
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    An updated assessment of the Agulhas sole resource, Austroglossus pectoralis.
    (2018-10) Glazer, Jean; Butterworth, Doug S
    Butterworth and Glazer (2014) reported results from the application of a simple form of the dynamic Schaefer model to account for a large drop in sole CPUE over the period 2009-2013. The two hypotheses considered were (i) the drop in CPUE was a consequence of decreasing catchability and (ii) the drop in CPUE was a consequence of decreasing productivity. The model was applied again in 2016 (Butterworth et al., 2016) and 2017 (Glazer et al., 2017). Results from the assessment conducted in 2017 yielded more positive future projections for the most pessimistic scenario (a decrease in productivity, where effort remains at its current reduced level into the future). Recent biomasses were estimated to be higher and projected to decrease more slowly if the 2013 effort level was maintained. Given that data are now available for 2017, the assessment model has once again been updated, with results reported here. These point to yet a more positive resource situation.
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    Updated calculations related to the additional closed season.
    (2019) Glazer, Jean; Butterworth, Doug S; Durholtz, Deon
    The length of the additional closed season which would need to be applied to the squid jig commercial sector to keep effort within the TAE has been re-calculated taking into account that the TAE recommendation for the 2019/20 fishing season by the Squid Scientific Working Group is 295 000 person-days, and further information about effort levels applied in the fishery over recent years. These calculations suggest that the additional closed season should remain of three months duration.