OpenUCT :: Browsing by Author "Glazer, Jean Patricia"

Browsing by Author "Glazer, Jean Patricia"

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Open Access
The 2006 operational management procedure for the South African Merluccius paradoxus and M. capensis resources
(2006) Rademeyer, Rebecca A; Glazer, Jean Patricia
The algorithm for the 2006 Operational Management Procedure (OMP) to provide TAC recommendations for the South African Merluccius paradoxus and M. capensis resources is empirical, increasing or decreasing the TAC in relation to the magnitude of recent trends in CPUE and survey abundance estimates for both species. The basis for the associated computations is set out below.
Open Access
The 2010 operational management procedure for the South African Merluccius paradoxus and M.?capensis resources
(2010) Rademeyer, Rebecca A; Fairweather, T; Glazer, Jean Patricia; Leslie, R L; Butterworth, Doug S
The algorithm for the 2010 Operational Management Procedure (OMP) to provide TAC recommendations for the South African Merluccius paradoxus and M. capensis resources is empirical. It combines an increase or decrease of the TAC in relation to a) the magnitude of recent trends in CPUE and survey abundance estimates for both species and b) the relative level of recent CPUE and survey abundance estimates compared to a target level. The basis for the associated computations is set out below, with the tuning parameters given in Table 1. Details of the computation procedures for the CPUE and catch data are provided in Appendix A, and for the survey estimates of Biomass in Appendix B.
Open Access
Alternative calculation of catches per Area in the South Coast rock lobster fishery
(2008) Glazer, Jean Patricia; Butterworth, Doug S
A method to separate the South Coast rock lobster annual catches by Area for the areadisaggregated assessments was described in WG/04/08/SCRL08. Concern was raised about an assumption made with respect to the calculation of those catches, namely that the spatial distribution for HBF was the same as for other companies over the period in which HBF under-reported catches (19971 -2000). The calculations presented in this paper offer an alternative method of separating the annual catches, taking the concern raised above into account.
Open Access
The application of a generalized linear mixed model to the Area 8 bakkie data
(2011) Glazer, Jean Patricia; Butterworth, Doug S
A Generalized Linear Mixed Model (GLMM) has been applied to the Area 8 bakkie CPUE data. The intention was to include data from Areas 10, 11 and East of Hangklip (Areas 12-14) in the analyses and to include subarea as a factor in the model, but preliminary results indicated that extending to these other Areas did not produce satisfactory results within a random-effects framework. This paper therefore reports standardized indices of abundance for the bakkie fishery from Area 8 only, including sub-area as an effect in the model. A procedure has been adopted to adjust the standardized index to allow for the movement of lobster into the East of Hangklip area over a period of time (1987-1995). The index is then extended back to 1986 by scaling the pre-1992 indices from the model applied in the past to standardize the Area 8 CPUE data, so that they can be incorporated with the GLMM-based index.
Open Access
The application of a generalized linear mixed model to the Area 8+ trapboat data
(2011) Glazer, Jean Patricia; Butterworth, Doug S
Two papers by Glazer and Butterworth (2011a, 2011b) were recently submitted to the West Coast Rock Lobster Scientific Working Group meeting for consideration. The first of those included sub-area as an explanatory variable in a Generalized Linear Mixed Model (GLMM) applied to standardize the Area 8 trapboat CPUE data. The second paper incorporated data from Area 8+ (rather than data from Area 8 only as used in the past) in the standard Generalized Linear Model (GLM) applied to those data. It was agreed at the meeting that the analyses presented in the aforementioned papers be amalgamated by conducting a GLMM on the Area 8+ data, which incorporates sub-area as an explanatory variable in the model. The results of such an analysis are presented in this paper. It should be noted that Area 8+ for trapboat fishing comprises data from Areas 8, 10 and 11. No trapboat fishing takes place in the area East of Hangklip (Areas 12-14) and a procedure has therefore been adopted to adjust the standardized index to allow for the movement of lobster into the East of Hangklip area over a period of time (1987-1995). The index obtained above is then extended back to 1985 by scaling the pre- 1992 indices from the model applied in the past to standardize the Area 8 CPUE data, so that they can be incorporated with the GLMM-based index.
Open Access
The application of general linear modelling methods to estimate trends in abundance of the hake and rock lobster stocks off South Africa
(1999) Glazer, Jean Patricia; Butterworth, Doug S
The two species of Cape hake, Merluccius capensis (shallow-water hake) and M paradoxus (deepwater hake), fomi the mainstay of the bottom trawl industry off South Africa and constitute the country's most valuable fishery. It is therefore important that the status of this resource be assessed regularly to ensure that exploitation is at a sustainable level. The two Cape hake species are morphologically similar and no distinction is made between them in commercial catch statistics. Consequently, for assessment purposes, the Cape hakes are treated as a single species. It is assumed that two stocks of Cape hake exist, one off the West Coast and another off the South Coast of South Africa. Central to the assessments of these stocks are the catch per unit effort (CPUE) data because it assumed that CPUE is proportional to abundance. The nominal CPUE (hake catch divided by actual time trawled) for both the West and South Coast stocks has shown a steady growth over the period 1978 - 1994, increasing at a rate of 3.8% per annum on the West Coast and 4.2% per annum on the South Coast. The bulk of this thesis is concerned with determining whether these increases in CPUE are the result of an increasing biomass, or are rather, in part, the result of improved vessel efficiency due to technological advancement or of changes in fishing strategy. The existing CPUE time series had previously been standardised by means of applying power factors which were crudely estimated in the early 1970s and which are likely inappropriate for the current fishing fleets. These CPUE series have therefore been re-standardised by applying the internationally accepted approach of General Linear Modelling (GLM).
Restricted
A Bayesian analysis of the squid resource Loligo reynaudii
(2012) Glazer, Jean Patricia; Butterworth, Doug S
A Bayesian assessment of the squid resource was last performed in 2010. This paper presents results from an updated Bayesian assessment given that additional years’ data are now available.
Restricted
A comparison of the catch and fishing day statistics from the squid LTRAMP and NMLS databases
(2006) Glazer, Jean Patricia; Butterworth, Doug S
Long-term rights were recently allocated to 109 companies with a total of 123 vessels in the squid jig fishery. An exercise was conducted to compare information provided in the LTRAMP application forms with that which is captured on the National Marine Linefish System (NMLS). This comparison applies only to the annual catches and days fished per company over the 2002-2004 period. Tables 1-4 present these comparisons and it is the last column, which indicates the percentage of the NMLS data that is reported in the LTRAMP database, that is most important
Restricted
Considerations for effort restrictions in 2007 in the South African jig fishery
(2006) Glazer, Jean Patricia; Butterworth, Doug S
It is proposed that effort in the jig fishery be curbed, and that the reduction in effort be effected by restricting each vessel to a vessel-dependent number of days at sea each year. The vessel-dependent numbers may be based upon the relative numbers of days-at-sea achieved by each vessel in 2005, for example, or alternatively on average over a few recent years.
Restricted
A conversion of squid effort from hours to man-days and some related considerations
(2006) Glazer, Jean Patricia; Butterworth, Doug S
The South African jig squid fishery is a constant effort fishery, with the current unit of effort being one of man-hours. The target effort level is 3030 thousand man-hours based on recent assessment results, and the mechanism of effort control is to limit the number vessels (and crew) active in the fishery. The long term rights allocation process resulted in 109 companies with a complement of 123 vessels (and 2233 crew) being granted rights in this fishery. 214 crew and 16 vessels have been set aside for appeals. It is of concern that the target effort level has been exceeded in recent years (Figure 1), which suggests that the current restrictions on effort are not adequate. Measures that might be invoked to reduce effort include, for example, capping the days spent at sea, lengthening the closed season, introducing an additional closed season or combinations of these.
Restricted
An experimental assessment of the impact of gear saturation on an abundance index for an exploited rock lobster resource
(Elsevier, 2003) Groeneveld, Johan Conrad; Butterworth, Doug S; Glazer, Jean Patricia; Branch, George M; Cockcroft, Andrew C
Increased fishing effort may downwardly bias indices of abundance, such as catch-per-unit-effort (CPUE), due to gear saturation. A field experiment was developed to assess gear-saturation effects on an index of relative abundance used for stock-assessments of rock lobster, Palinurus gilchristi, off South Africa. A progressive decrease in the value of the index, which is derived from commercial trap catch rates after accounting for the influences of vessel characteristics, trap soak-times, depth, area and month, has led to cuts in the total allowable catch (TAC) over the past 10 years. Concerns have been raised, however, that recent steep increases in fishing effort might have led to gear saturation effects, so that the index may now underestimate abundance relative to periods of lower effort, and hence the resource may not have declined to the extent that the index suggests. In the experiment, the fishing grounds were subdivided into the Agulhas Bank and Eastern fishing grounds, and both areas were subjected to three 2-month treatments of either unrestricted fishing effort or reduced fishing effort. In both areas, fishing in the first 2 months was unrestricted. In the second 2-month period, the number of trap-days was reduced by 25–30%, whereas in the third 2-month period this number was further reduced on the Agulhas Bank (by 65%), but increased by 25% on the Eastern fishing grounds. In terms of the saturation hypothesis, CPUE was predicted to rise during periods when effort was reduced. Changes in CPUE were assessed by expressing CPUE during periods of reduced effort as a proportion of CPUE during periods of unrestricted effort. These proportions were compared to proportions for equivalent time periods in previous years (1991–1998) when fishing effort was always unrestricted. The null hypothesis that CPUE is unaffected by effort (i.e. no gear-saturation effect) was rejected in only one of four treatments. In the other three treatments, the experiment failed to separate responses to effort-manipulations from those due to seasonal and areal fluctuations in catchability. However, a model that integrates the results of all four treatments suggests that, if GLM-standardized effort is used as the index of potential saturation, there is only a 2.5% probability that saturation could account for as much as 0.004 of the drop in CPUE from 0.15 to 0.09 kg tails/trap between 1991/1992 and 1997/1998. If trap-days instead are used as the saturation index, this 0.004 figure increases, but only to 0.03. This thus suggests with very high probability that saturation effects cannot alone explain the drop in CPUE in the fishery during the 1990s.
Open Access
Further analyses of the GLM trends for M. paradoxus and M. capensis
(2008) Glazer, Jean Patricia; Butterworth, Doug S; Leslie, R W
This paper takes a closer look at CPUE analyses, particularly with a view towards determining the reason for the sharp decline in the standardized CPUE index from 2006 to 2007 for M. capensis. Results from including and excluding night-time trawls are also presented from an analysis of data covering the period 2000-2007.
Open Access
Further squid assessment and projection results for a Bayesian approach to take account of uncertainty in parameter values
(2013) Glazer, Jean Patricia; Butterworth, Doug S
The squid stock assessment model has recently been updated to be based upon the Baranov catch equations rather than the Pope catch equations used in past analyses as advised by the Panel from the International Stock Assessment Meeting held in November 2012. A Bayesian analysis was attempted given the updated model and the results from this analysis are presented here. The priors used for this Bayesian assessment are shown in Table 1.
Restricted
Further squid statistics relevant to the data cleaning process
(2008) Glazer, Jean Patricia; Butterworth, Doug S
At the squid working group meeting held on 4 July 2008, the following further information was requested to inform the data cleaning process: • Distribution of fishing days for each of the 12 vessels identified by Industry in MCM/2008/July/SWG-SQ/01 for the period 1995-2006. • Distribution of catch for each of the 12 vessels identified by Industry in MCM/2008/July/SWG-SQ/01 for the period 1995-2006. • Annual distribution of squid-fishing days over the period 1995-2006.
Restricted
A Generalized Linear Model applied to the South Cost rock lobster CPUE data to obtain area-specific indices of abundance
(2008) Glazer, Jean Patricia; Butterworth, Doug S
Area-disaggregated assessments for South Coast rock lobster are currently being developed. An important input to these assessments is the catch per unit effort (CPUE) data. A Generalized Linear Model (GLM) has been applied to the data to obtain areaspecific standardized indices of abundance for input to the assessment models.
Open Access
The inclusion of sub-areas in the standardisation of the Area 8 trapboat CPUE data through the application of a generalised linear mixed model
(2011) Glazer, Jean Patricia; Butterworth, Doug S
Data for the West Coast rock lobster Areas are available at a sub-area level from 1992. The data are fairly patchy at a sub-area level for most areas other than Area 8 for trapboats and Area 1 for bakkies. This paper presents preliminary results from an analysis of the trapboat Area 8 CPUE data where the sub-areas are included as factors in the model.
Open Access
OMP 2007 re-cast to be used for setting TACs for the West Coast rock lobster fishery for the 2008+ seasons
(2010) Johnston, Susan J; Butterworth, Doug S; Glazer, Jean Patricia
This document first gives the reasons why the OMP agreed for West Coast rock lobster in 2007 (OMP-2007) was “re-cast” the following year, listing the modifications then introduced. It then provides details of the three main components of “OMP-2007 re-cast”: 1) how data are combined across the five super-areas (Area 1-2, Area 3-4, Area 5-6, Area 7 and Area 8) for input into the OMP; 2) the OMP formulae which provide the global TAC recommendation; and 3) the manner in which the global TAC is split amongst super-areas and resource usergroups
Open Access
OMP 2008 for South Coast rock lobster resource
(2008) Johnston, Susan J; Butterworth, Doug S; Glazer, Jean Patricia
OMP 2008 consists of an algorithm that calculates the TAC for the resource using CPUE data collected from each of three areas (New Areas 1, 2 and 3 – see Fig. 1), Note that the TAC for season y+1 will be based upon the CPUE series that ends in season y-1, i.e. the TAC recommendation for 20081 would be based on a CPUE series that ended with the most recent CPUE value available at the time a recommendation was requested which would be for 2006.
Open Access
OMP 2011 to be used for setting TACs for the west coast rock lobster fishery for the 2011+ seasons
(2012) Johnston, Susan J; Butterworth, Doug S; Glazer, Jean Patricia; Brandão, Anabela
This document provides full specifications of OMP 2011 to be used to set allocations for various sectors and super-areas for the 2011+ seasons for the West Coast rock lobster fishery. This OMP is implemented slightly differently for the first season (2011), than for 2012+. The management objective is to increase the male biomass above 75mm CL by 35% by 2021 relative to the 2006 level in median terms. This document provides details of the three main components of OMP 2011: 1) how data are combined across the five super-areas (Area 1-2, Area 3-4, Area 5-6, Area 7 and Area 8+) for input into the OMP; 2) the OMP formulae which provide the global TAC recommendation; and 3) the manner in which the global TAC is split amongst the super-areas and different sectors.
Open Access
A preliminary assessment of the South African east coast sole resource, Austroglossus pectoralis
(2014) Butterworth, Doug S; Glazer, Jean Patricia
Currently the Agulhas sole resource is managed by a Total Allowable Catch (TAC) which, for 2014, was set at 872 tons. Concern was expressed in the 2013 sole TAC recommendation regarding the fact that catches have, since 2002, been consistently below the TAC. In addition there has been a sharp decline in CPUE since 2009. As a result of the low catches and declining CPUE it was recommended that a task team be appointed to develop an effort limit programme for this particular fishery to be applied in conjunction with the existing TAC. This paper reports results from the application of a modified dynamic Schaefer production model fitted (coarsely) to the CPUE of sole specialists in six of the nine grid blocks which comprise the sole grounds in order to guide the effort limit-setting process.